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getting to grips with<BR>fuel economy<BR>Issue 3 - July 2004<BR>Flight Operations Support &amp; Line Assistance<BR>getting to grips with<BR>fuel economy<BR>Issue 3 - July 2004<BR>Flight Operations Support &amp; Line Assistance<BR>Customer Services<BR>1, rond-point Maurice Bellonte, BP 33<BR>31707 BLAGNAC Cedex FRANCE<BR>Telephone (+33) 5 61 93 33 33<BR>Telefax (+33) 5 61 93 29 68<BR>Telex AIRBU 530526F<BR>SITA TLSBI7X<BR>Getting to grips with Fuel Economy Table of contents<BR>- 1 -<BR>TABLE OF CONTENTS<BR>TABLE OF CONTENTS 1<BR>1. SUMMARY 4<BR>2. PREAMBLE 5<BR>3. INTRODUCTION 6<BR>4. PRE-FLIGHT PROCEDURES 7<BR>4.1 CENTER OF GRAVITY POSITION 8<BR>4.1.1 INTRODUCTION 8<BR>4.1.2 AUTOMATIC CENTER OF GRAVITY MANAGEMENT 8<BR>4.1.3 INFLUENCE ON FUEL CONSUMPTION 9<BR>4.2 TAKEOFF WEIGHT 11<BR>4.2.1 INTRODUCTION 11<BR>4.2.2 OVERLOAD EFFECT 11<BR>4.2.3 AIRCRAFT OPERATING WEIGHT 12<BR>4.2.4 PAYLOAD 13<BR>4.2.5 EMBARKED FUEL 13<BR>4.3 FLIGHT PLANNING 14<BR>4.4 TAXIING 17<BR>4.5 FUEL FOR TRANSPORTATION 19<BR>4.6 AUXILIARY POWER UNIT 21<BR>4.7 AERODYNAMIC DETERIORATION 23<BR>5. IN FLIGHT PROCEDURES 24<BR>5.1 Take-off and Initial Climb 25<BR>5.1.1 INTRODUCTION 25<BR>5.1.2 BLEEDS 25<BR>5.1.3 CONFIGURATION 25<BR>5.1.4 SPEEDS 26<BR>5.1.5 FLEX THRUST 26<BR>5.1.6 NOISE FLIGHT PATHS 26<BR>5.1.7 COURSE REVERSAL 26<BR>1 - Summary Getting to Grips with Fuel economy<BR>- 2 -<BR>5.2 CLIMB 27<BR>5.2.1 INTRODUCTION 27<BR>5.2.2 THE EFFECT OF CLIMB TECHNIQUE ON FUEL BURN 28<BR>5.2.3 CORRELATION OF FUEL BURN &amp; TIME WITH CLIMB TECHNIQUE 31<BR>5.2.4 CLIMB TECHNIQUE COMPARISON TABLES 34<BR>5.2.5 DERATED CLIMB 35<BR>5.3 CRUISE 36<BR>5.3.1 INTRODUCTION 36<BR>5.3.2 CRUISE ALTITUDE OPTIMISATION 37<BR>5.3.3 CRUISE SPEED OPTIMISATION 47<BR>5.3.4 WIND INFLUENCE 49<BR>5.3.5 MANAGED MODE 52<BR>5.3.6 EFFECT OF SPEED INCREASE ON MANAGED MODE 56<BR>5.4 DESCENT 57<BR>5.4.1 INTRODUCTION 57<BR>5.4.2 THE EFFECT OF DESCENT TECHNIQUES ON FUEL BURN 58<BR>5.4.3 MANAGED MODE DESCENT 60<BR>5.4.4 EARLY DESCENT 60<BR>5.5 HOLDING 62<BR>5.5.1 INTRODUCTION 62<BR>5.5.2 VARIOUS CONFIGURATION / SPEED COMBINATIONS 63<BR>5.5.3 LINEAR HOLDING 68<BR>5.6 APPROACH 70<BR>5.6.1 FLIGHT PATH PRIOR TO GLIDE SLOPE INTERCEPTION 70<BR>5.6.2 LANDING GEAR EXTENSION 70<BR>6. DETAILED SUMMARY 71<BR>6.1 INTRODUCTION 71<BR>6.2 General guidelines 71<BR>6.2.1 PRE-FLIGHT PROCEDURES 71<BR>6.2.2 TAKE-FF AND INITIAL CLIMB 72<BR>6.2.3 CLIMB 72<BR>6.2.4 CRUISE 72<BR>6.2.5 DESCENT 72<BR>6.2.6 HOLDING 73<BR>6.2.7 APPROACH 73<BR>6.3 FUEL SAVINGS 73<BR>6.4 ECONOMIC BENEFITS 75<BR>7. CONCLUSIONS 76<BR>Getting to grips with Fuel Economy Table of contents<BR>- 3 -<BR>8. APPENDICES 77<BR>APPENDIX A (Climb Charts) 78<BR>APPENDIX B (Descent Charts) 80<BR>1 - Summary Getting to Grips with Fuel economy<BR>- 4 -<BR>1. SUMMARY<BR>Fuel Consumption is a major cost to any airline, and airlines need to focus<BR>their attention on this in order to maintain their profitability. This brochure looks<BR>at all the significant operating variables that affect fuel economy for the current<BR>Airbus range of aircraft.<BR>This brochure shows that there are many factors that affect fuel consumption<BR>and that the potential gains and losses are huge. Most of these factors are directly<BR>controlled by the airlines own employees (flight crew, operations/dispatch,<BR>maintenance, etc.).<BR>It can be also seen that what is good for one type of aircraft is not<BR>necessarily good for another, and that certain conceptions regarding best<BR>techniques for fuel economy are wrong.<BR>Finally for a fuel and cost economic airline, the following are the main<BR>features:<BR>• Good flight planning based on good data.<BR>• Correct aircraft loading (fuel weight and CG).<BR>• An aerodynamically clean aircraft.<BR>• Optimal use of systems (APU, Bleed, Flaps/Slats, Gear, etc).<BR>• Flight Procedures using speeds and altitudes appropriate to the<BR>companies economic priorities.<BR>• Use of the FMGS in the managed mode.<BR>• Use of performance factors in flight planning and in the FMGS derived<BR>from an ongoing aircraft performance monitoring program.<BR>Getting to grips with Fuel Economy 2 - Preamble<BR>- 5 -<BR>2. PREAMBLE<BR>The very competitive and deregulated aviation market as well as the fear of<BR>a fuel price rise have made airlines understand how important it is to work on the<BR>fuel consumption of their fleet. Indeed airlines try to reduce their operational<BR>costs in every facet of their business, and fuel conservation has become one of<BR>the major preoccupations for all airlines, as well as aircraft manufacturers. That’s<BR>why all ways and means to reduce fuel costs have to be envisaged, safety being<BR>of course the number one priority in any airline operation.<BR>The purpose of this document is to examine the influence of flight operations<BR>on fuel conservation with a view towards providing recommendations to enhance<BR>fuel economy.<BR>It is very rare that the reduction of fuel used is the sole priority of an airline.<BR>Such instances are to maximize range for a given payload, or to decrease fuel<BR>uplift from a high fuel cost airport. Generally fuel is considered one of the direct<BR>operating costs and an airline tries to minimize total direct operating costs. This<BR>introduces the concept of Cost Index and is the scope of another brochure<BR>(Getting to Grips with the Cost Index). However it is sometimes necessary to<BR>consider the cost implication of a fuel economy, and this is done where necessary<BR>in this brochure.<BR>This brochure systematically reviews fuel conservation aspects relative to<BR>ground and flight performance. Whilst the former considers center of gravity<BR>position, excess weight, flight planning, auxiliary power unit (A.P.U.) operations<BR>and taxiing, the latter details climb, step climb, cruise, descent, holding and<BR>approach.<BR>None of the information contained herein is intended to replace procedures<BR>or recommendations contained in the Flight Crew Operating Manuals (FCOM), but<BR>rather to highlight the areas where maintenance, operations and flight crews can<BR>contribute significantly to fuel savings.<BR>3 - INTRODUCTION Getting to grips with Fuel Economy<BR>- 6 -<BR>3. INTRODUCTION<BR>This brochure considers the two flight management modes: “managed”<BR>mode and “selected” mode.<BR>The managed mode corresponds to flight management by means of a<BR>dedicated tool, the flight management system (FMS). Crews interface through the<BR>multipurpose control and display unit (MCDU) introducing basic flight variables<BR>such as weight, temperature, altitude, winds, and the cost index. From these<BR>data, the FMS computes the various flight control parameters such as the climb<BR>law, step climbs, economic Mach number, optimum altitude, descent law. Hence,<BR>when activated, this mode enables almost automatic flight management.<BR>When in managed mode, aircraft performance data is extracted from the<BR>FMS database. This database is simplified to alleviate computation density and<BR>calculation operations in the FMS, but individual aircraft performance factors can<BR>produce good correlation with actual aircraft fuel burns.<BR>When in selected mode, crews conduct the flight and flight parameters<BR>such as speed, altitude, and heading have to be manually introduced on the flight<BR>control unit (FCU).<BR>The cost index (CI) used in the managed mode provides a flexible tool to<BR>control fuel burn and trip time to get the best overall economics. A technique that<BR>reduces fuel burn often requires more trip time. Hence fuel savings are offset by<BR>time related costs (hourly maintenance costs, flight and cabin crew costs and<BR>marginal depreciation or leasing costs). The cost index is the cost of time ($/min)<BR>compared with the cost of fuel ($/kg) and is used to obtain the best economics.<BR>If fuel costs were the overriding priority, because fuel costs were much<BR>more significant than the cost of time, then the cost index would be low. With<BR>zero cost of time it would be zero and the FMS would fly the aircraft at Mach for<BR>max range (MMR).<BR>However if the cost of fuel was very cheap compared to the cost of time,<BR>then speed would be important and the CI would be high. For zero cost of fuel,<BR>the Cost Index would be 999 and the FMS would fly the aircraft just below MMO.<BR>Best economics would be between these two speeds and would depend on<BR>the operator’s cost structure and operating priorities. For more information on<BR>Cost Index see “Getting to Grips with the Cost Index”<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 7 -<BR>4. PRE-FLIGHT PROCEDURES<BR>Operation of the aircraft starts with the aircraft on the ground by aircraft<BR>maintenance, preparation and loading.<BR>This part intends to highlight the impact of some ground operations on fuel<BR>consumption. Even if these operations enable only little savings in comparison<BR>with savings made during the cruise phase, ground staff has to be sensitive to<BR>them and should get into good habits.<BR>This part is divided into seven different sections:<BR>• Center of gravity position<BR>• Excess Takeoff weight<BR>• Flight Planning<BR>• Ways of taxiing to save fuel<BR>• Auxiliary Power Unit<BR>• Fuel Tankering<BR>• Aerodynamic Deterioration<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 8 -<BR>4.1 CENTER OF GRAVITY POSITION<BR>4.1.1 INTRODUCTION<BR>The gross weight is the sum of the dry operating weight, payload and fuel<BR>and acts as one force through the center of gravity (CG) of the aircraft. The<BR>balance chart allows the determination of the overall center of gravity of the<BR>airplane taking into account the center of gravity of the empty aircraft, the fuel<BR>distribution and the payload. It must be ensured that the center of gravity is<BR>within the allowable range referred to as the center of gravity envelope.<BR>A more forward center of gravity requires a nose up pitching moment<BR>obtained through reduced tail plane lift, which is compensated for by more wing<BR>lift. This creates more induced drag and leads to an increase in fuel consumption.<BR>It is better to have the center of gravity as far aft as possible. As a rearward shift<BR>in CG position deteriorates the dynamic stability of the aircraft, the CG envelope<BR>defines an aft limit.<BR>4.1.2 AUTOMATIC CENTER OF GRAVITY MANAGEMENT<BR>AIRBUS has created a trim tank transfer system that controls the center of<BR>gravity of the airplane. This system is installed on some A300 and A310 aircraft<BR>and all A330 and A340 aircraft. When an airplane with a trim tank is in cruise, the<BR>system optimizes the center of gravity position to save fuel by reducing the drag<BR>on the airplane. The system transfers fuel to the trim tank (aft transfer) or from<BR>the trim tank (forward transfer). This movement of fuel changes the center of<BR>gravity position. The crew can also manually select forward fuel transfer.<BR>The Fuel Control and Management Computer (FCMC) calculates the center of<BR>gravity of the airplane from various parameters including input values (Zero Fuel<BR>Weight or Gross Take-off Weight and the associated CG) and the fuel tank<BR>contents. It continuously calculates the CG in flight. From this calculation, the<BR>FCMC decides the quantity of fuel to be moved aft or forward in flight to maintain<BR>the CG between the target value and 0.5% forward of the target band.<BR>Usually one initial aft fuel-transfer is carried out late in the climb to bring the<BR>CG within this band. During the flight there are several smaller forward<BR>movements as the fuel burn moves the CG more aft. Finally a forward transfer is<BR>made as the aircraft nears its destination to bring the CG within the landing CG<BR>range.<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 9 -<BR>4.1.3 INFLUENCE ON FUEL CONSUMPTION<BR>The following graph shows the change in fuel consumption, expressed in<BR>terms of specific range (nm per kg of fuel), for both a Forward (20%) and an Aft<BR>(35%) CG position compared to a mid CG position of 27% at cruise Mach.<BR>This graph, which is for the A310-203, shows the advantage of flying at aft<BR>CG. Also shown are the optimum altitude lines and these show the effects of CG<BR>to be constant at these altitudes, with almost no variation with aircraft weight.<BR>Other aircraft have similar shape curves with similar optimum altitude<BR>characteristics (except the A320 family). The following table summarizes the<BR>effect of CG on specific range at the optimum altitude :<BR>Aircraft Type Aft CG(35-37%) Fwd CG(20%)<BR>A300-600 +1.7% -0.9%<BR>A310 +1.8% -1.8%<BR>A330 +0.5% -1.3%<BR>A340 +0.6% -0.9%<BR>For the A300/A310 reference CG is 27% and aft CG is 35%.<BR>For the A330/A340 reference CG is 28% and aft CG is 37%.<BR>Specific Range variation with CG position<BR>-3%<BR>-2%<BR>-1%<BR>0%<BR>1%<BR>2%<BR>3%<BR>290 310 330 350 370 390 410 430<BR>Flight Level<BR>SR Variation<BR>140t<BR>140t<BR>130t<BR>130t<BR>110t<BR>110t<BR>90t<BR>90t<BR>Weight 35%<BR>27%<BR>20%<BR>CG<BR>OPT FL<BR>OPT FL<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 10 -<BR>At maximum altitude, the change in fuel consumption given in the table is<BR>larger by up to 1%. However no benefit is obtained, as the specific range (SR) is<BR>lower at aft CG at maximum altitude than at mid CG at optimum altitude.<BR>For aircraft that are not fitted with automatic center of gravity management,<BR>not all these advantages may be realized because of the normal forward and<BR>rearward shift of CG in flight due to fuel burn. In addition loading these aircraft at<BR>max fuel to an aft CG could prove difficult.<BR>The A320 family does not show the same SR variation with CG as the other<BR>aircraft. The aft CG produces worst SR at FL290, crossing over to show an<BR>improvement at higher flight levels. The SAR variation is much smaller also. This<BR>is due to a complex interaction of several aerodynamic effects. The SAR can be<BR>considered effectively constant with CG position. Loading is therefore not critical<BR>for fuel economy for the A320 family.<BR>In order to assess the overall impact of CG variation on fuel burn, it must be<BR>assessed on a complete sector. The following table shows increases in fuel<BR>consumed with a more forward CG. It is expressed as kg per 1000nm sector per<BR>10% more forward CG for the max variation case (high weight, high flight level)<BR>with no in flight CG shift. The fuel increment in kg is also given for the Forward<BR>(20%) position, compared with the Aft (35 or 37%) position, for a typical sector.<BR>Fuel Burn Increase with a more Forward CG<BR>Aircraft types Fuel increment<BR>KG/1000nm/10%CG<BR>Typical Sector distance<BR>(nm)<BR>Fuel increment per<BR>sector (kg)<BR>A300-600 240 2000nm 710<BR>A310 110 2000nm 330<BR>A319/A320/A321 Negligible 1000nm Negligible<BR>A330-200 70 4000nm 480<BR>A330-300 90 4000nm 600<BR>A340-200 90 6000nm 900<BR>A340-300 80 6000nm 800<BR>A340-500 150 6000nm 1550<BR>A340-600 130 6000nm 1300<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 11 -<BR>4.2 TAKEOFF WEIGHT<BR>4.2.1 INTRODUCTION<BR>Another way to save fuel is to avoid excess take-off weight, which consists of<BR>the operating empty weight of the aircraft plus the payload plus the fuel.<BR>In addition accurate knowledge of weight is an important factor needed to<BR>ensure that fuel burn predictions are met. This gives pilots confidence in the flight<BR>plans thus reducing the tendency to carry excess fuel.<BR>4.2.2 OVERLOAD EFFECT<BR>The specific range, flying at given altitude, temperature and speed depends<BR>on weight. The heavier the aircraft, the higher the fuel consumption.<BR>In addition, fuel savings can be made during climb since the aircraft would<BR>reach its optimal flight level earlier if it were lighter.<BR>The effect of overloading with respect to the in-flight weight is shown on the<BR>following graph, for an excess load of 1% of MTOW (2600kg) in cruise for an<BR>A340-313 This shows the increase in specific range penalty with both weight and<BR>altitude. Maximum and optimum altitudes are shown together with selected sub<BR>optimum flight levels representing the choice of a FL below the Optimum instead<BR>of above it. For example, at 220t the optimum altitude is just under FL 350. If we<BR>select FL 330 1% extra MTOW will decrease the specific range by just under 1.2%<BR>Specific Range Penalty for Excess Weight of 1% MTOW<BR>A340-313 ISA MN 0.82<BR>0.00%<BR>0.50%<BR>1.00%<BR>1.50%<BR>2.00%<BR>2.50%<BR>120 140 160 180 200 220 240 260 280 300<BR>Aircraft Weight - Tonnes<BR>Decrease in SR<BR>Optimum<BR>Altitude<BR>Maximum<BR>Altitude<BR>Selected Sub<BR>Optimum FL<BR>FL410 FL390<BR>FL370<BR>FL350 FL330<BR>FL310<BR>FL290<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 12 -<BR>The characteristic curves for the other aircraft types have a similar shape.<BR>Calculating the weight effect on specific range on all Airbus aircraft in accordance<BR>with the lower boundary of typical flight levels gives an average reduction of 1%<BR>of SR for a weight increase of 1% of Maximum Take-off Weight. The scatter in this<BR>value is generally within .2%.<BR>At the higher altitudes, obtainable at lower weights, the previous picture shows<BR>that the SR reduction can increase to 1.5%<BR>Overloading affects not only the trip fuel but also the reserves and requires<BR>increased fuel uplift for a specific mission. The following table shows the effect of<BR>1 tonne/1000nm and also 1% of basic MTOW for a typical sector, both at optimum<BR>altitude, assuming maximum passengers and some freight.<BR>Although the A320 family show considerably lower fuel burn penalties than<BR>the other aircraft, the total fuel penalty is of a similar order due to the high<BR>number of sectors per day. It can readily be seen that a 1% weight penalty has a<BR>significant impact on fuel costs when looked at on a yearly basis for a fleet of<BR>aircraft.<BR>4.2.3 AIRCRAFT OPERATING WEIGHT<BR>The operating empty weight of an aircraft is defined as the manufacturer’s<BR>weight empty plus the operator’s items. The latter include the flight and cabin<BR>crew and their baggage, unusable fuel, engine oil, emergency equipment, toilet<BR>chemicals and fluids, galley structure, catering equipment, seats, documents, etc.<BR>The OEW of new aircraft, even in the same fleet, can vary significantly, due<BR>to specification changes, build differences and normal scatter. Also aircraft<BR>Aircraft<BR>types<BR>Payload Weight<BR>Increase<BR>Stage Fuel Penalty<BR>1000nm/t<BR>Fuel penalty<BR>per sector<BR>Extra<BR>Reserves<BR>A300-600 31000 kg 1705 kg 2000 Nm 93 kg 320 kg 100 kg<BR>A310-300 26560 kg 1500 kg 2000 Nm 59 kg 240 kg 90 kg<BR>A318 14650 kg 640 kg 1000 Nm 31 kg 30 kg 30 kg<BR>A319 13000 kg 590 kg 1000 Nm 38 kg 50 kg 40 kg<BR>A320 17200 kg 735 kg 1000 Nm 43 kg 60 kg 45 kg<BR>A321 19100 kg 890 kg 1000 Nm 48 kg 55 kg 50 kg<BR>A330-200 29800 kg 2300 kg 4000 Nm 49 kg 460 kg 100 kg<BR>A330-300 29800 kg 2300 kg 4000 Nm 47 kg 440 kg 100 kg<BR>A340-200 29000 kg 2535 kg 6000 Nm 74 kg 1130 kg 170 kg<BR>A340-300 29000 kg 2535 kg 6000 Nm 87 kg 1330 kg 230 kg<BR>A340-500 35700 kg 3680 kg 6000 Nm 64 kg 1410 kg 210 kg<BR>A340-600 42250 kg 3650 kg 6000 Nm 65 kg 1420 kg 210 kg<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 13 -<BR>generally get heavier all through their operational life. This is due to repair<BR>schemes, service bulletins, equipment upgrades, dirt, rubbish and moisture<BR>accumulation and unnecessary equipment and supplies.<BR>This variation in weight requires regular monitoring for flight planning<BR>purposes. In general most weight growth is inevitable and it cannot be controlled<BR>at the operational level. However the airline has to be sensitive to these problems<BR>and efforts have to be made in order to avoid excess weight, such as dirt, rubbish<BR>and unnecessary equipment and supplies. It should be noted that 100kg of excess<BR>weight requires an additional 5000kg of fuel per year per aircraft.<BR>4.2.4 PAYLOAD<BR>The most important part of the take-off weight from an airlines point of view<BR>is the payload (passengers and freight). Generally the weight of passengers,<BR>carry-on baggage and checked bags are defined in the operating rules by the<BR>authorities such as the JAA or the FAA. Most operators use standard weights<BR>although other values may be used if they can be statistically demonstrated<BR>through surveys. In general there is not much an operator can do to change the<BR>situation. However they should be aware of the rules and their validity. If the<BR>weights do not seem appropriate then an operator should consider conducting a<BR>survey.<BR>As each freight consignment is weighed, the only influence it can have on<BR>fuel economy is its location and hence the aircraft CG.<BR>4.2.5 EMBARKED FUEL<BR>Fuel is loaded onto the aircraft to be used as follows:<BR>1. Start-up Fuel<BR>2. Taxi Fuel<BR>3. Trip Fuel<BR>4. Reserve Fuel<BR>5. Fuel for Transportation<BR>6. APU Fuel<BR>In order to avoid unnecessary fuel weight, the flight must be planned very<BR>precisely to calculate the exact fuel quantity to be embarked. Flight planning<BR>should be based on aircraft performance monitoring by taking into account<BR>performance factors derived from specific range variations. In addition the<BR>planning should be based on the appropriate optimized techniques using the best<BR>achievable routing and flight levels.<BR>More detailed information on this subject is given later in this brochure.<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 14 -<BR>4.3 FLIGHT PLANNING<BR>The fundamental requirement for achieving fuel economy and reduction of<BR>operating costs is a quality Flight Planning System.<BR>A good flight planning system will produce an optimized route, in terms of<BR>track, speeds and altitudes, which meets the operator’s economic criteria. This<BR>track and vertical profile must be normally achievable in operation, given the<BR>constraints of ATC, climb rates, descent rates, etc.<BR>Climb, cruise and descent techniques and cruise flight levels should be<BR>optimized in accordance with the operator’s criteria, for both the sector and the<BR>diversion. This is covered in much more detail in this brochure.<BR>It will be based on good quality data (temperature, wind, aircraft weight,<BR>payload, fuel uplift, etc)<BR>It will be use the correct aircraft performance and will include an<BR>individual aircraft performance factors derived from an ongoing aircraft<BR>performance monitoring (APM) program (see “Getting to Grips with Aircraft<BR>Performance Monitoring”).<BR>Having established the climb, cruise and descent techniques, it should be<BR>verified from time to time that the aircrews are using these techniques<BR>The fuel reserves will be based on a policy that aims at obtaining the<BR>minimum values required within the regulations.<BR>Within JAR OPS, there are several definitions of Contingency fuel,<BR>depending on diversion airfields, fuel consumption monitoring, etc. Full details can<BR>be found in “Getting to Grips with Aircraft Performance”, but briefly the fuel is the<BR>greater of two quantities:<BR>1. 5 minutes hold fuel at 1500 feet above destination at ISA<BR>2. One of the following quantities:<BR>5% of trip fuel,<BR>3% of trip fuel with an available en route alternate airport<BR>15 minutes hold fuel at 1500 feet above the destination at ISA<BR>20 minutes trip fuel, based upon trip fuel consumption.<BR>The last 3 options require airworthiness approval and the last 2 options<BR>require fuel consumption monitoring with fuel based on results. What we can<BR>conclude is that depending on the flight distance, there is a lowest contingency<BR>fuel.<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 15 -<BR>The following graphs show the different contingency fuel quantities for<BR>different distances for an A320.<BR>The graphs for other members of the A320 family are similar and indicate that<BR>below about 500nm, the contingency fuel is set by the minimum 5-minute hold<BR>value. Above about 1000nm, contingency fuel can be reduced to 3% of trip fuel if<BR>there is an en-route alternate available. If not, reductions can be made above<BR>about 2000nm by using the 15-minute destination hold option, which always<BR>requires less fuel than the 20 minute trip fuel option.<BR>The graphs for the other aircraft show different characteristics because of their<BR>longer-range capability.<BR>The A340-600 picture, on the following page, indicates that with no enroute<BR>alternate the 15-minute destination hold requirement enables the<BR>contingency fuel to be reduced above 2150nm. An en-route alternate will give<BR>more benefit until 3500nm, beyond which the 15-minute destination hold<BR>minimises the contingency fuel requirement. The A340-500 is similar.<BR>The A300, A310, A330 and other A340’s have slightly different critical<BR>distances as follows:<BR>5% trip fuel/15-minute hold 1700 to 1900nm.<BR>3% trip fuel/15-minute hold 2800 to 3200nm<BR>However these will also vary with weight, winds, temperature, etc so<BR>the limiting reserve should always be checked. Each aircraft type will show critical<BR>sector distances beyond which a change in contingency policy will yield benefits.<BR>Contingency Fuel - A320-214<BR>0<BR>100<BR>200<BR>300<BR>400<BR>500<BR>600<BR>700<BR>800<BR>900<BR>1000<BR>500 1000 1500 2000 2500 3000<BR>Sector Distance - nm<BR>Fuel - kg<BR>Minimum - 5 min Hold at 1500ft<BR>15 min Hold at 1500ft<BR>20 min trip fuel<BR>3% trip fuel<BR>5% trip fuel<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 16 -<BR>One further method of reducing the contingency fuel is by using a Decision<BR>Point or Redispatch Procedure. This involves the selection of a decision point<BR>where the aircraft can either continue to the destination as the remaining fuel is<BR>sufficient, or it can reach a suitable proximate diversion airport. More details are<BR>given in “Getting to Grips with Aircraft Performance”.<BR>To minimize the alternate fuel, the alternate airports should be chosen as<BR>near as possible to the destination.<BR>Both the JAA and FAA do not require the alternate fuel reserve in certain<BR>cases, depending on meteorological conditions and the suitability of the airport.<BR>More details are given in “Getting to Grips with Aircraft Performance”.<BR>Another part of the reserves is the extra fuel, which is at the Captain’s<BR>discretion.<BR>There are many reasons why this extra fuel is necessary. It could be due to<BR>uncertain weather conditions or availability of alternate and destination airfields,<BR>leading to a probability of re-routing. However it is often due to lack of confidence<BR>in the flight planning and the natural desire to increase reserves.<BR>This is the one area where a significant impact can be made through<BR>accurate flight planning. With this in place, the aircrew will see that the flight<BR>plans fuel burns are being achieved in practice. They will realize that the planned<BR>reserves are adequate and that there is no need for more.<BR>Contingency Fuel - A340-642<BR>0<BR>1000<BR>2000<BR>3000<BR>4000<BR>5000<BR>6000<BR>7000<BR>2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000<BR>Sector Distance - nm<BR>Fuel - kg<BR>Minimum - 5 min Hold at 1500ft<BR>15 min Hold at 1500ft<BR>20 min trip fuel<BR>5% trip fuel<BR>3% trip fuel<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 17 -<BR>4.4 TAXIING<BR>Good estimate of taxi times are required. Actual times need to be<BR>monitored and standard estimates changed as necessary. Jet engine performance<BR>is optimised for flight conditions, but all aircraft spend considerable time on the<BR>ground taxiing from the terminal out to the runway and back. This time has<BR>increased due to airport congestion, and increased airport size. This all leads to a<BR>waste of precious time and fuel.<BR>Only using one engine for taxiing twin-engine aircraft, or two engines for<BR>four-engine aircraft can give benefits in fuel burn. Such procedures need to be<BR>considered carefully, and operators have to define their field of application.<BR>Airbus provides standard procedures in the Flight Crew Operating Manual<BR>(FCOM) for such operations. The following factors regarding one or two engine out<BR>taxi should be considered carefully prior to its incorporation in the operators<BR>standard operating procedures:<BR>1. This procedure is not recommended for high gross weights<BR>2. This procedure is not recommended for uphill slopes or slippery<BR>runways<BR>3. No fire protection from ground staff is available when starting engine<BR>(s) away from the ramp<BR>4. Reduced redundancy increases the risk of loss of braking capability and<BR>nose wheel steering.<BR>5. FCOM procedures require not less than a defined time (from 2 to 5<BR>minutes depending on the engine) to start the other engine(s) before<BR>take off. On engines with a high bypass ratio, warm-up time prior to<BR>applying maximum take off thrust has a significant effect on engine<BR>life.<BR>6. Mechanical problems can occur during start up of the other engine(s),<BR>requiring a gate return for maintenance and delaying departure time.<BR>7. FCOM procedures require APU start before shutting down the engine<BR>after landing, to avoid an electrical transient.<BR>8. FCOM procedures require not less than a defined time before shutting<BR>down the other engine(s) after landing. On engines with a high bypass<BR>ratio, the cool-down time after reverse operation, prior to shut down<BR>has a significant effect on engine life.<BR>9. If an operator decides to use one or two engine out taxi, then FCOM<BR>recommendations about which engine(s) to use should be followed.<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 18 -<BR>As engine-out taxi requires more thrust per engine to taxi and maneuver,<BR>caution must be exercised to avoid excessive jet blast and FOD. More thrust is<BR>necessary for breakaways and 180 degrees turns.<BR>On twin-engine aircraft slow and/or tight taxi turns in the direction of the<BR>operating engine may not be possible at high gross weight.<BR>Single engine taxi may also be considered at low weights to avoid<BR>excessive use of the brakes to control the acceleration tendency with all engines.<BR>This brake use would be detrimental to carbon brake life.<BR>The following table gives an indication of the advantages of engine out taxi<BR>for 8 of the 12 minutes total taxi time, leaving 4 minutes warm up time.<BR>Fuel savings with Engine out taxi<BR>Aircraft types 12 minutes taxi<BR>(all engines)<BR>12 minutes taxi<BR>(8 with engine out)<BR>Engine Out taxi<BR>savings<BR>A300-600 300kg 200kg 100kg<BR>A310 240kg 160kg 80kg<BR>A318 120kg 80kg 40kg<BR>A319 120kg 80kg 40kg<BR>A320 138kg 92kg 46kg<BR>A321 162kg 108kg 54kg<BR>A330 300kg 200kg 100kg<BR>A340-200/300 300kg 200kg 100kg<BR>A340-500/600 420kg 280kg 140kg<BR>For engine out or all engines taxi, the use of a slow taxi speed<BR>costs fuel and time. A burst of power should be used to get the aircraft to<BR>taxi speed, then the power should be reduced to idle. However 30kt should<BR>not be exceeded.<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 19 -<BR>4.5 FUEL FOR TRANSPORTATION<BR>The normal message regarding fuel burn is that it is more economical to carry<BR>the minimum amount required for the sector. However there are occasions<BR>when it is economic to carry more fuel. This is when the price of fuel at the<BR>destination airfield is significantly higher than the price at the departure<BR>airfield.<BR>However, since the extra fuel on board leads to an increase in fuel<BR>consumption the breakeven point must be carefully determined.<BR>K is the transport coefficient:<BR>The addition of one tonne to the landing weight, means an addition of K<BR>tonnes to the take-off weight.<BR>For example, if K=1.3 and 1300 kg fuel is added at the departure, 1000 kg<BR>of this fuel amount will remain at the destination. So carrying one tonne of fuel<BR>costs 300 kg fuel more.<BR>The extra-cost of the loaded fuel at departure is<BR>Fuel weight x departure fuel price (ΔTOW x Pd = ΔLW x K x Pd)<BR>The cost saving of the transported fuel is<BR>Transported fuel x arrival price (ΔLW x Pa)<BR>The cost due to a possible increase in flight time is<BR>Flight time increase x cost per hour (ΔT x Ch)<BR>It is profitable to carry extra fuel if the cost saving exceeds the extra fuel loaded<BR>cost plus the extra time cost.<BR>(ΔLW x Pa) &gt;(ΔLW x K x Pd) + (ΔT x Ch)<BR>That is to say:<BR>ΔLW ( Pa - K x Pd) - (ΔT x Ch) &gt; 0<BR>LW<BR>K TOW<BR>Δ<BR>= Δ<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 20 -<BR>Therefore, if ΔT=0, it is profitable to carry extra fuel if the arrival fuel price to<BR>departure fuel price ratio is higher than the transport coefficient K.<BR>Pa &gt; K<BR>Pd<BR>Thus carrying extra fuel may be of value when a fuel price differential exists<BR>between two airports. Graphs in the FCOM assist in determining the optimum fuel<BR>quantity to be carried as a function of initial take-off weight (without additional<BR>fuel), stage length, cruise flight level and fuel price ratio. The following graph is<BR>an example for an A320.<BR>However the needs for accurate fuel planning is necessary to avoid arriving at the<BR>destination airport overweight. This could result in the economic benefit being<BR>eroded or negated due to extra hold time or circuits.<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 21 -<BR>4.6 AUXILIARY POWER UNIT<BR>The Auxiliary Power Unit (A.P.U.) is a self-contained unit which<BR>makes the aircraft independent of external pneumatic and electrical power supply<BR>and environmental conditioning.<BR>A.P.U. fuel consumption obviously represents very little in comparison with<BR>the amount of fuel for the whole aircraft mission. Nevertheless, operators have to<BR>be aware that adopting specific procedures on ramp operations can help save fuel<BR>and money.<BR>On the ground, A.P.U. fuel consumption depends on the A.P.U.<BR>type load and the ambient conditions. The minimum is when the APU is in the<BR>RTL(ready to load) condition. As additional loads, such as Electrical Loads(EL) and<BR>Environmental Conditioning System (ECS), are connected, the fuel consumption<BR>increases as shown in the following table (ISA, SL conditions).<BR>Aircraft Type APU<BR>Model<BR>RTL RTL<BR>Max EL<BR>Min ECS<BR>Max EL<BR>Max ECS<BR>Max EL<BR>A320 family 36-300 70 kg/hr 85 kg/hr 105 kg/hr 125 kg/hr<BR>A320 Family 131-9A 75 kg/hr 95 kg/hr 115 kg/hr 125 kg/hr<BR>A330, A340 331-350 120 kg/hr 140 kg/hr 175 kg/hr 210 kg/hr<BR>A340-500/600 331-600 160 kg/hr 180 kg/hr 225 kg/hr 290 kg/hr<BR>A.P.U. specific procedures to save fuel have to be defined by the<BR>operators. One extra minute of A.P.U. operation per flight at 180 kg/hr fuel flow,<BR>means an additional 3000 kg per year per aircraft. This will also result in<BR>increased maintenance costs.<BR>They have to choose between using ground equipment (Ground Power Unit,<BR>Ground Climatisation Unit, Air Start Unit) and the A.P.U. This choice depends on<BR>several parameters and each operator needs to determine the benefits at each<BR>airport and at each turnaround.<BR>Such parameters can include length of turnaround, ambient conditions, cost<BR>of ground connections, time delay to get connected, suitability and quality of<BR>ground equipment, passenger load, local noise restrictions, etc.<BR>For a long turnaround or night stop the G.P.U. is the best choice as time<BR>considerations are not prevailing. It saves both fuel and A.P.U. life. So operators<BR>are advised to use ground equipment if of a good quality, and to try to conclude<BR>agreements with airport suppliers to get preferential prices.<BR>However, for a short turnaround (45 minutes on average), the use of<BR>A.P.U. may be preferable to limit A.P.U. start cycles and improve reliability, even<BR>if it is not fully used during the turnaround. It is better to operate with A.P.U. at<BR>RTL than to shut it down and perform a new start cycle soon after shut down.<BR>Lack of suitable ground power may also require the use of APU. The use of APU<BR>4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 22 -<BR>may also be preferable to avoid excessive hook up charges or to reduce<BR>turnaround time.<BR>Some airport regulations restrict the use of the APU to a defined time prior to<BR>departure time and after the arrival.<BR>For extremely short turnarounds, complete engine shut down would have<BR>a cyclic cost impact, and therefore the turnaround could be made without APU.<BR>However a main engine can sometimes not meet the ECS demand in high load<BR>conditions (hot days).<BR>The disconnection of ground equipment supplies and the start of A.P.U. must<BR>be coordinated with A.T.C. pushback/slot requirements. A one-minute<BR>anticipation in each A.P.U. start will lead to a significant amount of fuel saving<BR>during a year (2000 to 4000 kg depending on A.P.U. types).<BR>Engine start up should also, if possible, be carefully planned in conjunction<BR>with A.T.C. If pushback is delayed, it is preferable to wait and use A.P.U. for air<BR>conditioning and electrical requirements. Engine start time is critical, and the<BR>engines should not be started until ready to go.<BR>The following table assuming typical engine fuel flows, shows extra fuel<BR>consumption by using one engine instead of the A.P.U. for 1 minute, assuming<BR>maximum electrical load and minimum ECS:<BR>Extra fuel when using Engine instead of APU<BR>Aircraft Type A.P.U. type<BR>Engine FF<BR>kg/hr/eng<BR>APU FF<BR>kg/hr<BR>Extra Fuel for<BR>1 minute<BR>A300 GE 331-250 520 150kg 6kg<BR>A310 GE 331-250 520 150kg 6kg<BR>A320 family CFM 36-300 300 105kg 3kg<BR>A330 GE 331-350 520 175kg 6kg<BR>A330 RR 331-350 720 175kg 9kg<BR>A340 CFM 331-350 300 175kg 2kg<BR>A340 RR 331-600 480 275kg 4kg<BR>In overall economic terms, the benefits of APU operation are not just<BR>confined to fuel usage. The hourly maintenance costs of an APU are cheaper than<BR>the aircraft powerplant, so reducing ground running time on the engines can<BR>significantly reduce the operating costs.<BR>Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES<BR>- 23 -<BR>4.7 AERODYNAMIC DETERIORATION<BR>Some of the most severe penalties in terms of fuel consumption are caused by<BR>increased drag resulting from poor airframe condition. Normal aerodynamic<BR>deterioration of an aircraft over a period of time can include the incomplete<BR>retraction of moving surfaces, damaged seals on control surfaces, skin roughness<BR>and deformation due to bird strikes or damage caused by ground vehicles,<BR>chipped paint, mismatched doors and excessive gaps. Each deterioration incurs a<BR>drag increase, and this increased drag is accompanied by increased fuel<BR>consumption.<BR>This subject is covered fully in the brochure “Getting Hands-On Experience with<BR>Aerodynamic Deterioration”.<BR>The following table gives the highest deterioration effect in each category for the<BR>three aircraft families as increased sector fuel consumption in Kg, based on typical<BR>utilization figures.<BR>Category Condition A300/310 A320<BR>Family<BR>A330/340<BR>Misrigging Slat 15mm 90 60 270<BR>Absence of Seals Flap (chordwise) 30 14 90<BR>Missing Part<BR>(CDL)<BR>Access Door 50 13 150<BR>Mismatched<BR>Surface<BR>Fwd Cargo Door<BR>10mm step for<BR>1m<BR>20 11 80<BR>Door seal leakage Fwd Pax Door<BR>5cm<BR>2 1 5<BR>Skin Roughness 1 m2 21 13 105<BR>Skin Dents Single 2 1 2<BR>Butt joint gaps Unfilled 0.2 0.1 0.6<BR>Butt Joint Gaps Overfilled 3 2 7<BR>External Patches 1 m2 3mm high 6 3 16<BR>Paint Peeling 1 m2 leading<BR>edge slat<BR>12 8 57<BR>Sector Distance 2000nm 1000nm 4000/6000nm<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 24 -<BR>5. IN FLIGHT PROCEDURES<BR>When an aircraft arrives at the end of the runway for take-off, it is the<BR>flying techniques (speed, altitude, configuration, etc) that have the biggest<BR>influence on fuel economy. Disciplined flight crews adhering to a flight plan based<BR>on the operator’s priorities can save much fuel and/or costs.<BR>This part intends to give recommendations to flight crews on the means to<BR>save fuel during the flight. It reviews the different phases of the flight, that is to<BR>say:<BR>• Take-off and Initial Climb<BR>• Climb<BR>• Cruise<BR>• Descent<BR>• Holding<BR>• Approach<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 25 -<BR>5.1 TAKE-OFF AND INITIAL CLIMB<BR>5.1.1 INTRODUCTION<BR>There are many variations in take-off technique that can directly affect the<BR>fuel burn. In general the effects are very dependent on the airframe/engine<BR>combination as well as aircraft weight, airfield altitude and temperature. The<BR>following fuel effects are representative values.<BR>5.1.2 BLEEDS<BR>For take-off, full bleeds can be used or one can consider selecting packs off<BR>or APU bleed on to improve take-off performance. Selecting packs off without<BR>APU will also improve fuel burn. The normal procedure would then be to select<BR>pack 1 on after climb thrust is selected and pack 2 on after flap retraction. This<BR>has the effect of reducing fuel burn by 2-3 kg on an A320 increasing to 5-10 kg<BR>on an A340-500/600.<BR>With APU bleed the engine fuel burn will be decreased by the same amount.<BR>However with APU used from pushback with 12minutes taxi, the additional APU<BR>fuel burn is 30kg for an A320 and 60-70kg for an A340.<BR>In economic terms, the APU fuel and maintenance cost is largely offset due<BR>to decreased engine maintenance costs bleeds off (higher flex temp).<BR>5.1.3 CONFIGURATION<BR>This effect is very dependent on the variables mentioned in the introduction,<BR>plus the choice of VR and V2. However the trend is always the same , with high<BR>flap/slat configurations (more extended) using more fuel than the lowest setting.<BR>Typical penalties/takeoff of higher flap settings compared with the low flap<BR>settings Conf 1+F are shown below (note that for the A300/A310 Conf 1+F, Conf<BR>2 and Conf 3 corresponds to the Flap 0,15 and 20 configuration respectively).<BR>Aircraft Conf 2 Conf 3<BR>A300/A310 1- 5kg 15kg<BR>A320 3-5kg 8-13kg<BR>A330 12kg 24kg<BR>A340 30kg 50kg<BR>These figures assume Full take-off thrust. The advantage of Conf 1+F<BR>increase with reduced power take-offs.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 26 -<BR>5.1.4 SPEEDS<BR>During a non limiting full power take-off, the use of the higher speeds<BR>appropriate to flex thrust instead of optimized speeds appropriate to the actual<BR>temperature can reduce the fuel burn by up to 8kg.<BR>5.1.5 FLEX THRUST<BR>Compared to a full thrust take-off, flex thrust will generally increase fuel<BR>burn. The increased time at low level offsets the slight reduction in fuel flow<BR>induced by the lower thrust. Typical increases are as follows:<BR>Aircraft Conf 1+F Conf 2 Conf 3<BR>A300/A310 10kg 10kg 10kg<BR>A320 1kg 5kg 5kg<BR>A330 0 0 0<BR>A340 5kg 20kg 25kg<BR>5.1.6 NOISE FLIGHT PATHS<BR>The effect of an ICAO type A noise flight path, with climb thrust selected at<BR>800ft and clean up delayed until 3000ft is generally to increase fuel burn<BR>compared to the standard take-off with power reduced at 1500ft. The actual<BR>distance to a fixed height, say 5000ft, varies very little with configuration. The<BR>main effect is the different altitude – speed history experienced by the engines.<BR>Typical values are as follows:<BR>Aircraft Conf 1+F Conf 2 Conf 3<BR>A320 -4kg +5kg +2kg<BR>A330 +100kg +100kg +115kg<BR>A340 +90kg +130kg +125kg<BR>5.1.7 COURSE REVERSAL<BR>In the event that a course reversal is required after take-off, then much<BR>distance can be saved using a lower initial climb speed. Suppose ATC require an<BR>aircraft to maintain runway heading to 6000ft. A lower climb speed will achieve<BR>this altitude earlier and thus reduce the ground distance and fuel burnt.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 27 -<BR>5.2 CLIMB<BR>5.2.1 INTRODUCTION<BR>Depending on speed laws, the climb profiles change. The higher the speed,<BR>the lower the climb path, the longer the climb distance.<BR>Climb profiles<BR>Climbs are normally performed in three phases on a constant IAS/Mach climb<BR>speed schedule at max climb thrust, as follows:<BR>• 250 KT indicated air speed (IAS) is maintained until flight level 100, then<BR>the aircraft accelerates to the chosen indicated air speed (e.g. “300kts);<BR>• constant indicated air speed is maintained until the crossover altitude;<BR>• constant Mach number is maintained until top of climb;<BR>Cruise level<BR>High speed<BR>Low speed<BR>Typical Climb Law<BR>0<BR>5000<BR>10000<BR>15000<BR>20000<BR>25000<BR>30000<BR>35000<BR>40000<BR>45000<BR>200 250 300 350 400 450 500<BR>Speed - ktas<BR>Altitude - ft<BR>Crossover<BR>altitude<BR>Tropopause<BR>250 kias<BR>300 kias<BR>M No 0.8<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 28 -<BR>The crossover altitude is the altitude where we switch from constant IAS<BR>climb to the constant Mach number climb. It only depends on the chosen IAS and<BR>Mach number, and does not depend on ISA variation.<BR>During climb, at constant IAS, the true air speed (TAS) and the Mach<BR>number increase. Then, during climb at constant Mach number, the TAS and the<BR>IAS decrease until the tropopause.<BR>To correctly evaluate the effects of climb techniques, climb and cruise flight<BR>must be viewed in relation to each other. A short climb distance for example<BR>extends the cruise distance; a low climb speed requires more acceleration to<BR>cruise speed at an unfavourable high altitude. One has therefore to consider<BR>sectors that cover acceleration to climb speed, climb, acceleration to cruise speed<BR>and a small portion of the cruise to the same distance.<BR>5.2.2 THE EFFECT OF CLIMB TECHNIQUE ON FUEL BURN<BR>This evaluation has been made for all Airbus types, based on a climb to<BR>35000ft, acceleration and cruise to a fixed distance. The assumed cruise speed<BR>was 0.78 for the A320 family and 0.8 for the rest.<BR>The reference climb technique is the standard technique given in each FCOM,<BR>and is summarized below:<BR>Aircraft types Speed law<BR>A300-600 250kts/300kts/M0.78<BR>A310 (GE) 250kts/300kts/M0.79<BR>A310 (PW) 250kts/300kts/M0.80<BR>A318/A319/A320/A321 250kts/300kts/M0.78<BR>A330 250kts/300kts/M0.80<BR>A340-200/300 250kts/300kts/M0.78<BR>A340-500/600 250kts/320kts/M0.82<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 29 -<BR>The following chart shows the variation of fuel burn with climb technique<BR>over a given climb + cruise distance.<BR>This shows that there is an optimum climb speed and max climb Mach<BR>number that produces the lowest fuel burn. This happens to be the standard<BR>technique (300kt/0.78). Climbing at 320kt/0.82 will burn 1% more fuel.<BR>However the following chart shows that this is obtained at the expense of<BR>time.<BR>Effect of Climb Technique on Fuel to 120nm<BR>A300B4-605R ISA F/L 350 Weight 140000kg<BR>-0.2%<BR>0.0%<BR>0.2%<BR>0.4%<BR>0.6%<BR>0.8%<BR>1.0%<BR>1.2%<BR>1.4%<BR>1.6%<BR>260 270 280 290 300 310 320 330 340 350<BR>Climb Speed - kias<BR>Fuel difference - %<BR>0.76<BR>0.78<BR>0.80<BR>Mach No<BR>FMG<BR>0.82<BR>CI "0"<BR>CI "100"<BR>Effect of Climb Technique on Time to 120nm<BR>A300B4-605R ISA F/L 350 Weight 140000kg<BR>-4%<BR>-3%<BR>-2%<BR>-1%<BR>0%<BR>1%<BR>2%<BR>3%<BR>4%<BR>5%<BR>6%<BR>260 270 280 290 300 310 320 330 340 350<BR>Climb Speed - kias<BR>Time difference - %<BR>0.80<BR>0.78<BR>0.76<BR>Mach No<BR>FMGS<BR>0.82<BR>CI "0"<BR>CI "100"<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 30 -<BR>This time difference plot has the same characteristics for all Airbus aircraft,<BR>with the best time being obtained at the highest climb speed and max climb Mach<BR>number. Note that although a slow climb speed gets the aircraft to cruise altitude<BR>earlier, this requires more acceleration to cruise speed and more cruise to a given<BR>distance, making it slower overall.<BR>The fuel difference plot characteristics vary with aircraft type. The A310,<BR>A321 and A330 show similar characteristics to the A300 with a best fuel climb<BR>speed of about 290 to 300 knots.<BR>The A318, A319 and A320 show better fuel burn at the lower speed range<BR>(260 to 280 knots)<BR>The A340 shows better fuel burn at the higher speed range (310-330 knots).<BR>The A310 and A340 are similar to the A300 in showing minimum fuel at a<BR>max climb Mach number of 0.78. In fact 0.8 is better for the A340-500/600.<BR>However the A320 family and A330 benefit from the lower Mach No of 0.76.<BR>Thus the A320 family benefits from low climb speeds and the A340 from high<BR>climb speeds. This difference arises from the different behavior during climb of<BR>twin-engine and four-engine aircraft. Indeed, twin-engine aircraft have a higher<BR>thrust than four engine aircraft, as they must satisfy some take-off climb<BR>requirements with only one engine operative, compared with 3 engines operative<BR>on the quads. This enables them to have a higher rate of climb than four engine<BR>aircraft and reach cruise flight levels quicker.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 31 -<BR>5.2.3 CORRELATION OF FUEL BURN &amp; TIME WITH CLIMB TECHNIQUE<BR>The following chart shows the differences in fuel and time to climb and<BR>cruise to a fixed distance with varying climb speed and max climb Mach number<BR>relative to the standard technique.<BR>This chart shows that the fastest technique (330/0.82) uses the least time<BR>(-3.2%) and the most fuel (+1.5%) whereas the slowest technique (270/0.76)<BR>uses the most time (+4.5%) and nearly the most fuel (+1.4%). The least fuel is<BR>obtained using a 300/0.78 climb technique. Variation of climb technique can cause<BR>a total variation of 1.5% and climb time by 8% for this aircraft.<BR>Also plotted on the charts are lines representing the speeds selected by the<BR>FMGS for various cost indices (CI). The left hand point of each line represents a CI<BR>of zero (fuel cost priority) and the right hand point represents a CI of 100 (flight<BR>time priority). It should be noted how the FMGS line approximates to the lower<BR>boundary of the time - fuel difference plot.<BR>The chart on the following page is for the A320 and shows completely<BR>different characteristics.<BR>Effect of Climb Technique on fuel and time to 120nm<BR>A300B4-605R ISA F/L 350 Weight 140000kg<BR>-6%<BR>-4%<BR>-2%<BR>0%<BR>2%<BR>4%<BR>6%<BR>-1% 0% 1% 2% 3%<BR>Fuel %<BR>Time %<BR>Mach No<BR>FMGS<BR>0.76<BR>0.78<BR>0.8<BR>280<BR>300<BR>320<BR>330<BR>Climb Speed<BR>KIAS<BR>0.82 270<BR>50kg<BR>1 minute<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 32 -<BR>The different mach numbers all coalesce together and the FMGS line forms the<BR>common boundary. Climb speed increases from the left to the right. Least fuel is<BR>obtained using a 0.76/280 technique. Mach No has little influence, but increasing<BR>speed from 280 to 330kias decreases time by 6% and increases fuel by 6%.<BR>Completely different characteristics are also shown in the next chart (A340-642).<BR>Effect of Climb Technique on fuel and time to 200nm<BR>A320-214 ISA F/L 350 Weight 70000kg<BR>-6%<BR>-4%<BR>-2%<BR>0%<BR>2%<BR>4%<BR>6%<BR>-2% -1% 0% 1% 2% 3% 4% 5% 6%<BR>Fuel %<BR>Time %<BR>Mach No<BR>FMGS<BR>0.76<BR>0.8<BR>100 kg<BR>1 minute<BR>270 kias<BR>280 kias<BR>300 kias<BR>320 kias<BR>330 kias<BR>Effect of Climb Technique on fuel and time to 160nm<BR>A340-642 ISA F/L 350 Weight 320000kg<BR>-2%<BR>0%<BR>2%<BR>4%<BR>6%<BR>8%<BR>10%<BR>-1% 0% 1% 2% 3% 4% 5%<BR>Fuel %<BR>Time %<BR>Mach No<BR>FMGS<BR>0.76<BR>0.78<BR>0.8<BR>0.82 100kg<BR>1 minute<BR>270 kias<BR>280 kias<BR>300 kias<BR>320 kias<BR>330 kias<BR>Climb<BR>Speed<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 33 -<BR>This shows a common technique is good for both fuel burn and time. The optimum<BR>is 320/0.80. There is little Mach No effect, but reducing the speed to 270 kias will<BR>increase fuel by 4% and time by 8%. Because the optimum technique is good for<BR>both fuel and time, there is a single FMGS point for all cost indeces.<BR>Earlier versions of the A340 showed that some marginal time benefit could be<BR>gained by climbing faster. However this would have affected the flight levels<BR>achieved. Consequently there is no variation of FMGS climb speed with cost index<BR>for all the A340 family.<BR>Appendix A presents some examples of time - fuel charts for other Airbus aircraft.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 34 -<BR>5.2.4 CLIMB TECHNIQUE COMPARISON TABLES<BR>The following tables show, for various Airbus aircraft, the climb time and<BR>fuel variations for a fixed distance, to FL 350, relative to a 300kias reference<BR>speed.<BR>Effect of Climb Speed on Fuel<BR>Effect of Climb Speed on Time<BR>It can be seen from the tables how the optimum techniques are very<BR>dependant on the aircraft type, and that a 10kt climb speed change can have a<BR>significant impact.<BR>Aircraft Climb ΔFuel – kg<BR>Mach No. 270KT 280 KT 300 KT 320 KT 330 KT<BR>A300 0.78 +40 +15 0 +5 +10<BR>A310 0.79 +5 0 +5 +15<BR>A318/A319/A320 0.78 -15 0 +30 +70<BR>A321 0.78 -10 0 +25 +60<BR>A330 0.80 +15 +5 0 +20 +35<BR>A340–200 0.78 +45 +20 0 +10 +25<BR>A340-300 0.78 +105 +50 0 -5 +20<BR>A340-500/600 0.82 +135 0 -5 -10<BR>Aircraft Climb ΔTime – minutes<BR>Mach No. 270KT 280 KT 300 KT 320 KT 330 KT<BR>A300 0.78 +0.8 +0.5 0 -0.3 -0.4<BR>A310 0.79 +0.5 0 -0.5 -0.6<BR>A318/A319/A320 0.78 +0.5 0 -0.4 -0.8<BR>A321 0.78 +0.8 0 -0.6 -1.0<BR>A330 0.80 +0.9 +0.6 0 -0.4 -0.7<BR>A340–200 0.78 +1.4 +0.8 0 -0.6 -0.8<BR>A340-300 0.78 +1.5 +0.9 0 -0.6 -1.0<BR>A340-500/600 0.82 +0.8 0 -0.6 -0.8<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 35 -<BR>5.2.5 DERATED CLIMB<BR>In order to reduce engine maintenance costs, there are derated climb<BR>options available on the A330 and A340 aircraft. There are two levels of derate,<BR>D1 and D2. At a certain altitude the derate is washed out such that at Max Climb<BR>rating is achieved generally before 30000ft. The following shows a typical derate<BR>thrust variation picture, but this will vary with engine and temperature.<BR>However this derate will result in more fuel and time required to reach the<BR>same distance. The effect is dependant on aircraft weight, temperature and cruise<BR>flight level. The following table gives some typical penalties in ISA conditions to<BR>35000ft.<BR>Derate D1 Derate D2<BR>Aircraft Weight<BR>(kg)<BR>Fuel<BR>Increase<BR>Time<BR>Increase<BR>Fuel<BR>Increase<BR>Time<BR>Increase<BR>A330-203 190000 5kg 0.5 min 20kg 0.6 min<BR>A330-223 190000 20kg 0.2 min 40kg 0.5 min<BR>A330-343 190000 20kg 0.2 min 40kg 0.5 min<BR>A340-212 240000 65kg 0.9 min 120kg 1.5 min<BR>A340-313 240000 140kg 0.8 min 225kg 1.4 min<BR>A340-313E 240000 140kg 1.0 min 335kg 1.4 min<BR>A340-642 340000 270kg 0.6 min 445kg 1.0 min<BR>Derated Climb - Net Thrust Reduction<BR>-25<BR>-20<BR>-15<BR>-10<BR>-5<BR>0<BR>0 10000 20000 30000 40000<BR>Altitude / ft<BR>Net Thrust Difference to MCL %<BR>Derated Climb 1<BR>Derated Climb 2<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 36 -<BR>5.3 CRUISE<BR>5.3.1 INTRODUCTION<BR>The cruise phase is the most important phase regarding fuel savings. As it is<BR>the longest for long haul aircraft, it is possible to save a lot of fuel. So discipline<BR>must be exercised particularly in this phase.<BR>The two variables that most influence cruise fuel consumption are the cruise<BR>speed (IAS or Mach Number) and the altitude or flight level. The following shows<BR>their influence on a single sector assuming standard climb and descent<BR>procedures.<BR>The correct selection of the cruise parameters is therefore fundamental in<BR>minimizing fuel or operating cost. This chart shows the normal laws that aircraft<BR>consume less fuel when flown slower or when flown higher. However there are<BR>limits to these laws. Flying lower than the maximum range speed will increase the<BR>block fuel, as will flying higher than an optimum altitude.<BR>Block Fuel and Time for various Flight Levels and Mach numbers<BR>A330-223 ISA 3000nm Payload 30000kg JAR Reserves<BR>35000<BR>37000<BR>39000<BR>41000<BR>43000<BR>45000<BR>360 380 400 420 440 460 480 500 520 540 560<BR>Block Time - minutes<BR>Block Fuel - kg<BR>Green Dot<BR>Max Speed<BR>Range<BR>Long<BR>Range<BR>M 0.78<BR>M 0.80<BR>M 0.82<BR>Flight<BR>Level<BR>250<BR>270<BR>290<BR>310<BR>330<BR>350<BR>370<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 37 -<BR>5.3.2 CRUISE ALTITUDE OPTIMISATION<BR>In examining SR changes with the altitude at a constant Mach number, it is<BR>apparent that, for each weight, there is an altitude where SR is maximum. This<BR>altitude is referred to as “optimum altitude”.<BR>Optimum Altitude Determination at Constant Mach Number<BR>When the aircraft flies at the optimum altitude, it is operated at<BR>the maximum lift to drag ratio corresponding to the selected Mach number.<BR>High Speed Polar Curve<BR>When the aircraft flies at high speed, the polar curve depends on the indicated Mach<BR>number, and decreases when Mach increases. So, for each Mach number, there is a different<BR>value of (CL/CD)max, that is lower as the Mach number increases.<BR>M=0.84<BR>M = 0.82<BR>M = 0.86<BR>M &lt;0.76<BR>Pressure<BR>Altitude<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 38 -<BR>When the aircraft is cruising at the optimum altitude for a given Mach, CL is<BR>fixed and corresponds to (CL/CD)max of the selected Mach number. As a result,<BR>variable elements are weight and outside static pressure (Ps) of the optimum<BR>altitude. The formula expressing a cruise at optimum altitude is:<BR>constant<BR>P<BR>Weight<BR>s<BR>=<BR>In the FCOM Flight Planning Chapters the optimum altitude is<BR>shown on the Cruise Level chart for 2 or more speeds. This chart also shows the<BR>Maximum Altitudes as limited by performance and buffet. A typical FCOM chart<BR>showing the variation of optimum altitude with weight for one speed is shown<BR>below.<BR>It should be noted that the influence of airspeed on optimum altitude is not<BR>very significant in the range of normal cruise speeds.<BR>In order to minimize fuel burn, the aircraft should therefore be flown at the<BR>optimum altitude. However this is not always possible. Performance limitations<BR>such as rate of climb or available cruise thrust can lead to a maximum altitude<BR>below the optimum, as can buffet limitations. At low weights, the optimum<BR>altitude may be above the maximum certificated altitude. In addition, Air Traffic<BR>Control restrictions can affect the flown flight level.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 39 -<BR>The following table shows the specific range penalty of not flying at optimum<BR>altitude, assuming a cruise Mach No of 0.8. It should be noted that each<BR>airframe/engine combination has different values. It should be noted that these<BR>are average values and there are slight variations with different weight/optimum<BR>altitude combinations.<BR>Specific Range Penalty for not flying at Optimum Altitude<BR>Aircraft +2000ft -2000ft -4000ft -6000ft<BR>A300B4-605 2.0% 0.9% 3.4% 9.3%<BR>A310-324 1.9% 1.4% 4.4% 9.3%<BR>A318-111 0.7% 1.6% 5.0% 10.0%<BR>A319-132 1.0% 3.0% 7.2% 12.2%<BR>A320-211 ** 1.1% 4.7% 9.5%<BR>A320-232 1.4% 2.1% 6.2% 12.0%<BR>A321-112 2.3% 1.4% 4.6% 15.2%<BR>A330-203 1.8% 1.3% 4.2% 8.4%<BR>A330-343 3.0% 1.0% 3.2% 7.2%<BR>A340-212 1.4% 1.5% 4.0% 8.0%<BR>A340-313E 1.5% 1.6% 5.2% 9.5%<BR>A340-642 1.6% 0.6% 2.2% 5.1%<BR>** Above Maximum Altitude<BR>Generally if one flies within 2000ft of optimum altitude, then the specific<BR>range is within about 2% of the maximum. However fuel burn-off is an important<BR>consideration.<BR>Consider an A340-313E at a weight such that the optimum altitude is<BR>33000ft. If the aircraft flies at FL 310 the SR penalty is 2.1% for the weight<BR>considered. However after a fuel burn of 20800kg, during which the aircraft would<BR>have traveled 1400nm the optimum altitude increases to 35000ft and the penalty<BR>is now 5.2%.<BR>There is also an effect on block time due to the different altitudes. The true<BR>air speed increases/decreases 4kts, or just under 1% for each 2000ft lower/higher<BR>cruise altitude.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 40 -<BR>5.3.2.1 CROSS-OVER ALTITUDE VERSUS OPTIMUM ALTITUDE<BR>It has been previously shown that the TAS is the maximum at the crossover<BR>altitude. One can wonder whether it is profitable to stay at this altitude, instead of<BR>climbing to the first optimum altitude.<BR>Assuming the standard climb laws, the crossover altitude can be derived. The<BR>standard speed laws are tabulated in paragraph 5.2.2.<BR>The next table shows the effect of flying at the crossover altitude instead of<BR>optimum flight levels. The 1st optimum flight level has been chosen for the short<BR>sectors, whereas longer sectors assume step climbs with FL 310, 350 and 390<BR>being available. This assumes ISA conditions and a take-off weight for a typical<BR>sector with max passengers and some freight (2500kg for the A320 family and<BR>5000kg for the other aircraft).<BR>Aircraft type Sector<BR>Distance<BR>Cross-over<BR>altitude<BR>Optimum<BR>Flight Levels<BR>Gained<BR>time (min)<BR>Increase in fuel<BR>consumption<BR>A300B4-605R 2000nm 29000 ft 310/350 7 1190kg<BR>A310-324 2000nm 30000ft 350/390 3 2160kg<BR>A318-111 1000nm 29000 ft 370 3 740kg<BR>A319-112 1000nm 29000 ft 370 3 650kg<BR>A320-214 1000nm 29000 ft 350 2 580kg<BR>A320-232 1000nm 29000 ft 340 2 440kg<BR>A321-211 1000nm 29000 ft 330 2 350kg<BR>A330-203 4000nm 31000 ft 350/390 9 5040kg<BR>A330-223 4000nm 31000 ft 350/390 9 5780kg<BR>A330-343 4000nm 31000 ft 350/390 10 6380kg<BR>A340-212 6000nm 29000 ft 310/350/390 17 10900kg<BR>A340-313 6000nm 29000 ft 310/350/390 14 8410kg<BR>A340-313E 6000nm 29000 ft 310/350/390 17 9310kg<BR>A340-500/600 6000nm 29000 ft 310/350/390 18 2430kg<BR>This table shows that flying at crossover altitude increases the fuel burn<BR>significantly for a relatively small reduction in block time.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 41 -<BR>5.3.2.2 CRUISE OPTIMISATION WITH STEPPED CLIMB<BR>5.3.2.2.1 Introduction<BR>It has been shown that flying at non-optimum altitudes can cause significant<BR>fuel penalties, and that the effect of fuel burn is to increase the optimum altitude.<BR>The ideal scenario would be to follow the optimum altitude as in the climbing<BR>cruise, but A.T.C. constraints, performance and buffet limits do not make this<BR>possible. However, by changing the cruise level with step climbs, as the aircraft<BR>gets lighter the aircraft will remain as close as possible to the optimum altitude.<BR>5.3.2.2.2 Choice of Profile<BR>Several parameters such as weather conditions, ATC requirements, may<BR>influence any decision made by the crew with regard to three fundamental<BR>priorities: maneuverability, passenger comfort, and economics.<BR>This pertains to the choice of the cruise flight level that can be made<BR>according to the three following climb profiles as shown below for an A340-642:<BR>The Low profile initiates the step climb at the weight where the next<BR>available flight level is also the optimum flight level at that weight. Consequently<BR>the flight levels are always at or below the optimum. This has the advantage of<BR>better maneuverability margins and generally a better speed as it is closer to the<BR>crossover altitude.<BR>Step Climb Profiles<BR>Even Flight Levels Non RVSM<BR>26000<BR>28000<BR>30000<BR>32000<BR>34000<BR>36000<BR>38000<BR>40000<BR>42000<BR>0 1000 2000 3000 4000 5000 6000 7000 8000 9000<BR>Distance from Brake Release - nm<BR>Altitude - ft<BR>Low Profile<BR>Mid Profile<BR>High Profile<BR>Optimum Altitude<BR>Maximum Altitude<BR>Maximum Altitude Optimum<BR>Altitude<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 42 -<BR>The high profile initiates the step climb at the weight where the next<BR>available flight level is also the maximum flight level at that weight. The flight<BR>levels are mainly above the optimum and the aircraft will have decreased<BR>maneuverability and fly slower.<BR>The mid profile initiates the step climb at the weight where the specific<BR>range at the next available flight level is better than that at the current flight<BR>level. This enables the flight profile to remain as close as practically possible to<BR>the optimum flight level. It is this technique that is recommended for best fuel<BR>economy, and is also very close to that required for best economics.<BR>It is interesting to note that, in this case, the Mid profile step climb is made<BR>1140nm before the Low Profile step climb and 1520nm after the High profile step<BR>climb.<BR>The situation changes with odd flight levels:<BR>Because of the different available flight levels, the step climbs are initiated<BR>some 1500nm further than the even flight level step climb points. However the<BR>relative merits of each profile remains the same.<BR>With Reduced Vertical Separation Minima (RVSM) the difference between<BR>flight levels reduces from 4000 to 2000ft and this enables the aircraft profile to<BR>remain much closer to the optimum. In addition the high profile (depending on<BR>the aircraft) remains much higher than the optimum, increasing the fuel penalty.<BR>This profile is shown on the following page.<BR>Step Climb Profiles<BR>Odd Flight Levels Non RVSM<BR>26000<BR>28000<BR>30000<BR>32000<BR>34000<BR>36000<BR>38000<BR>40000<BR>42000<BR>0 1000 2000 3000 4000 5000 6000 7000 8000 9000<BR>Distance from Brake Release - nm<BR>Altitude - ft<BR>Low Profile<BR>Mid Profile<BR>High Profile<BR>Optimum Altitude<BR>Maximum Altitude<BR>Maximum Altitude Optimum<BR>Altitude<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 43 -<BR>Thus pilots are advised to perform step climbs around the optimum altitudes.<BR>To facilitate this, the optimum weight for climb to the next flight level is given in<BR>most FCOM’s (not A300/A310). An example is shown below.<BR>Step Climb Profiles<BR>Odd Flight Levels RVSM<BR>26000<BR>28000<BR>30000<BR>32000<BR>34000<BR>36000<BR>38000<BR>40000<BR>42000<BR>0 1000 2000 3000 4000 5000 6000 7000 8000 9000<BR>Distance from Brake Release - nm<BR>Altitude - ft<BR>Low Profile<BR>Mid Profile<BR>High Profile<BR>Optimum Altitude<BR>Maximum Altitude<BR>Maximum Altitude Optimum<BR>Altitude<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 44 -<BR>On all Airbus FMS-equipped aircraft, the optimum altitude (OPT FL) and<BR>the maximum flight level (MAX FL) are displayed on the MCDU progress page. The<BR>recommended maximum altitude in the FMGC ensures a 0.3g buffet margin, a<BR>minimum rate of climb of 300ft/min at MAX CLIMB thrust and a level flight at MAX<BR>CRUISE thrust. Depending on weight and type, it is 2000 to 4000ft above the<BR>optimum altitude.<BR>Typical cruise distances between 2000 foot altitude steps are shown in the<BR>following table:<BR>Type Distance - nm<BR>A300 1000 - 1100<BR>A310 1150 - 1250<BR>A320 1200 - 1300<BR>A330 1500 - 1650<BR>A340 1500 - 1650<BR>A340-500/600 1600 - 1700<BR>For sector lengths greater than these, where ATC restrictions do not allow a<BR>change in cruise altitude from the initial requested level, the initial request should<BR>be the highest compatible with the maximum cruise altitude.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 45 -<BR>5.3.2.3 DELAYS IN ALTITUDE CHANGES<BR>Let’s consider an aircraft that is at flight level 330, which has, at that weight,<BR>an optimum flight level of 370. If it does not climb to FL 370 for ATC or other<BR>reasons, it will consume more fuel. The following table shows the difference in fuel<BR>burn for a 500nm still air cruise, when cruising at FL 330 instead of FL 370.<BR>Aircraft<BR>Type<BR>Fuel Increase<BR>(kg)<BR>Fuel Increase<BR>(%)<BR>A300B4-605R 238 5.2<BR>A310-324 221 5.3<BR>A318-111 150 6.2<BR>A319-132 184 7.9<BR>A320-211 158 6.2<BR>A320-232 187 7.9<BR>A321-112 155 5.5<BR>A330-203 324 5.5<BR>A330-343 342 5.6<BR>A340-212 393 6.2<BR>A340-313E 378 6.0<BR>A340-500/600 336 4.1<BR>Thus delaying a climb to a higher altitude has a significant impact on fuel<BR>burn.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 46 -<BR>5.3.2.4 OPTIMUM ALTITUDES ON SHORT STAGES<BR>For short stages, the choice of cruise flight level is often restricted due to the<BR>necessary climb and descent distance. Airbus philosophy assumes a minimum 5<BR>minute cruise sector, because a climb followed immediately by the descent is not<BR>appreciated by pilots, passengers or ATC.<BR>If the stage length is of sufficient length that the optimum flight level can be<BR>reached, but the cruise is of short duration, then the benefits at this flight level<BR>will be marginal. It may even be worthwhile to cruise at one flight level lower, as<BR>the increased climb consumption offsets any reduced cruise consumption.<BR>In the FCOM there is a chart showing the optimum altitude on a short stage.<BR>An example is shown below.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 47 -<BR>5.3.3 CRUISE SPEED OPTIMISATION<BR>Having been given a flight level which may be a requested optimum altitude<BR>or one imposed by air traffic control, speed is the only remaining parameter that<BR>requires selection. The following picture shows the variation of Specific Range with<BR>Mach Number for different aircraft weights at a fixed altitude.<BR>The Mach number, which gives the best specific range, can be determined. It<BR>is called the maximum range cruise Mach (MMR). Nevertheless, for practical<BR>operations, a long-range cruise procedure is defined which gains a significant<BR>increase in speed compared to MMR with only a 1% loss in specific range. Like the<BR>MMR speed, the MLRC speed also decreases with decreasing weight, at constant<BR>altitude.<BR>A more detailed explanation of this can be found in “Getting to Grips with<BR>Aircraft Performance”<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 48 -<BR>The following chart shows the typical variation of the Long Range Cruise<BR>Mach Number with aircraft weight for various flight levels. Also plotted on this<BR>chart is the optimum altitude line. This shows that there is not much variation in<BR>the long-range cruise mach number at these altitudes.<BR>It would therefore be possible to fly a constant Mach number procedure<BR>instead of the variable LRC speed procedure. In order to save fuel however, the<BR>exact LRC speed should be maintained.<BR>Long Range Cruise Mach Number<BR>A330-243 ISA<BR>0.72<BR>0.74<BR>0.76<BR>0.78<BR>0.8<BR>0.82<BR>0.84<BR>160 170 180 190 200 210 220 230 240<BR>Aircraft Weight (1000kg)<BR>Mach Number<BR>270<BR>290<BR>310<BR>330<BR>350<BR>370<BR>390<BR>410<BR>Flight<BR>Optimum<BR>Altitude<BR>The Long Range Cruise Speed can be found in the Cruise tables in the FCOM.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 49 -<BR>5.3.4 WIND INFLUENCE<BR>Wind can have a significant influence on fuel burns. Nowadays,<BR>meteorological forecasts are very reliable and its integration into the FMS provides<BR>accurate information to crews. Hence the latter best perform flight planning with a<BR>view towards fuel savings.<BR>The effect of the wind on trip time and fuel is shown on the following chart,<BR>which gives fuel consumption and time for a 2000nm sector, with respect to flight<BR>levels, Mach number and wind (tailwind positive) for a fixed take-off weight.<BR>This plot graphically shows the magnitude of the significant changes in fuel<BR>consumption and time due to winds. FCOM Tables show the equivalent still air<BR>distances for any ground distance/wind combination.<BR>However the winds can affect the performance optimization as well as<BR>changing the effective still air distance. The MMR (or MLRC) value varies with<BR>headwind or tailwind, due to changes in the SR.<BR>The effect of a tailwind is to increase the ground speed, and therefore the<BR>SR, by the ratio of ground speed to airspeed. A given wind speed therefore has a<BR>larger effect at the lower airspeeds, which changes the optimum speed.<BR>A321<BR>FL 350<BR>FL 330<BR>FL 310<BR>FL 290<BR>FL 330<BR>FL 350<BR>FL 310<BR>FL 290<BR>11000<BR>12000<BR>13000<BR>14000<BR>15000<BR>16000<BR>17000<BR>18000<BR>3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 5.7<BR>Time (hour)<BR>Fuel consumption (kg)<BR>M 0.8<BR>M 0.78 M 0.76<BR>M 0.8<BR>M 0.78<BR>M 0.76<BR>M 0.8<BR>M 0.78<BR>M 0.76<BR>M 0.8<BR>M 0.78<BR>M 0.8 M 0.76<BR>M 0.78<BR>M 0.76<BR>-60 kts<BR>-30 kts<BR>30 kts<BR>60 kts<BR>0 kts<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 50 -<BR>The following chart shows the Maximum Range Mach number versus wind<BR>variations.<BR>MMR and wind influence<BR>This shows that<BR>Tailwinds increase the specific range and lower the speeds<BR>Headwinds decrease the specific range and raise the speeds.<BR>The wind speed can be different at different altitudes. For a given<BR>weight, when cruise altitude is lower than optimum altitude, the specific range<BR>decreases. Nevertheless, it is possible that, at a lower altitude with a favorable<BR>wind, the ground specific range improves. When the favorable wind difference<BR>between the optimum altitude and a lower one reaches a certain value, the<BR>ground-specific range at lower altitude is higher than the ground-specific range at<BR>optimum altitude. As a result, in such conditions, it is more economical to cruise<BR>at the lower altitude.<BR>There is information in the most FCOM’s (not A300/310) to indicate the<BR>amount of favorable wind, necessary to obtain the same ground-specific range at<BR>altitudes different from the optimum. If the wind is more favorable then it is<BR>beneficial to fly lower. The following shows such a page:<BR>Given weight<BR>and Pressure<BR>Altitude<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 51 -<BR>IN FLIGHT PERFORMANCE<BR>CRUISE<BR>3.05.15 P 7<BR>SEQ 020 REV 24<BR>WIND ALTITUDE TRADE FOR CONSTANT SPECIFIC RANGE<BR>GIVEN : Weight : 68000 kg (150 000 lb)<BR>Wind at FL350 : 10 kt head<BR>FIND : Minimum wind difference to descend to FL310 : (26 − 3) = 23 kt<BR>RESULTS : Descent to FL310 may be considered provided the tail wind at this<BR>altitude is more than (23 − 10) = 13 kt.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 52 -<BR>5.3.5 MANAGED MODE<BR>The flight management system (FMS) optimizes the flight plan for winds,<BR>operating costs and suggests the most economical cruise altitude and airspeed,<BR>depending on the cost index chosen by the airline. An airline that wants to save<BR>fuel has to choose a low cost index. The next part intends to highlight the impact<BR>of the cost index on fuel consumption and on trip time. More complete information<BR>can be found in the “Getting to Grips with Cost Index” brochure.<BR>5.3.5.1 ECONOMIC MACH NUMBER<BR>Long-range Cruise Mach number was considered as a minimum<BR>fuel regime. If we consider the Direct Operating Cost instead, the Economic<BR>Mach number (MECON), can be introduced.<BR>Direct Operating Costs (DOC) are made up of fixed, flight-time<BR>related and fuel-consumption related costs. As a result, for a given trip, DOC can<BR>be expressed as:<BR>DOC C C F C T C F T = + .Δ + .Δ<BR>where CC = fixed costs<BR>CF = cost of fuel unit ΔF = trip fuel<BR>CT = time related costs per flight hour ΔT = trip time<BR>As DOCs are calculated per nautical mile, it is possible to plot fuelrelated<BR>costs, flight-time related costs, and direct operating costs based on Mach<BR>number .<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 53 -<BR>Minimum fuel costs correspond to the Maximum Range Mach<BR>number. The minimum DOC corresponds to a specific Mach number, referred to as<BR>Econ Mach (MECON).<BR>ECON<BR>ECON<BR>weight constant FL M<BR>constant weight M<BR>= ⇒<BR>FL = ⇒<BR>&#1048778; &#1048778;<BR>&#1048780; &#1048780;<BR>The MECON value depends on the time and fuel cost ratio. This ratio is called<BR>cost index (CI), and is usually expressed in kg/min or 100lb/h:<BR>F<BR>T<BR>C<BR>C<BR>=<BR>Cost of fuel<BR>Cost Index (CI) = Cost of time<BR>Depending on the cost index, the predicted aircraft and atmospheric<BR>conditions, the optimum altitude and the economic Mach number are computed.<BR>From then on, fuel consumption depends only of the chosen cost index.<BR>The following chart shows the economic Mach number variation with flight<BR>level for different cost indices.<BR>This shows the general trend, common with all aircraft, of increasing<BR>economic Mach number with flight level.<BR>Economic Cruise Mach Number<BR>A310-324 ISA 130000kg<BR>0.73<BR>0.74<BR>0.75<BR>0.76<BR>0.77<BR>0.78<BR>0.79<BR>0.8<BR>0.81<BR>0.82<BR>290 300 310 320 330 340 350 360 370 380<BR>Flight Level<BR>ECON Mach<BR>Optimum<BR>F/L<BR>Maximum<BR>F/L<BR>0<BR>20<BR>40<BR>60<BR>80<BR>100<BR>Cost Index<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 54 -<BR>The charts also show large economic Mach number changes with flight<BR>level for low cost indices, whereas it is rather constant for high cost indices. The<BR>economic Mach is very sensitive to the cost index when flying below the optimum<BR>altitude.<BR>The effect of weight variation at a fixed flight level is shown below.<BR>The charts show that for high cost indices, the economic Mach number stays<BR>fairly constant throughout the flight. Nevertheless, for a low cost index, the<BR>economic Mach number reduces significantly as the weight reduces. This is quite<BR>normal as low cost indices favor fuel consumption at the expense of time.<BR>Moreover, we notice that for low cost indices, a small cost index increment has a<BR>far-reaching influence on the economic Mach number, and hence on flight time.<BR>These trends are typical of all aircraft.<BR>Economic Cruise Mach number<BR>A310-324 ISA F/L 350<BR>0.7<BR>0.72<BR>0.74<BR>0.76<BR>0.78<BR>0.8<BR>0.82<BR>90 95 100 105 110 115 120 125 130 135 140<BR>Aircraft Weight - tonnes<BR>ECON Mach<BR>0<BR>20<BR>40<BR>60<BR>80<BR>100<BR>Cost<BR>Index<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 55 -<BR>5.3.5.2 TIME/FUEL RELATIONSHIP<BR>To know whether the fuel economies at low cost indices are worthwhile, the<BR>impact of cost index on time has to be considered. The following graph show both<BR>trip fuel and time for different flight levels and cost indices. The shape of this<BR>chart is typical of all types.<BR>As it can be seen, it is not really advantageous to fly at very low cost indices<BR>as fuel savings are not significant compared to time loss. Although using slightly<BR>higher fuel, a slightly higher cost index gives significant time gains.<BR>For instance, for the A319, increasing the cost index from 0 to 20 reduces<BR>the block time by 15 minutes (5%) for a fuel burn increase of only 200kg (2%) on<BR>a 2000nm sector.<BR>A319<BR>FL390<BR>FL370<BR>FL350<BR>FL330<BR>FL310<BR>FL290<BR>FL390<BR>FL370<BR>FL350<BR>FL330<BR>FL310<BR>FL290<BR>FL390<BR>FL370<BR>FL350<BR>FL330<BR>FL310<BR>FL290<BR>9000<BR>9500<BR>10000<BR>10500<BR>11000<BR>11500<BR>12000<BR>12500<BR>13000<BR>4.2 4.4 4.6 4.8 5 5.2 5.4<BR>time (hours)<BR>fuel consumption (kg)<BR>CI=0<BR>CI=20<BR>CI=40<BR>CI=60<BR>CI&gt;100<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 56 -<BR>5.3.6 EFFECT OF SPEED INCREASE ON MANAGED MODE<BR>Flying at a given cost index rather than at a given Mach number provides the<BR>added advantage of always benefiting from the optimum Mach number as a<BR>function of aircraft gross weight, flight level and head/tailwind components.<BR>This means the ECON mode (“managed” mode) can save fuel relative to<BR>fixed Mach schedules (“selected” mode) and for an equivalent time.<BR>One can wonder whether selecting a higher Mach number than the one<BR>chosen by the FMS has a significant impact on fuel consumption. Imagine an<BR>aircraft flying at flight level 370, in managed mode and at the optimum weight of<BR>FL370. The FMS computes the optimum speed based on cost index, temperature<BR>and wind. If the pilot selects another (higher) Mach number, the fuel consumption<BR>will increase.<BR>The following tables show the effect of such a speed increase.<BR>We notice that although decreasing block times, the increase of Mach<BR>number above the Optimum speed can result in significant increases in fuel burn.<BR>Pilots hence have to be patient and should not change the Mach number even<BR>when under the impression that the aircraft does not fly fast enough.<BR>Moreover, when possible, the managed mode must be kept.<BR>Economic Mach No + 0.005 Economic Mach No + 0.01<BR>Fuel Penalty ΔTime Fuel Penalty ΔTime<BR>Aircraft Sector Kg % Min Kg % Min<BR>A300-605 2000 Nm 110 0.4 1 230 0.9 3<BR>A310-324 2000 Nm 90 0.4 1 430 2.0 8<BR>A318 1000 Nm 30 0.5 1 60 1.0 1<BR>A319 1000 Nm 20 0.2 1 40 0.6 2<BR>A320 1000 Nm 20 0.3 1 40 0.7 2<BR>A321 1000 Nm 10 0.1 1 30 0.4 1<BR>A330 4000 Nm 150 0.3 3 330 0.6 6<BR>A340-212 6000 Nm 390 0.5 5 790 0.9 10<BR>A340-313E 6000 Nm 380 0.4 5 900 1.0 10<BR>A340-500 6000 Nm 1050 0.9 5 2540 2.1 9<BR>A340-600 6000 Nm 820 0.7 4 2060 1.8 9<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 57 -<BR>5.4 DESCENT<BR>5.4.1 INTRODUCTION<BR>Depending on the descent law, flight paths do vary in steepness.<BR>Indeed, the higher the speed law, the steeper the flight path.<BR>Descent profiles.<BR>Descents are normally performed in three phases on a constant IAS/Mach<BR>descent speed schedule, as follows:<BR>• Constant Mach number is maintained until the crossover altitude<BR>• Constant indicated air speed is maintained down to 10000ft<BR>• 250 KT indicated air speed (IAS) is maintained below flight level 100, until<BR>the aircraft decelerates for landing<BR>The engine thrust is normally set to flight idle for the descent and the speed<BR>is controlled by the aircraft attitude. In these conditions higher weights increase<BR>the descent distance because of the reduction of descent gradient (which equals<BR>/weight in stabilized flight). This also increases the descent fuel.<BR>However a descent from high altitudes at low weight may lead to a gradient<BR>of descent that results in an excessive cabin rate of descent. In these cases the<BR>rate of descent is reduced by application of power, until a flight idle descent can<BR>be continued. This results in what is known as the re- pressurization segment, and<BR>this can reverse the weight-descent distance relationship.<BR>To correctly evaluate the effects of descent techniques, cruise and<BR>descent flight must be viewed in relation to each other. A short descent distance<BR>for example extends the cruise distance. One has therefore to consider in addition<BR>to the descent, a small portion of the cruise to the same distance.<BR>High speed<BR>Low speed<BR>Cruise level<BR>TOD<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 58 -<BR>5.4.2 THE EFFECT OF DESCENT TECHNIQUES ON FUEL BURN<BR>An evaluation has been made of the fuel burn to a constant distance, and<BR>this now shows that the higher weights use less fuel. Lower speeds, although<BR>requiring more fuel for the descent only requires less total fuel because of the<BR>longer descent distance. This is shown in the following chart.<BR>At a fixed weight, the following chart shows that the minimum fuel occurs<BR>at a descent speed of 240kias to 280kias, dependant on flight level.<BR>However there is a significant time penalty at these speeds.<BR>Effect of Descent Technique on Fuel and Climb for 115nm<BR>A310-324 ISA 110000Kg<BR>17.5<BR>18.0<BR>18.5<BR>19.0<BR>19.5<BR>20.0<BR>20.5<BR>21.0<BR>21.5<BR>300 350 400 450 500 550 600 650<BR>Fuel - kg<BR>Time - min<BR>240<BR>250<BR>260<BR>300<BR>320<BR>330<BR>3<BR>13<BR>33<BR>54<BR>74<BR>100<BR>390 370 Initi3a5l 0Flight Level330 310<BR>Cost<BR>Index<BR>Descent<BR>Speed KIAS<BR>280<BR>Effect of Descent technique on Fuel and Time for 115nm<BR>A310-324 ISA F/L 350<BR>17.5<BR>18.0<BR>18.5<BR>19.0<BR>19.5<BR>20.0<BR>20.5<BR>380 400 420 440 460 480 500 520 540<BR>Fuel - kg<BR>Time - min<BR>90t<BR>110t<BR>130t<BR>260<BR>280<BR>300<BR>320<BR>Aircraft<BR>Weight<BR>Descent<BR>Speed kias<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 59 -<BR>Note that the effect of the descent Mach number is very dependant on cruise<BR>flight level and descent speed, but is relatively small compared to the descent<BR>speed effect, and is not fully investigated here.<BR>These descent charts are typical of the other Airbus aircraft. Generally they<BR>show a minimum fuel speed of 260 to 280 kts for flight level 310, reducing to<BR>240kts for flight level 390. The exceptions are the A318, A319, A320 and A330,<BR>which show the minimum fuel at 240kias for all flight levels which is slightly lower<BR>than the other aircraft at FL310.<BR>Appendix B presents some examples of these descent charts for other Airbus<BR>aircraft.<BR>The following tables show, for various Airbus aircraft, the descent time and<BR>fuel variations for a fixed distance, from FL 350, relative to a 300kias reference<BR>speed.<BR>* A300/A310/A320 330kias A330/A340 340kias<BR>Type ΔFuel – kg<BR>240KT 260 KT 280 KT 300 KT 320 KT 330/340KT<BR>*<BR>A300 -55 -60 -30 0 25 35<BR>A310 -55 -60 -30 0 25 40<BR>A318, 319, 320 -50 -40 -20 0 20 25<BR>A321 -35 -40 -20 0 20 35<BR>A330 -110 -105 -60 0 50 70<BR>A340–200/300 -70 -90 -50 0 50 75<BR>A340-500/600 -125 -130 -70 0 70 100<BR>Type ΔTime – minutes<BR>240 KT 260 KT 280 KT 300 KT 320 KT 330/340KT<BR>*<BR>A300 2.7 1.5 0.6 0 -0.4 -0.6<BR>A310 2.4 1.4 0.6 0 -0.4 -0.6<BR>A320 family 2.6 1.4 0.6 0 -0.4 -0.6<BR>A330 3.5 2.0 0.8 0 -0.6 -0.8<BR>A340–200/300 3.2 1.8 0.8 0 -0.6 -0.8<BR>A340-500/600 3.3 1.9 0.8 0 -0.6 -0.8<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 60 -<BR>Comparing these tables to the equivalent climb comparison tables in<BR>chapter 5.2.4, it can be noticed that descent techniques often have a<BR>greater effect on fuel and time than climb techniques.<BR>5.4.3 MANAGED MODE DESCENT<BR>The FMS computes the Top Of Descent (TOD) as a function of the cost index.<BR>We notice that the higher the cost index:<BR>The steeper the descent path (the higher the speed)<BR>The shorter the descent distance<BR>The later the top of descent.<BR>Descent performance is a function of the cost index; the higher the cost<BR>index, the higher the descent speed. But contrary to climb, the aircraft gross<BR>weight and the top of descent flight level appear to have a negligible effect on the<BR>descent speed computation.<BR>It can be noticed that time to descent is more dependant on cost indices<BR>than the time to climb.<BR>On the Effect of Descent Technique on Fuel and Time chart, the cost index<BR>has been annotated for each speed. It can be seen that the minimum fuel is at a<BR>CI of 0, and the minimum time occurs with a high CI, as would be expected.<BR>For the A300, A310 and A320 family the speed at zero cost index is about<BR>250kias. For the A330/340 it is about 270kias. Max speed normally corresponds<BR>with a high cost index of 60 to 120. Once more it can be seen how, in the<BR>managed mode, the cost index is used to choose the balance between fuel burn<BR>and flight time.<BR>5.4.4 EARLY DESCENT<BR>If the aircraft begins its descent too early, the aircraft would leave its optimal<BR>flight level, where fuel consumption is at its best, and would have to cruise at a<BR>lower altitude to arrive at the same point.<BR>Cruise Flight Level<BR>•<BR>TOD<BR>Early Descent<BR>FL 100<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 61 -<BR>Two descent situations were simulated:<BR>• Descent commenced 15nm (or about 2 minutes) early followed by a leveloff<BR>at FL100.<BR>• Cruise continued from the early descent point until the optimum start of<BR>descent, followed by the descent<BR>At 10000ft, the cruise speed could be selected between LRC and max speed.<BR>If in managed mode, one could continue at the same cost index, or select the<BR>250kias below 10000ft limiting speed. The following table compares the two<BR>options.<BR>Aircraft 250KIAS at FL100 LRC at FL100<BR>ΔFuel – kg ΔTime – min ΔFuel – kg ΔTime – min<BR>A300-600 70 1.1 95 0.4<BR>A310 70 1.1 90 0.3<BR>A320 family 50 1.1 65 0.2<BR>A330 80 1.2 100 0.5<BR>A340-200/300 95 1.2 105 0.5<BR>A340-500/600 135 1.2 125 0.5<BR>Cruising faster at 10000ft reduces the time penalty at the expense of fuel.<BR>After a long flight with an A340–500 or –600, starting the descent some<BR>100nm early would not appear to be significant in the overall flight. However this<BR>can result in a 900kg fuel burn increase and 8 minutes longer block time.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 62 -<BR>5.5 HOLDING<BR>5.5.1 INTRODUCTION<BR>When holding is required, it is generally flown on a “race track pattern”,<BR>composed of two straight legs plus two 180 degree turns. In a hold the distance<BR>covered is not the primary objective. On the contrary, the knowledge of the<BR>maximum holding time (maximum endurance) is a determining factor for any<BR>diversion decision. As a result, it is important, during holding, to try to minimize<BR>fuel by simply minimizing fuel flow.<BR>For all aircraft, the minimum fuel consumption speed is very close<BR>to the maximum lift-to-drag ratio (Green Dot) speed as shown below. As a result,<BR>in clean configuration, the standard holding speed is selected equal to green dot<BR>speed (GD).<BR>Fuel Consumption<BR>A330-343 170000kg 1500ft<BR>0<BR>2000<BR>4000<BR>6000<BR>8000<BR>160 180 200 220 240 260 280 300 320<BR>Speed - Knots CAS<BR>Fuel Consumption kg/hr<BR>GD<BR>Min Fuel Min Drag Max Range Long Range<BR>Holding patterns may be quite limiting around certain airports due to<BR>obstacle proximity. Therefore, green dot is sometimes too high, especially during<BR>turn phases where the bank angle can be too significant. As it is not possible to<BR>significantly reduce the speed below green dot in clean configuration, slats may<BR>be extended and a holding done in CONF1 at “S” speed. (min slat retraction<BR>speed Conf 1 to Conf clean).<BR>At other airports, Air Traffic Control may require the hold to be performed at a<BR>certain speed, and it may not be possible fully optimise the fuel burn. In order to<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 63 -<BR>allow flexibility in planning and operations, the FCOM has four different holding<BR>speed and configuration combinations, adapted to each type of aircraft.<BR>The following table gives the configurations and speeds for each type.<BR>Aircraft types<BR>First Flap/slat<BR>Configuration Clean configuration<BR>A300-600 210kts S speed 240kts Green Dot<BR>A310 170kts S speed 210kts Green Dot<BR>A320 Family (CFM) 170kts S speed 210kts Green Dot<BR>A320 Family (IAE) 170kts S speed 210kts<BR>Green Dot +<BR>20<BR>A330 170kts S speed 210kts Green Dot<BR>A340-200/300 210kts S speed 240kts Green Dot<BR>A340-500/600 240kts S speed - Green Dot<BR>For the A300/A310 the first configuration is flap 15, slat 0. For the other<BR>aircraft this is Conf 1. Note that the fourth combination for the A340-500/600 is<BR>Configuration 2 at 210kts.<BR>5.5.2 VARIOUS CONFIGURATION / SPEED COMBINATIONS<BR>The following graphs show the holding fuel flow variation with weight for the<BR>four different holding configurations. This is done at an altitude of 10000ft.<BR>Effect of Holding Technique on Fuel Flow<BR>A300B4-605R ISA F/L 100<BR>2500<BR>3000<BR>3500<BR>4000<BR>4500<BR>5000<BR>90 95 100 105 110 115 120 125 130<BR>Aircraft Weight - tonnes Fuel Flow -<BR>kg/h<BR>Clean Green Dot<BR>Clean 240 kt<BR>15/0 'S' Speed<BR>15/0 210kt<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 64 -<BR>This graph is for an A300 and it shows the advantage of holding in a clean<BR>configuration at the green dot speed. The clean configuration fixed speed of 240kt<BR>is significantly higher than the green dot speed; hence the large increase in fuel<BR>flow with this technique. The 15/0 configuration with a fixed speed of 210kt is also<BR>significantly higher than the ‘S’ speed, hence higher fuel flows.<BR>The large variation in fuel flow shows how important it is to use the right<BR>configuration and speed, compatible with the other operational requirements.<BR>The A340-200/300 schedules the same hold speeds as the A300, and the<BR>graphs have a similar form with a large increase in fuel flow at low weights with<BR>the fixed speed techniques. However at high weights the difference is much<BR>smaller. There is also a large increase when using Conf 1. Once more holding<BR>clean at green dot speed gives the lowest fuel flow.<BR>The following graph is for the A310 and this shows completely different<BR>characteristics because of the lower fixed speeds used in each configuration.<BR>Each configuration shows very similar fuel flow, whichever speed technique is<BR>used. The clean configuration green dot speed still represents the best single<BR>choice for lowest fuel burn over the normal holding weight range.<BR>The A330, which has the same hold speed schedules shows the same<BR>characteristics, with clean configuration at green dot speed being marginally<BR>better than clean configuration at 210kt over the normal holding weight range.<BR>The A320 family shows a completely different set of characteristics as shown<BR>in the graph on the next page.<BR>Effect of Holding Technique on Fuel Flow<BR>A310-324 ISA F/L 100<BR>2500<BR>3000<BR>3500<BR>4000<BR>4500<BR>5000<BR>90 95 100 105 110 115 120 125 130<BR>Aircraft Weight - tonnes<BR>Fuel Flow - kg/h<BR>Clean Green Dot<BR>Clean 210kt<BR>15/0 'S' Speed<BR>15/0 170kt<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 65 -<BR>The variation of different techniques is very weight sensitive. However it is<BR>still the clean configuration at green dot speed that gives the lowest fuel flow. This<BR>picture is typical of all the A320 family.<BR>Finally the A340-500/600 has another set of configuration/speed<BR>combinations and the following graph shows its different characteristics, but the<BR>basic concept that the clean configuration and green dot is the best combination<BR>still remains true.<BR>Effect of Holding Technique on Fuel Flow<BR>A320-214 ISA F/L 100<BR>1400<BR>1600<BR>1800<BR>2000<BR>2200<BR>2400<BR>2600<BR>2800<BR>40 45 50 55 60 65 70<BR>Aircraft Weight - tonnes<BR>Fuel Flow - kg/h<BR>Clean Green Dot<BR>Clean 210kt<BR>Conf 1 'S' Speed<BR>Conf 1 170kt<BR>Effect of Holding Technique on Fuel Flow<BR>A340-642 ISA F/L 100<BR>5500<BR>6000<BR>6500<BR>7000<BR>7500<BR>8000<BR>8500<BR>9000<BR>9500<BR>10000<BR>200 220 240 260 280<BR>Aircraft Weight - tonnes<BR>Fuel Flow - kg/h<BR>Clean Green Dot<BR>Conf 1 240kt<BR>Conf 1 'S' Speed<BR>Conf 2 210kt<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 66 -<BR>There is also altitude to be considered, although it is often not the<BR>operator’s decision what flight level to hold at. Altitude has different effects on the<BR>fuel flow, depending on the airframe/engine combination. However, whatever the<BR>altitude effect, it generally affects all techniques equally; generally the higher the<BR>hold altitude the lower the fuel flow. This however is true only up to a certain<BR>altitude and this varies with each type.<BR>The following table shows this altitude effect for a hold in the clean<BR>configuration at green dot speed. The holding fuel flow is compared with the<BR>lowest for the flight levels considered for each type, and the difference expressed<BR>as a percentage.<BR>Flight Level 50 100 150 200 250 300 350 400<BR>A300B4-605R 4 2 1 0 3 8 16<BR>A310-324 11 5 2 0 0 5 9 23<BR>A318-111 13 8 4 2 1 0 0 5<BR>A319-112 19 11 3 1 0 1 0 4<BR>A320-214 13 5 3 1 1 1 0 2<BR>A320-232 7 5 5 5 2 0 4 11<BR>A321-211 14 11 8 3 0 1 5<BR>A330-203 2 1 0 0 2 4 8 18<BR>A330-223 9 9 5 2 0 1 6 14<BR>A340-343 10 5 1 0 0 2 7 16<BR>A340-212 3 2 0 0 2 3 5<BR>A340-313E 2 1 0 0 2 3 5<BR>A340-642 6 2 0 1 2 3 4 11<BR>In order to allow an assessment of the sensitivity of each aircraft type to<BR>different hold techniques, the following table shows the extra fuel required to<BR>hold for 15 minutes at 10000ft in the first flap configuration at ‘S’ speed,<BR>compared to Conf clean at green dot speed.<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 67 -<BR>Effect of Holding in First flap Setting at ‘S’ speed compared with Clean at Green Dot speed<BR>Aircraft types<BR>Fuel Increase (kg)<BR>Low Holding<BR>Weight<BR>Fuel Increase (kg)<BR>High Holding<BR>Weight<BR>A300B4-605R 70 110<BR>A300B4-622R 110 190<BR>A310-324 70 135<BR>A318 5 10<BR>A319 10 30<BR>A320 10 30<BR>A321 30 50<BR>A330-203 135 175<BR>A330-223 175 205<BR>A330-343 145 175<BR>A340-212 170 230<BR>A340-313 125 175<BR>A340-642 130 150<BR>The table shows that the green dot speed/clean configuration combination<BR>enables significant savings to be made.<BR>However, green dot speed increases with weight and can become higher<BR>than the maximum recommended speeds, which are listed below:<BR>Levels ICAO PAN-OPS FAA France<BR>Up to 6,000 ft inclusive 230 KT 210 KT 200 KT 220 KT<BR>Above 6,000 ft to 14,000 ft inclusive 230 KT 230 KT 230 KT 220 KT<BR>Above 14,000 ft to 20,000 ft inclusive 240 KT 240 KT 265 KT 240 KT<BR>Above 20,000 ft to 24,000 ft inclusive 265 KT 240 KT 265 KT 240 KT<BR>Above 24,000 ft to 34,000 ft inclusive 265 KT 240 KT 265 KT 265 KT<BR>Above 34,000 ft M 0.83 240 KT 265 KT M 0.83<BR>If green dot is higher than these maximum recommended speeds, it is<BR>advised to hold in configuration 1 at “S” speed below 20000ft: keeping clean<BR>configuration coupled with a speed reduction would save fuel but would decrease<BR>the speed margins which are especially important in turbulent conditions.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 68 -<BR>5.5.3 LINEAR HOLDING<BR>If holding is going to be necessary, linear holding at cruise flight level and at<BR>green dot speed should be performed whenever possible since total flight time will<BR>remain constant (cruise time is increased but holding time is reduced) and fuel<BR>flow is lower at high flight levels.<BR>If A.T.C. informs 15 minutes before reaching a fix and that 10 minutes<BR>holding is expected. Two options are possible:<BR>• The aircraft is flown 15 minutes at cruise speed and holds for 10 minutes at<BR>green dot speed.<BR>• The aircraft performs the cruise to reach the fix at green dot speed and<BR>holds for the remaining time at the same speed.<BR>10 minutes holding<BR>at green dot speed<BR>15 minutes at cruise<BR>d<BR>Holding at cruise<BR>Holding for remaining<BR>time at green dot speed<BR>Cruise at green dot speed<BR>Holding optimization<BR>Getting to grips with Fuel Economy IN FLIGHT PROCEDURES<BR>- 69 -<BR>ATC restrictions may not permit a cruise speed reduction at the cruise flight<BR>level, or permit a hold at the cruise flight level. The standard procedure would be<BR>to continue to the top of descent at cruise speed and descend to a flight level to<BR>join the stack. However if ATC permit a linear hold it can give significant fuel<BR>savings.<BR>However the amount of savings is very dependant on the characteristics of<BR>the aircraft type. The increase in time in the cruise depends on how much slower<BR>green dot speed is compared to the normal cruise speed. This increase was much<BR>higher with the A320 than the A340. In addition, most aircraft, flying the same<BR>cruise distance at green dot speed actually uses a little more fuel at these<BR>altitudes. The following table shows the gains due to cruising slower and<BR>spending less time in the hold at the cruise flight level.<BR>Advantages of a 15min linear hold at cruise altitude at Green Dot speed<BR>Aircraft type Weight kg<BR>Cruise<BR>Flight Level<BR>Cruise<BR>Speed<BR>Fuel<BR>savings kg<BR>A300 120000 350 0.8 95<BR>A310 110000 350 0.8 115<BR>A318 50000 350 0.78 120<BR>A319 50000 350 0.78 135<BR>A320 60000 350 0.78 80<BR>A321 70000 350 0.78 50<BR>A330 180000 390 0.82 95<BR>A340-200 200000 390 0.82 10<BR>A340-300 200000 390 0.82 45<BR>A340-500/600 270000 390 0.82 5<BR>The high green dot speed for the A340 leads to very little advantage in linear<BR>holding. However the other aircraft show significant benefits.<BR>If the increase in cruise time can be used to reducing the time in the holding<BR>pattern or stack, then the benefits will be similar to those shown in the table<BR>above. However the constraints of ATC are unlikely to let these benefits accrue.<BR>5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy<BR>- 70 -<BR>5.6 APPROACH<BR>5.6.1 FLIGHT PATH PRIOR TO GLIDE SLOPE INTERCEPTION<BR>Procedures used in the approach phase can affect the amount of fuel<BR>consumed in this phase of the flight. The glide slope can be intercepted either<BR>horizontally between 1500ft and 2000ft or in a descending flight path above<BR>2000ft. This latter method uses less fuel, but the amount is difficult to quantify, as<BR>it depends on the exact flight paths in each case. However, the most important<BR>feature of an approach is that it should be well executed, stabilized and safe.<BR>None of these features should be compromised in an attempt to save fuel, and the<BR>procedure flown should be that appropriate to the airport, runway, equipment,<BR>conditions, etc.<BR>5.6.2 LANDING GEAR EXTENSION<BR>The standard procedure is that Gear Down is selected down when Conf 2 (or<BR>flap 20 for A300/310) is achieved. The effect of extending the gear prior to this<BR>point will increase fuel burn, but the amount is difficult to quantify without<BR>knowing when the gear is extended. However, the most important feature of an<BR>approach is that it should be well executed, stabilized and safe. The use of gear is<BR>often one of the means of achieving this through speed control, and gear<BR>extension should not be delayed to save fuel.<BR>Getting to grips with Fuel Economy 6 - DETAILED SUMMARY<BR>- 71 -<BR>6. DETAILED SUMMARY<BR>6.1 INTRODUCTION<BR>In this brochure it can be seen that there are many ways of influencing the<BR>fuel burn of an aircraft, but most depend on the way that the sector is planned<BR>and flown. Maximising the fuel economy requires:<BR>• Good flight planning based on good data.<BR>• Correct aircraft loading (weight and cg).<BR>• An aerodynamically clean aircraft.<BR>• Optimal use of systems (APU, Bleed, Flaps/Slats, Gear, etc).<BR>• Flight Procedures using speeds and altitudes appropriate to the<BR>companies economic priorities.<BR>• Use of the FMGS in the managed mode.<BR>• Use of performance factors in flight planning and in the FMGS derived<BR>from an ongoing aircraft performance monitoring program.<BR>6.2 GENERAL GUIDELINES<BR>6.2.1 PRE-FLIGHT PROCEDURES<BR>• For most Airbus aircraft, an aft CG position saves fuel.<BR>• Excess weight costs fuel. Minimize zero fuel weight and embarked fuel.<BR>• A good flight planning system will minimise fuel through correct<BR>optimisation.<BR>• An aircraft performance measurement system and good flight planning<BR>will give confidence in fuel burn reducing extra reserve.<BR>• Keep A.P.U. running during short turnarounds to reduce A.P.U. start<BR>cycles.<BR>• Use ground power, when possible to save both fuel and A.P.U. life.<BR>7 – CONCLUSIONS Getting to grips with Fuel Economy<BR>- 72 -<BR>• Do not start engines until ready to go.<BR>• If considered operationally acceptable, taxi with one engine out.<BR>• Keep the aircraft in an aerodynamically clean condition.<BR>6.2.2 TAKE-FF AND INITIAL CLIMB<BR>• Bleeds off fuel improvements normally negated by APU fuel burn<BR>• Lower configurations do save fuel.<BR>• Flex thrust cost fuel but saves engine costs.<BR>• Noise flight paths cost fuel<BR>6.2.3 CLIMB<BR>• Climb as close as possible to the optimum climb law.<BR>• Fast Climb speeds use more fuel (except A340)<BR>6.2.4 CRUISE<BR>• The best speed for fuel burn (very low cost index) is slow and has a<BR>big time penalty.<BR>• If possible, fly in managed mode at the cost index appropriate to the<BR>airlines economic priorities.<BR>• Flying faster than the FMGS economical Mach number costs fuel.<BR>• Try to fly at optimum altitude. Chase the optimum altitude.<BR>• Flying at the cross-over altitude is faster, but costs fuel.<BR>• Step Climb around the optimum altitude (see FCOM).<BR>• Avoid delays in initiating a step climb.<BR>• For short stage lengths, fly at an appropriate altitude (see FCOM).<BR>• Wind variations with altitude can give advantages in flying at lower<BR>altitudes.<BR>6.2.5 DESCENT<BR>• Diminishing descent speed can allow significant fuel savings.<BR>• Avoid early descents<BR>Getting to grips with Fuel Economy 6 - DETAILED SUMMARY<BR>- 73 -<BR>6.2.6 HOLDING<BR>• The best combination for fuel burn is clean configuration at green dot<BR>speed.<BR>• Manoeuvrability, speed or ATC restrictions may require a hold in<BR>configuration 1 at S speed.<BR>• If holding is to be anticipated, linear holding saves fuel.<BR>6.2.7 APPROACH<BR>• Avoid extending gear unnecessarily early.<BR>6.3 FUEL SAVINGS<BR>The following table gives examples of the savings possible through the<BR>application of correct procedures and practices. The values represent typical<BR>saving as there is variation dependant on the actual base case considered.<BR>However these figures serve to illustrate the magnitude of savings being achieved<BR>(or penalties being paid). The savings are expressed in kg of fuel for one flight,<BR>with the sector length being representative for each aircraft.<BR>Fuel Savings Possible in the Pre-Flight phase<BR>Item Variation A300 A310 A320 A330 A340-<BR>200/300<BR>A340-<BR>500/600<BR>Sector 2000nm 2000nm 1000nm 4000nm 6000nm 6000nm<BR>CG mid to aft 710 330 0 600 900 1550<BR>Weight -1%<BR>MTOW<BR>380 250 100 800 1530 1920<BR>EO Taxi 8<BR>minutes<BR>50 40 25 50 50 70<BR>APU 3 min<BR>Grd<BR>Power<BR>9 9 6 10 10 14<BR>Ground<BR>Idle<BR>3 min<BR>APU<BR>18 18 9 15-24 3 9<BR>Misrigged<BR>Slat<BR>15mm to<BR>zero<BR>90 90 60 270 270 270<BR>Peeling<BR>Paint<BR>1sq m<BR>slat to<BR>zero<BR>12 12 8 60 60 60<BR>7 – CONCLUSIONS Getting to grips with Fuel Economy<BR>- 74 -<BR>Fuel Savings in the In Flight Phase<BR>Item Variation A300 A310 A320 A330 A340-<BR>200/300<BR>A340-<BR>500/600<BR>Sector 2000nm 2000nm 1000nm 4000nm 6000nm 6000nm<BR>TO Conf Max to min<BR>F/S<BR>15 15 10 24 - 50<BR>Climb<BR>Rating<BR>Derate 2<BR>to full<BR>Climb<BR>NA NA NA 30 120-320 445<BR>Climb<BR>Speed<BR>330 to<BR>300kias<BR>10 15 70 35 25 -10<BR>Cruise<BR>Altitude<BR>Optimum<BR>to –2000’<BR>65 80 80 100 95 135<BR>Cruise<BR>Altitude<BR>Optimum<BR>to +2000’<BR>90 60 25 145 30 25<BR>Cruise<BR>Mach<BR>Mecon+.01<BR>to Mecon<BR>230 430 40 330 900 2540<BR>Delayed<BR>Climb<BR>CFP to<BR>500nm<BR>late<BR>240 220 180 330 390 340<BR>CG mid to aft 710 330 0 600 900 1550<BR>Descent<BR>Speed<BR>Max to<BR>300kt<BR>35 40 30 70 75 100<BR>Early<BR>Descent<BR>CFP to<BR>2min early<BR>70 70 50 80 95 135<BR>Hold Green Dot<BR>Clean Conf<BR>190 135 30 205 230 130<BR>Getting to grips with Fuel Economy 6 - DETAILED SUMMARY<BR>- 75 -<BR>6.4 ECONOMIC BENEFITS<BR>It may be that 5 or 10 kg extra fuel per flight does not seem significant in<BR>terms of the total fuel burn during the flight. However this saving accumulates<BR>with every flight. Sometimes the savings for an A340 seem worthwhile compared<BR>with the equivalent value for an A320, but the increased number of flight cycles<BR>for an A320 can make this saving more significant than that of the A340. The only<BR>way to assess the impact of any saving is to look at it over a given time span.<BR>The economic impact calculations have assumed typical yearly utilisation<BR>rates, average sector lengths and sectors per year as follows:<BR>The following table shows the annual cost savings for one aircraft associated<BR>with various fuel savings for each Airbus type based on the above utilisation<BR>figures. Fuel is assumed to cost $1/us gallon (33cents/kg).<BR>Utilisation A300 A310 A320 A330 A340<BR>Flying<BR>Hours/year<BR>2600 3200 2700 2900 4700<BR>Average<BR>sector - nm<BR>2000 2000 1000 4000 6000<BR>Average flight<BR>time - hr<BR>4.5 4.6 2.4 8.5 13.8<BR>No of<BR>sectors/year<BR>580 700 1125 340 340<BR>Savings/flight A300 A310 A320 A330 A340<BR>10kg $1920 $2310 $3720 $1120 $1120<BR>50kg $9600 $11550 $18600 $5600 $5600<BR>250kg $48000 $57750 $93000 $28000 $28000<BR>1000kg $192000 $231000 $372000 $112000 $112000<BR>7 – CONCLUSIONS Getting to grips with Fuel Economy<BR>- 76 -<BR>7. CONCLUSIONS<BR>There are many factors that influence the fuel used by aircraft, and these are<BR>highlighted in this report. The unpredictability of fuel prices, together with the fact<BR>that they represent such a large burden to the airline has prompted Airbus to be<BR>innovative in the field of fuel conservation. The relationship between fuel used and<BR>flight time is such that sometimes compromise is necessary to get the best<BR>economics. Whether in the field of design engineering or in flight operations<BR>support, we have always maintained a competitive edge. Whether it is in short or<BR>ample supply, we have always considered fuel conservation a subject worth<BR>revisiting.<BR>Fuel conservation affects many areas including flight planning, flight<BR>operations and maintenance. Airbus is willing and able to support airlines with<BR>operational support in all the appropriate disciplines. Despite the increasing<BR>efficiency of modern aircraft it is a subject that demands continuous attention and<BR>an airline that can focus on the subject, together with the Operation Support of<BR>Airbus is best placed to meet the challenges of surviving and profiting in the harsh<BR>airline environment of the 21st century.<BR>Getting to grips with Fuel Economy 8 - APPENDIXES<BR>- 77 -<BR>8. APPENDICES<BR>These appendices contain climb and descent graphs for some of the other<BR>variants of Airbus aircraft. Each airframe/engine combination have different<BR>characteristics. Even the weight variant can influence these characteristics. It is<BR>therefore impossible to include all variants, but the selection shown will give an<BR>idea of the sensitivities of fuel burn and time to technique.<BR>8 - APPENDICES Getting to grips with Fuel Economy<BR>- 78 -<BR>APPENDIX A (CLIMB CHARTS)<BR>The climb chart for the A300 is given in the main report (5.2.3)<BR>The A310 shows similar characteristics and is shown below. Note that the<BR>lower mach numbers (0.76, 0.78 and 0.8) show no variation.<BR>The main report gives the climb chart for the A320 which is similar to the<BR>A318 and A319. The A321 however shows more significant differences.<BR>Effect of Climb Technique on fuel and time to 130nm<BR>A310-324 ISA F/L 350 Weight 130000kg<BR>-6.00%<BR>-4.00%<BR>-2.00%<BR>0.00%<BR>2.00%<BR>4.00%<BR>6.00%<BR>-1.00% 0.00% 1.00% 2.00% 3.00% 4.00%<BR>Fuel - %<BR>Time %<BR>FMGS<BR>280<BR>300<BR>320<BR>330<BR>Climb Speed kias<BR>270<BR>100kg<BR>1 minute<BR>M 0.82<BR>Effect of Climb Technique on fuel and time to 230nm<BR>A321-211 ISA F/L 350 Weight 80000kg<BR>-6.00%<BR>-4.00%<BR>-2.00%<BR>0.00%<BR>2.00%<BR>4.00%<BR>6.00%<BR>-2.00% -1.00% 0.00% 1.00% 2.00% 3.00% 4.00% 5.00% 6.00%<BR>Fuel %<BR>Time %<BR>M No<BR>FMGS<BR>0.76<BR>0.8<BR>100 kg<BR>1 minute<BR>0<BR>100<BR>Getting to grips with Fuel Economy 8 - APPENDIXES<BR>- 79 -<BR>The A330 aircraft show characteristics similar to the A321 and an example<BR>is shown below.<BR>The A340-200/300 series show characteristics approaching that of the<BR>A340-500/600 but still shows minimum fuel at a speed lower than max, unlike the<BR>A340-500/600 (see 5.2.3).<BR>Effect of Climb Technique on fuel and time to 220nm<BR>A340-313E ISA F/L 350 Weight 240000kg<BR>-6.00%<BR>-4.00%<BR>-2.00%<BR>0.00%<BR>2.00%<BR>4.00%<BR>6.00%<BR>-1.00% 0.00% 1.00% 2.00% 3.00%<BR>Fuel %<BR>Time %<BR>M No<BR>FMGS<BR>0.76<BR>0.78<BR>0.8<BR>280<BR>300<BR>320<BR>340<BR>Climb Speed kias<BR>0.82<BR>270<BR>100kg<BR>1 minute<BR>Effect of Climb Technique on fuel and time to 150nm<BR>A330-343 ISA F/L 350 Weight 190000kg<BR>-6.00%<BR>-4.00%<BR>-2.00%<BR>0.00%<BR>2.00%<BR>4.00%<BR>6.00%<BR>-1.00% 0.00% 1.00% 2.00% 3.00%<BR>Fuel %<BR>Time %<BR>M No<BR>FMGS<BR>0.8 0.76<BR>280<BR>300<BR>320<BR>340<BR>Climb Speed kias<BR>0.82<BR>270<BR>100 kg<BR>1 minute<BR>0<BR>100<BR>8 - APPENDICES Getting to grips with Fuel Economy<BR>- 80 -<BR>APPENDIX B (DESCENT CHARTS)<BR>The A300 shows similar characteristics to the A310 in the main report.<BR>The A320 shown below has similar characteristics to the A318, A319 and<BR>A321.<BR>Effect of Descent Technique on Fuel and Time for 115nm<BR>A300B4-605R ISA Weight 120000kg<BR>17.5<BR>18.0<BR>18.5<BR>19.0<BR>19.5<BR>20.0<BR>20.5<BR>21.0<BR>21.5<BR>22.0<BR>250 300 350 400 450 500 550 600<BR>Fuel - kg<BR>Time - min<BR>240<BR>250<BR>260<BR>300<BR>320<BR>330<BR>6<BR>28<BR>50<BR>72<BR>100<BR>390 370 350 330 310<BR>Initial Flight Level<BR>Cost<BR>Index<BR>Descent<BR>Speed KIAS<BR>Effect of Descent Technique on Fuel and Time for 120nm<BR>A320-214 ISA Weight 60000kg<BR>16.0<BR>17.0<BR>18.0<BR>19.0<BR>20.0<BR>21.0<BR>22.0<BR>23.0<BR>200 250 300 350 400 450<BR>Fuel - kg<BR>Time - min<BR>240<BR>250<BR>260<BR>300 320<BR>340<BR>0<BR>24<BR>36<BR>50<BR>80<BR>390 370 350 330 310<BR>Initial Flight<BR>Cost<BR>Index<BR>Descent<BR>Speed KIAS<BR>280<BR>9<BR>Getting to grips with Fuel Economy 8 - APPENDIXES<BR>- 81 -<BR>The following shows an example of an A330:<BR>Most of the A340’s have similar speed characteristics to the A340-642<BR>shown below. The A340-200 does however show an improvement in fuel for<BR>speeds lower than 260kts.<BR>Effect of Descent Technique on Fuel and Time for 160nm<BR>A330-343 ISA Weight 180000kg<BR>24.0<BR>25.0<BR>26.0<BR>27.0<BR>28.0<BR>29.0<BR>30.0<BR>500 600 700 800 900 1000 1100<BR>Fuel - kg<BR>Time - min<BR>240<BR>250<BR>260<BR>300<BR>320<BR>340<BR>48<BR>310<BR>390 370 I3n5i0tial Flight Le3v3e0l<BR>Cost<BR>Index<BR>Descent<BR>Speed<BR>KIAS<BR>280<BR>30<BR>CI=0 270kias<BR>CI=60 315kias<BR>CI=100 315kias<BR>Effect of Descent Technique on Fuel and Time for 160nm<BR>A340-642 ISA Weight 270000kg<BR>24.0<BR>25.0<BR>26.0<BR>27.0<BR>28.0<BR>29.0<BR>30.0<BR>700 800 900 1000 1100 1200 1300 1400 1500 1600<BR>Fuel - kg<BR>Time - min<BR>240<BR>250<BR>260<BR>300<BR>320<BR>340<BR>78<BR>310<BR>370 350 330<BR>390<BR>Initial Flight Level<BR>Cost<BR>Index<BR>Descent Speed<BR>KIAS<BR>280<BR>21<BR>CI=0 272kias<BR>CI=100 308kias

sunenjoy 发表于 2010-8-25 21:38:19

<P>能看看吗?</P>

xheleon 发表于 2010-8-28 17:24:12

非常感谢楼主发布!!!!

bocome 发表于 2011-4-5 22:36:37

study hard

leoyuxin 发表于 2011-4-8 20:31:41

回复 1# 航空 的帖子

好的,谢谢楼主的分享。

kinran 发表于 2011-4-8 21:14:28

留下了~~~~~~~~

kinran 发表于 2011-4-8 21:14:46

留下了~~~~~~~~
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