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Fuel Conservation
Flight Operations Engineering
Boeing Commercial Airplanes
November 2004
Fuel Conservation 2
What is Fuel Conservation?
Fuel conservation means managing the
operation and condition of an airplane to
minimize the fuel used on every flight
Fuel Conservation 3
*Assumes typical airplane utilization rates. Actual utilization rates may differ.
How Much Is A 1% Reduction In Fuel Worth?
Airplane Fuel savings*
type gal/year/airplane
777 70,000 → 90,000
767 30,000 → 40,000
757 25,000 → 35,000
747 100,000 → 135,000
737 15,000 → 25,000
727 30,000 → 40,000
Fuel Conservation 4
How Much Is This Worth In $$?
Depends on Current Fuel Prices!
Fuel Conservation 5
Jet Fuel Prices
Source: Air Transport World
Year
$/gallon
$0.00
$0.20
$0.40
$0.60
$0.80
$1.00
$1.20
$1.40
87 89 91 93 95 97 99 01 03
$1.00
Fuel Conservation 6
Airplane Fuel savings* Fuel savings*
type gal/year/airplane $/year/airplane
*Assumes $1.00/gallon
How Much Is A 1% Reduction In Fuel Worth?
777 70,000 → 90,000 $70,000 → 90,000
767 30,000 → 40,000 $30,000 → 40,000
757 25,000 → 35,000 $25,000 → 35,000
747 100,000 → 135,000 $100,000 → 135,000
737 15,000 → 25,000 $15,000 → 25,000
727 30,000 → 40,000 $30,000 → 40,000
*Assumes typical airplane utilization rates. Actual utilization rates may differ.
Fuel Conservation 7
What Is Fuel Conservation
From An Airline Business Viewpoint ?
Fuel conservation means managing the
operation and condition of an airplane to
minimize the fuel used on every flight
total cost of
Fuel Conservation 8
Total savings =
fuel savings
- cost to
implement
Cost to Total Cost
Implement Savings/AP
?? ??
Airplane Fuel savings* Fuel savings*
type gal/year/airplane $/year/airplane
How Much Is A 1% Reduction In Fuel Worth?
777 70,000 → 90,000 $70,000 → 90,000
767 30,000 → 40,000 $30,000 → 40,000
757 25,000 → 35,000 $25,000 → 35,000
747 100,000 → 135,000 $100,000 → 135,000
737 15,000 → 25,000 $15,000 → 25,000
727 30,000 → 40,000 $30,000 → 40,000
*Assumes $1.00/gallon
*Assumes typical airplane utilization rates. Actual utilization rates may differ.
Fuel Conservation 9
Saving Fuel Requires Everyone’s Help
• Flight Operations
• Dispatchers
• Flight Crews
• Maintenance
• Management
10
FLIGHT
OPERATIONS
ENGINEERING
Operational Practices
for Fuel Conservation
Fuel Conservation 11
Flight Operations / Dispatchers
• Landing weight
• Fuel reserves
• Airplane loading
• Flap selection
• Altitude selection
• Speed selection
• Route selection
• Fuel tankering
Opportunities For Fuel Conservation
Fuel Conservation 12
Reduced Landing Weight
1% reduction in landing weight produces:
≅ 0.75% reduction in trip fuel (high BPR engines)
≅ 1% reduction in trip fuel (low BPR engines)
Fuel Conservation 13
Required Additional
WLDG = OEW + Payload + reserve + fuel loaded
fuel but not used
Zero fuel weight
Fuel on board at landing
Components Of Landing Weight
Fuel Conservation 14
Approximate % Block Fuel Savings Per
1000 Lb (454 Kg) ZFW Reduction
737-
3/4/500
737-
6/7/8/900
757-
200/300
767-
2/3/400
777-
200/300 747-400
.7% .6% .5% .3% .2% .2%
717-200
.9%
Reducing ZFW Reduces Landing Weight
Fuel Conservation 15
Reducing OEW Reduces Landing Weight
• Passenger service items
• Passenger entertainment items
• Empty Cargo and baggage containers
• Unneeded Emergency equipment
• Excess Potable water
Items To Consider
Fuel Conservation 16
Reducing Unnecessary Fuel
Reduces Landing Weight
• Practice cruise performance monitoring
• Flight plan by tail numbers
Fuel Conservation 17
Fuel Reserves
• Carry the appropriate amount of reserves to ensure
a safe flight and to meet your regulatory requirements
• Extra reserves are extra weight
• Airplane burns extra fuel to carry the extra weight
Fuel Conservation 18
Fuel Reserves
The amount of required fuel reserves depends on:
• Regulatory requirements
• Choice of alternate airport
• Use of re-dispatch
• Company policies on reserves
• Discretionary fuel
Fuel Conservation 19
Regulatory Requirements
• Is this an international flight?
• FAA rules?
• ICAO rules?
• Other rules?
Fuel Conservation 20
FAA “International Reserves”
(A) To fly to and land at the airport to which it is released;
(B) After that, to fly for a period of 10 percent of the total time required to fly from the
airport of departure to, and land at, the airport to which it was released;
(C) After that, to fly to and land at the most distant alternate airport specified in the
flight release, if an alternate is required; and
(D) After that, to fly for 30 minutes at holding speed at 1,500 feet above the alternate
airport (or the destination airport if no alternate is required) under standard
temperature conditions.
FAR 121.645(b)
D
C
B
A
Conttiingency
Alltterrnatte
Holldiing
Fuel Conservation 21
FAA “Island Reserves”
• No alternate is specified in release under Section
121.621(a)(2) or Section 121.623(b).
• Must have enough fuel, considering wind and other
weather conditions expected, to fly to destination
airport and thereafter to fly for 2 hours at normal
cruising fuel consumption
FAR 121.645(c)
Fuel Conservation 22
ICAO International
4.3.6.3.1 When an alternate aerodrome is required;
To fly to and execute an approach, and a missed approach,
at the aerodrome to which the flight is planned, and
thereafter:
A) To fly to the alternate aerodrome specified in the
flight plan; and then
B) To fly for 30 minutes at holding speed at 450 M
(1,500 ft) above the alternate aerodrome under standard
temperature conditions, and approach and land; and
C) To have an additional amount of fuel sufficient to
provide for the increased consumption on the occurrence
of any of the potential contingencies specified by the
operator to the satisfaction of the state of the operator
(typically a percentage of the trip fuel: 3% to 6%).
C
A
B
Conttiingeenccyy
Holldiing
Alltteerrnaattee
ICAO Annex 6 (4.3.6.3)
Fuel Conservation 23
Alternate Airport
What items should you consider when choosing
an alternate airport?
• Airline facilities
• Size and surface of runway
• Weather
• Hours of operation, lighting
• Fire fighting, rescue equipment
Fuel Conservation 24
Alternate Airport
What items should you consider when choosing
an alternate airport?
• Airline facilities
• Size and surface of runway
• Weather
• Hours of operation, lighting
• Fire fighting, rescue equipment
Fuel Conservation 25
Speed Selection for Holding
• Want to maximize time per kilogram of fuel
• Use published/FMC recommended holding
speeds
Fuel Conservation 26
Use Redispatch to Lower Contingency Fuel
• Reserve/contingency fuel is a function of trip
length or trip fuel burn
• Originally implemented to cover errors in
navigation, weather prediction, etc...
• Navigation and weather forecasting techniques
have improved, decreasing the chance that
contingency fuel will actually be used
Fuel Conservation 27
How Redispatch Works
Climb
Descent
Cruise
Intended
destination
Origin
Redispatch
point
Initial
destination
Fuel Conservation 28
Intended
Origin destination
Intended
Origin destination
Redispatch
point
Initial
destination
Redispatch
point
Initial
destination
Off Track Initial Destination
Fuel Conservation 29
Intent is to lower the Contingency Fuel On
Board at the Final Destination
Distance
(Time)
Redispatch
point
Contingency
fuel
Contingency Fuel required
Intended
destination
Contingency
Fuel required
Reduction
Fuel Conservation 30
Reduced fuel load
Increased payload
Benefits of Redispatch
Fuel Conservation 31
B
Initial
destination
A
Origin
C
Final
destination
Examples of Using Redispatch
To: 1) Increase payload
2) Decrease takeoff and landing weight
(by reducing fuel load)
Fuel Conservation 32
Example of payload
increase with constant
takeoff weight
OEW
PAYLOAD
(1)
Altern + Hold
Contingency
TRIP
FUEL
TRIP
FUEL
Same takeoff weight with and
without redispatch
Optimum
redispatch point
A C
OEW
A B
(No redispatch)
PAYLOAD
(2)
Altern + Hold
Contingency
PAYLOAD
(2)
B C
OEW
TRIP FUEL
Altern + Hold
Contingency
Gross
weight
Fuel Conservation 33
Example of takeoff
weight and landing
weight decreases with
constant payload
OEW
PAYLOAD
(1)
Altern + Hold
Contingency
TRIP
FUEL
TRIP
FUEL
Optimum
redispatch point
A C
(No redispatch)
A B B C
OEW
PAYLOAD
(2)
PAYLOAD
(2)
OEW
TRIP FUEL
Altern + Hold
Contingency Contingency
Altern + Hold
Takeoff weight decrease
Landing
weight (1)
Landing weight (2)
(decrease from (1))
Gross
weight
Fuel Conservation 34
WT (fwd c.g.) Lift tail (fwd c.g.)
Lift wing (fwd c.g.)
• At aft c.g. the lift of the tail is less negative than at forward
c.g. due to the smaller moment arm between Liftwing and WT
• Less angle of attack, α, is required to create the lower Liftwing
required to offset the WT plus the less negative Lifttail
• Same Lifttotal, but lower Liftwing and therefore lower α required
Lift wing (aft c.g.)
WT (aft c.g.)
Lift tail (aft c.g.)
<
= Is less negative than
Airplane Loading
Maintain C.G. In The Mid To Aft Range
Fuel Conservation 35
4 8 12 16 20 24 28 32 36
Center of gravity, %MAC
Incremental
cruise drag, %
-2
-1
0
1
2
3
4
5
0.70
0.65
0.60
0.55
0.50
Typical trim drag increment at cruise Mach
Airplane Loading (continued)
Maintain C.G. in the Mid to Aft Range
W/δ (LB *10-6)
Actual variation in
drag due to C.G.
depends on airplane
design, weight,
altitude and Mach
Fuel Conservation 36
Flap Setting
Choose lowest flap setting that will meet takeoff
performance requirements:
• Less drag
• Better climb performance
• Spend less time at low altitudes, burn less fuel
Fuel Conservation 37
Altitude Selection
Pressure altitude for a given weight and speed
schedule that produces the maximum air miles per
unit of fuel
Optimum Altitude Definition
Fuel Conservation 38
Definition of Optimum Altitude
FUEL MILEAGE (NAM/LB)
PRESSURE ALTITUDE (1000 FT)
0.024 0.028 0.032 0.036 0.040 0.044 0.048
30
32
34
36
38
40
GROSS WT
(1000 LB)
620
580
540
500
460 420 380 340
300
OPTIMUM
(CONSTANT MACH
NUMBER)
Pressure Altitude Which Provides the Maximum Fuel
Mileage for a Given Weight and Speed
Fuel Conservation 39
LRC Mach
Determining Optimum Altitude
Cruise weight (1000 KG)
Brake release weight (1000 KG)
45
40
35
30
60 70 80 90 100 110 120
70 80 90 100 100 120
Pressure
altitude
(1000 ft)
Fuel Conservation 40
Step Climb
= Off optimum operations
Optimum
Altitude
4000 ft
2000 ft
Step
climb
Fuel Conservation 41
Optimum altitude
+ 1.5%
+ 1.5%
1000 ft
+ 0.5%
+ 3.0%
+ 0.5%
+ 6.5%
+ 1.5%
+ 8.5%
4-hour Average = + 4.8%
+ 0%
+ 4.5%
4-hour Average = + 0.6%
Off-Optimum Fuel Burn Penalty
4000 ft Step vs. No Step Over a 4-Hour Cruise
(Example Only)
Fuel Conservation 42
Speed Selection
NAM/
pound
fuel
MACH number
0.12
0.11
0.10
0.09
0.08
0.07
0.06
0.60 0.64 0.68 0.72 0.76 0.80 0.84
0.05
Increasing
weight
LRC
MMO
MRC = Maximum range cruise (speed producing maximum fuel mileage for a given weight)
LRC = Long Range cruise (speed which produces a 1% decrease in FM relative to MRC)
1%
LRC Versus MRC
MRC
Fuel Conservation 43
Speed Selection (continued)
• LRC = MRC + 1% fuel burn
• Significant speed increase for only
a 1% decrease in fuel mileage
• Increases speed stability
• Minimizes throttle adjustments
LRC Versus MRC
Fuel Conservation 44
0
1
2
3
4
5
6
7
8
0.00 0.01 0.02 0.03 0.04
Δ Mach from MRC
Δ Fuel ~ %
-30
-25
-20
-15
-10
-5
0
0.00 0.01 0.02 0.03 0.04
Δ Mach from MRC
Δ Time ~ min.
LRC
Model #1
Model #2
Model #2
Model #1
LRC Model #1
LRC Model #2
Δ Fuel For Flying Faster Than MRC
Flying Faster Than MRC?
Flying faster than LRC typically produces a significant fuel
burn increase in return for a relatively small time savings
(example based on 5000 NM cruise)
Δ Time For Flying Faster Than MRC
Actual fuel burn increase, and time decrease, for flying faster than
MRC depends on specific airplane model, weight, and altitude
Fuel Conservation 45
Speed Selection - Other Options
• Cost Index = 0 (maximize ngm/lb
= wind-adjusted MRC)
• Selected Cost Index (minimize costs)
• Maximum Endurance (maximize time/lb)
CI = Time cost ~ $/hr
Fuel cost ~ cents/lb
Fuel Conservation 46
Route Selection
Choose the most favorable route available!
Fuel Conservation 47
Great Circle Distance
• Shortest ground distance between 2 points on the
earth’s surface
• May not be the shortest time when winds are
included
Fuel Conservation 48
ETOPS
• ETOPS allows for more direct routes
• Shorter routes = less fuel required
New York
Montreal
St. Johns
Goose Bay
Iqaluit
Kangerlussuaq
Reykjavik
Shannon Paris
120 min
60 min
3148
3461
Using 120 min ETOPS leads to
a 9% savings in trip distance!
Fuel Conservation 49
Fuel Tankering
Fuel tankering is the practice of carrying
more fuel than required for a particular
sector in order to reduce the quantity of
fuel loaded at the destination airport for
the following sector (or sectors)
What Is It?
Fuel Conservation 50
A B C
Leg 1 Leg 2
Reserves
Fuel
for
leg 2
Fuel
for
leg 1
Fuel loaded at
A for leg 1
Fuel loaded at
B for leg 2
No tankering
of 2nd leg fuel
Reserves
Extra fuel burned
on leg 1 to carry
fuel for leg 2 Fuel
for
leg 2
Fuel
for
leg 1
100% tankering
of 2nd leg fuel
Fuel loaded
at A for legs 1 & 2
Fuel Tankering (continued)
Fuel Conservation 51
Reduction in total fuel costs for multiple leg
flights is usually the main reason for tankering
Fuel Tankering (continued)
• Shorter turnaround time
• Limited amount of fuel available
• Unreliable airport services
• Fuel quality at destination airport
• Fuel price differential
Why Tanker Fuel?
Fuel Conservation 52
Fuel Tankering (continued)
• If price at departure airport is sufficiently less than at the
destination airport, surplus fuel could be carried from
the departure airport to lower the total fuel cost
• Fuel used increases on flights where fuel is tankered
such that the quantity of fuel available at landing is
always less than what was originally loaded (often
called ‘surplus fuel burn-off’)
• Surplus fuel burn-off must be accounted for in any price
differential calculation
• To be cost-effective, the difference in fuel price between
the departure and destination airports must be large
enough to offset the cost of the additional fuel burned
in carrying the tankered fuel
Fuel Price Differential
Fuel Conservation 53
Fuel Tankering (continued)
• The amount of tankered fuel loaded may
be limited by:
– Certified MTOW
– Performance-limited MTOW
– Certified MLW
– Performance-limited MLW
– Fuel capacity
• These limits must always be checked when
loading extra fuel for tankering!
Limitations On Total Amounts
Fuel Conservation 54
Difficult to quantify, but should be
addressed in all cost calculations
Fuel Tankering (continued)
• Lowers initial cruise altitude capability
• Increases takeoff weight: higher takeoff speeds,
less reduced thrust, may require improved climb
• If landing is planned at or near MLW, and additional
fuel burn-off was over-predicted, an overweight
landing could result
• Higher maintenance costs: engines, reversers,
wheels, tires, brakes
Additional Considerations
Fuel Conservation 55
To Tanker or Not to Tanker
• Cost calculations vary between operators, ranging
from the fairly simple to the fairly complex
• Complexity of the calculations depends on the
requirements of your operations. (e.g., If the
decision to tanker is made by the captain at the
time of fueling, a simple method is desired)
• Many operators add a price per gallon, or a fixed
percentage, to cover increased maintenance costs
Cost Calculations
Fuel Conservation 56
Cost Calculations
We will briefly review 3 possible methods:
1) Assumed percentage burn-off
2) Break-even price ratio
3) Relative cost to tanker
Fuel Conservation 57
Cost Calculations (continued)
• All methods should begin by checking whether
takeoff and landing weight limits, along with fuel
capacity limits, allow additional fuel to be loaded
• Some operators choose a minimum tankering
amount such that if the amount available to tanker
is not at least equal to their chosen minimum,
no fuel will be tankered
Fuel Conservation 58
Cost Calculations (continued)
Calculation of fuel prices is not always as easy
as it first appears. Understand how fuel prices are
determined at your airline.
For example:
• Price may vary with amount purchased
• Fixed hookup fees should be included (affects
price per gallon - as more fuel is purchased,
the hookup price/gallon decreases)
• Taxes charged may be returned later as tax
rebates lower the price per gallon
Fuel Conservation 59
‘Assumed Percentage Burn-off’ Method
• Assumes a fixed percentage of the tankered fuel
is consumed per hour of flight time; usually 4 to 5%
per hour
• Divide total cost of additional fuel purchased
at departure airport by amount remaining at
destination airport to determine ‘effective’ price
of fuel at destination
• Assume some per gallon cost to cover unknowns
• Break-even price is the ‘effective’ price plus the
allowance for unknown costs
• If price of fuel at destination is above the breakeven
price, then it is cost-effective to tanker
Fuel Conservation 60
Example Cost Calculation
• Planned flight time = 6 hours
• Departure fuel price = $1.00/gallon
• Tankered fuel loaded = 40000 lb (6000 gallons)
• Cost of tankered fuel = $6000
• Surplus fuel burn-off (4%/hour) = 24%
• Tankered fuel at landing = 6000 x .76 = 4560 gallons
• Effective cost of tankered fuel = 6000/4560 = $1.32/gal
• Allowance for unknown cost = $.02/gal (typical?)
• Actual cost of tankered fuel = $1.32 + $.02 = $1.34/gal
• Cost-effective if destination fuel price above $1.34/gal
Fuel Conservation 61
Trip distance (nm) Break-even price ratio
200
400
600
800
1000
2000
3000
4000
5000
6000
1.012
1.023
1.034
1.046
1.061
1.130
1.217
1.334
1.495
1.722
Sample data only
varies with airplane model
• To economically justify tanker operation, the fuel
price at the destination must be greater than the
break-even fuel price
Break-Even Price Ratio Method
• Method used in Boeing FPPM (found in chapter 2 text)
• Break-even price ratio is presented as a function of trip
distance only
Fuel Conservation 62
$ * (tankered fuel) = $ * (tankered fuel - fuel burnoff)
gal gal Orig Dest = tankered fuel
remaining at dest
Break-even
Orig price ratio
$
gal Dest
B.E.
$
Break-even price = = gal *
at destination
Break-Even Price Ratio Method (continued)
• Break-even fuel price is the destination price at which the
cost of purchasing the fuel at the destination is equivalent
to the cost of purchasing the same amount of fuel, plus
the fuel required to carry it, at the origin
• Break-even price occurs when:
Fuel Conservation 63
Break-Even Price Ratio Method (continued)
• If the destination fuel price is greater than the breakeven
price, then it’s cheaper to tanker the fuel
• The break-even price ratio does not include any
allowance for additional maintenance costs; it only
considers the extra fuel burn off
Fuel Conservation 64
Example Cost Calculation
Fuel price at origin: $0.80/gal
Model: 737-700/CFM56-7B24
Trip distance: 2000 NM
Trip distance, nm Break-even price ratio
200
400
600
800
1000
2000
3000
4000
1.015
1.031
1.045
1.059
1.075
1.175
1.311
1.477
Break-even price = $0.80 ( 1.175) = $0.94
If dest. fuel price > $0.94, then more economical to tanker the fuel
If dest. fuel price < $0.94, then more economical to purchase at dest.
To include increased maintenance costs, should increase the B.E.
fuel price by the estimate (e.g., if unknown costs estimated at
$0.02/gal, then B.E. fuel price = $0.94 + $0.02 = $0.96)
Fuel Conservation 65
‘Relative Cost to Tanker’ Method
• Considers the difference in total cost between
tankering and not tankering the fuel
• Only includes costs related to tankering or not
tankering fuel
• Requires calculation of fuel required for actual
routes with and without tankering
Fuel Conservation 66
A B C
Leg 1 Leg 2
gal
A
$ Fuel
req’d
leg 1
Fuel
carried
for use
in leg 2
+
Extra fuel
burned on
leg 1 due to
extra wt
+ +
Additional
incremental
costs due to
higher weight gal
B
$
+
Additional
fuel req’d
for leg 2
*
total cost with tankering
-
gal
B
Fuel $
req’d
leg 1
-
gal
A
$ Fuel
req’d
leg 2
* *
Total cost with no tankering
‘Relative Cost to Tanker’ Method (continued)
Fuel Conservation 67
cost of tankering the fuel cost of purchasing
at the destination
gal
B
fuel $
carried
for use
in leg 2
+
extra fuel
burned on
leg 1 due to
extra weight
+
additional
incremental
costs due to
higher weight
- * gal
A
$
fuel
carried
for use
in leg 2
‘Relative Cost to Tanker’ Method (continued)
Relative cost to tanker =
Fuel Conservation 68
• If relative cost to tanker = 0, then breakeven
• If relative cost to tanker > 0, then costs are increased
by tankering
• If relative cost to tanker < 0, then costs are reduced
by tankering
• Some operators choose a minimum financial gain below
which there will not be tankering. (e.g., if minimum gain
selected as $100, then tankering will only be used if
relative cost to tanker < - $100)
• Multiple legs (3 or more) add significantly to the complexity
of the analysis
‘Relative Cost to Tanker’ Method (continued)
Fuel Conservation 69
Additional Applications
• If fuel is tankered in order to obtain a shorter turnaround
time at a given destination you can determine the
relative cost of the shorter turnaround time
• Cost to tanker can be used to provide flight crews
with information on the cost of carrying additional,
discretionary fuel
‘Relative Cost to Tanker’ Method (continued)
Fuel Conservation 70
Fuel Tankering
• Most flight planning services offer tankering
analyses to their customers
• You can work with your flight planning service on
which assumptions to use/include, and in what form
the results should be reported
Fuel Conservation 71
Flight Crew
Opportunities for Fuel Conservation:
• Practice fuel economy in each phase of flight
• Understand the airplane’s systems - Systems
Management
Fuel Conservation 72
Engine Start
• Start engines as late as possible, coordinate
with ATC departure schedule
• Take delays at the gate if possible
• Minimize APU use if ground power available
Fuel Conservation 73
Taxi
• Take shortest route possible
• Use minimum thrust and minimum braking
• Taxi with all engines operating?
Fuel Conservation 74
Taxi
• After-start and before-takeoff checklists delayed
• Reduced fire protection from ground personnel
• High weights, soft asphalt, taxi-way slope
• Engine thermal stabilization - warm up and cool down
• Pneumatic and electrical system requirements
• Slow/tight turns in direction of operating engine(s)
• Cross-bleed start requirements
Balance fuel conservation and safety considerations
One Engine Shut Down Considerations:
Fuel Conservation 75
Condition 727 737 747 757 767 777
Taxi*
(lb/min) 60 25 100 40 50 60
APU
(lb/min) 5 4 11 4 4 9
717
25
4
Sample Taxi and APU Fuel Burns
* Assumes all engines operating during taxi
Fuel Conservation 76
Takeoff
• Retract flaps as early as possible
• Full rate or derate to save fuel?
(Use of full rate will save fuel for a given takeoff, but general consensus is that in
the long-term, total costs will be reduced by using reduced takeoff thrust)
Fuel Conservation 77
-1.0%
-0.9%
-0.8%
-0.7%
-0.6%
-0.5%
-0.4%
-0.3%
-0.2%
-0.1%
0.0%
-25% -20% -15% -10% -5% 0%
Average takeoff thrust reduction (% from full rate)
Δ TSFC @ 1000 cycles
Estimated Reduced Thrust
Impact at 1000 Cycles
15% Average Thrust Reduction Can Improve
Overall TSFC at 1000 Cycles by over 0.4%
(Courtesy of Pratt & Whitney)
Reduced Take Off Thrust
Improves Long-term Performance Retention
Fuel Conservation 78
Distance
Altitude
Initial cruise
altitude
Cost index
increasing
A
B
CI = 0 (Min fuel)
Min time to Point B
Max gradient
Climb
Cost Index = 0 minimizes fuel to climb and
cruise to a common point in space
Fuel Conservation 79
Cruise
• A plane flying in steady, level flight may require
some control surface inputs to maintain lateraldirectional
control
• Use of the proper trim procedure
minimizes drag
• Poor trim procedure can
result in a 0.5% cruise
drag penalty on a 747
• Follow the procedures
provided in the Flight
Crew Training Manual
Lateral - Directional Trim Procedure
Fuel Conservation 80
Systems Management
Cruise
• A/C packs in high flow typically produce
a 0.5 - 1 % increase in fuel burn
• Do not use unnecessary cargo heat
• Do not use unnecessary anti-ice
• Maintain a balanced fuel load
Fuel Conservation 81
Winds
Cruise
• Wind may be a reason to choose an “off
optimum” altitude
• Want to maximize ground miles per unit
of fuel burned
• Wind-Altitude trade tables are provided
in the flight crew operations manual
Fuel Conservation 82
Fuel Mileage = =
Fuel Flow
VTAS
KG
NAM
Fuel Used = =
NGM/KG
NGM
NAM/KG
NAM =
VTAS + VWIND
(NGM) (Fuel Flow)
Ground Fuel Mileage = =
Fuel Flow
VTAS + VWIND
KG
NGM
In cruise: positive wind = Tailwind
negative wind = Headwind
VGround
Wind Effects On Fuel Mileage
Fuel Conservation 83
Typical Wind/Altitude Trade Table
Wind Effects On Cruise Altitude: Wind/Alt Trade
33 knots greater tailwind (or,
lower headwind) would be
required at FL310 relative to
FL350 to obtain equivalent
ground fuel mileage
Fuel Conservation 84
MACH number
Ground fuel mileage
.80 .81 .82 .83 .84 .85 .86
64
66
68
70
72
74
76
78
35K, Wind = 0
31K, Wind = 0
MACH number
Ground fuel mileage
.80 .81 .82 .83 .84 .85 .86
64
66
68
70
72
74
76
78
35K, Wind = 0
31K, Wind = 0
Wind = 10
Wind = 20
Wind = 30
Wind = 40
LRC, 35K
Typical Wind Altitude/Trade for Constant Airplane Weight
Example of increasing Tailwind at 31,000 ft Example of increasing headwind at 35,000 ft
LRC, 31K
LRC, 31K
LRC, 35K
Wind = -10
Wind = -20
Wind = -30
Wind = -40
Wind Effects On Cruise Altitude: Wind/Alt Trade
* Actual ground fuel mileage comparisons vary with airplane model,
weight, and altitudes considered
Fuel Conservation 85
Ground fuel mileage
60
80
100
120
140
160
180
200
220
240
.72 .73 .74 .75 .76 .77 .78 .79 .80 .81 .82
MACH number
Zero wind
100 kt headwind
200 kt headwind
100 kt tailwind
MRC
LRC
Typical affect of wind on ground fuel mileage when
flying a constant altitude and weight
Wind Effects On Cruise Mach Number
Zero wind LRC
* Actual ground fuel mileage comparisons vary with airplane model,
weight, and altitudes considered
Fuel Conservation 86
Descent
• Penalty for early descent - spend more time at low
altitudes, higher fuel burn
• Optimum top of descent point is affected by wind,
ATC, speed restrictions, etc.
• Use information provided by FMC
• Use idle thrust (no part-power descents)
Fuel Conservation 87
Distance
Final cruise
altitude
Cost index
increasing
B
CI = 0 (Min fuel)
Min time from point A to B
Descent
Cost Index = 0 minimizes fuel between a common
cruise point and a common end of descent point
Altitude
A
Fuel Conservation 88
Approach
• Do not transition to the landing configuration
too early
• Fuel flow in the landing configuration is
approximately 150% of the fuel flow in the
clean configuration
Fuel Conservation 89
Summary Of Operational Practices
• Minimize landing weight
• Do not carry more reserve fuel than required
• Use aft C.G. loading if possible
• Use lowest flap setting required
• Target optimum altitude (wind-corrected)
• Target LRC (or cost index)
• Choose most direct routing
• Use benefits of ETOPS routing
• Use tankering where appropriate
Flight Operations / Dispatchers
Fuel Conservation 90
Flight Crews
Summary Of Operational Practices
• Minimize engine/APU use on ground
• Retract Flaps as early as possible
• Fly the flight-planned speeds for all
phases of flight
• Use proper trim procedures
• Understand the airplane’s systems
• Understand wind/altitude trades
• Don’t descend too early (or too late)
• Don’t transition to landing configuration
too early
Maintenance Practices for
Fuel Conservation
Fuel Conservation 92
Opportunities For Fuel Conservation
Maintenance Personnel
• Airframe maintenance
• Engine maintenance
• Systems maintenance
Fuel Conservation 93
Excess Drag Is Lost Payload
Fuel Conservation 94
Exxcceessss Drraagg Meeaannss Waasstteedd Fuueell
• 747 ≈ 100,000
• 777 ≈ 70,000
• 767 ≈ 30,000
• 757 ≈ 25,000
• 737 ≈ 15,000
• 727 ≈ 30,000
1% Drag In Terms Of Gallons Per Year
* Assumes typical airplane utilization rates. Actual utilization rates may differ.
Fuel Conservation 95
Total Drag Is Composed Of:
Compressible drag ≈ drag due to Mach
• Shock waves, separated flow
Induced (vortex) drag ≈ drag due to lift
• Downwash behind wing, trim drag
Parasite drag ≈ drag not due to lift
• Shape of the body, skin friction, leakage,
interference between components
• Parasite drag includes excrescence drag
Fuel Conservation 96
Drag due to
airplane size
and weight
(unavoidable)
~ 90%
Pressure, trim and
interference drag
(optimized in the
wind tunnel)
~ 6%
Excrescence drag
(this can increase)
~ 4%
Contributors To Total Airplane Drag
(New Airplane at Cruise Conditions)
* Typical values for illustration purposes. Actual magnitudes vary with airplane model
Fuel Conservation 97
What Is Excrescence Drag?
The additional drag on the airplane due
to the sum of all deviations from a
smooth sealed external surface
Proper maintenance can prevent an
increase in excrescence drag
Fuel Conservation 98
0
1
2
3
4
Excrescence drag
(% airplane drag)
Discrete items
Mismatches
and gaps
Internal airflow & seal
leakage
Roughness &
surface irregularities
Excrescence Drag On
A ‘New Airplane’ Is Composed Of:
Total
* Typical values for illustration purposes. Actual magnitudes vary with airplane model
Fuel Conservation 99
Discrete Items
• Antennas, masts, lights
• Drag is a function of design, size, position
Fuel Conservation 100
Mismatched Surfaces
Steps and gaps at skin joints, around windows, doors,
control surfaces, and access panels
Frame
Skin
Fuel Conservation 101
Internal Airflow
Leaks from higher to lower
pressure areas due to
deteriorated or poorly-installed
aerodynamic seals
Aiirrffllow
Fuel Conservation 102
Roughness
(Particularly Bad Near Static Sources)
• Non-flush fasteners, rough surface
• Waviness, gaps
Non Flush Rivet Rough Surface
Waviness Gaps
Fuel Conservation 103
Most Important in Critical Areas
• Forward portion of fuselage and nacelle
• Leading areas of wings and tail
• Local Coefficient of Pressure (Cp) is highest
All spoilers up
3.75” = 2% drag
Outboard aileron up
4” = 1% drag
Rudder deflection
4.5 degrees
(offset 9.5” at base)
=2% drag
1” tall ridge on wing
75 ft. long = 2% drag
747 Cruise Drag Sensitivities
Fuel Conservation 104
Regular Maintenance Minimizes Deterioration
• Flight control rigging
• Misalignments and mismatches
• Aerodynamic seals
• Exterior surface finish
• OEW control
• Engine maintenance
• Instrument calibration
Fuel Conservation 105
Flight Control Rigging
Out of rig controls and flaps can cause a large
increase in fuel burn
747-400 examples:
• Aileron 1” out of rig ≈ 0.25% fuel
• Spoilers 1,2,3 and 4 up 2” ≈ 0.4% fuel
• Upper and lower rudder offset ≈ 0.35% fuel
• Inboard elevator 2” out of rig ≈ .4% fuel
Fuel Conservation 106
In-Flight Inspections Can be Easily Made
Several times during flight:
• Note required aileron and rudder trim ≈ 5 minutes
• Visual check of spoiler misfair ≈ 5 minutes
• Visual check of trailing edge of wing ≈ 10 minutes
Fuel Conservation 107
Misrigged Ailerons
Misrigged outboard ailerons can result
in an increase in drag and fuel flow
Fuel Conservation 108
Spoilers
The spoilers can begin to rise if the aircraft is
balanced by excessive autopilot lateral input
Fuel Conservation 109
Control Surface Rigging Check
747 example (includes fit and fair check):
• Ailerons ≈ 4 hours (1 - 2 people)
• Spoilers ≈ 2 hours (2 people)
• Flaps and Slats ≈ 3 hours (1 - 2 people)
• Rudders ≈ 3 hours (1 - 2 people)
• Elevators ≈ 2 hours (2 people)
Fuel Conservation 110
Misalignment, Mismatch
Check items which are adjustable and could
become misaligned after years of service:
• Adjustable panels
• Landing gear doors
• Entry doors and cargo doors
Fuel Conservation 111
Surface Mismatch
Surface Mismatch – ADF Antenna Fairing – negative step
Fuel Conservation 112
Surface Mismatch
Engine inlet secondary inlet door mismatch – positive step
Fuel Conservation 113
Leading Edge Mismatch
727 surface mismatch-R.H. Wing leading edge
slat actuator rod cover - positive step
Airflow
Fuel Conservation 114
Positive Step and Improper Seal
727 surface mismatch - lower wing critical area
(flap track fairing - fabricated leather seal) - positive step
Airflow
Fuel Conservation 115
Check for Tight Aircraft Doors
Note the tight and even fit of the air
conditioning compartment access doors
Fuel Conservation 116
Maintain Seals
• Passenger and cargo door seals
• Damaged seals allow air to leak out
• Lose ‘thrust recovery’ from outflow valves
• Disrupts flow along the fuselage
Passenger
doors
Fwd cargo
door seal
depressor
before repair
Fuel Conservation 117
Check for Missing or Damaged Seals
747 R.H. Wing gear well door forward
outboard seal missing and damaged
Airflow
Fuel Conservation 118
Check for Rough Surface Paint
747 rough paint - lower fuselage
Airflow
Fuel Conservation 119
Maintain a Clean Airplane
• Maintain surface finish
• Fluid leaks contribute to drag
• Periodic washing of exterior
is beneficial
– 0.1% drag reduction if
excessively dirty
– Minimizes metal corrosion
and paint damage
– Location of leaks and local
damage
• Customer aesthetics
Fuel Conservation 120
Make Simple Inspections
• Seal inspections ≈ 1 hour
• Nacelles and struts ≈ 2 hours
• Wing/body/tail misfairs ≈ 2 hours
• General roughness and appearance ≈ 1 hour
• Pressurized fuselage leak ≈ 2 hours
• Landing gear door check ≈ 1.5 hours
Fuel Conservation 121
Average Results Of In-service Drag Inspections
• Results of in-service airframe drag inspections show the
most common contributors to airframe deterioration are:
– Control surface miss-rigging
– Aerodynamic seal deterioration
• Lesser contributors include:
– Skin surface miss-matches
– Surface roughness
– ‘Other’
Fuel Conservation 122
OEW Control
• Operating empty weight (OEW) typically increases
0.1% to 0.2% per year, leveling off around +1% from
a new-airplane level in 5 to 10 years
• Most OEW growth is mainly due to accumulation of:
– Moisture
– Dirt
Fuel Conservation 123
Engine Maintenance
• Need to balance savings from performance
improvements versus cost to perform maintenance
• Maintenance performed on high and low pressure
turbines and compressors will help keep fuel
consumption from deteriorating
Fuel Conservation 124
Items That Cause Engine/Fuel Burn
deterioration
Erosion / Wear / Contamination
• Blade rubs - HP compressor, HP turbine, airfoil blade erosion
• Thermal distortion of blade parts
• Blade leading edge wear
• Excessive fan rubstrip wear
• Lining loss in the HP compressor
• Oil or dirt contamination of LP/HP compressor
Seals / Valves / Cooling
• Loss of High Pressure Turbine (HPT) outer air seal material
• Leaking thrust reverser seals
• ECS anomalies/leaks
• Failed-open fan air valves/Failed-open IDG air-oil cooler
valves
• Faulty turbine case cooling/Faulty 11th stage cooling valves
Fuel Conservation 125
Engine Components Are Affected By The
Environment In Which They Operate
Fuel Conservation 126
Typical Engine Deterioration Mechanisms
Increased tip
clearances
Seal leakage
Airfoil
erosion
Dirt
accumulation
(Courtesy of Pratt & Whitney)
Fuel Conservation 127
Scheduled Refurbishing Recovers SFC and EGT
(Courtesy of Pratt & Whitney)
SFC
or
EGT
Hours or cycles
Shop
visit
Shop
visit
Fuel Conservation 128
Simple Procedures Can Recover Performance
Between Scheduled Shop Visits
On-Wing Engine Washing
• Addresses dirt accumulation
On-Wing Engine Bleed Rigging
• Addresses leakage caused by bleed
system wear
(Courtesy of Pratt & Whitney)
Fuel Conservation 129
On-Wing Engine Washing
• Simple procedure
• Special tooling identified
• 3-4 hours, two mechanics
Up to 1.5% SFC
improvements
possible
Hand wash fan and
LPC stator vanes
Regular Intervals Ensure Fuel Economy
(Courtesy of Pratt & Whitney)
Fuel Conservation 130
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 1000 2000 3000 4000 5000 6000
Cycles
% ΔTSFC
1000 cycle wash
Unwashed
500 cycle wash
0.5%
1000 cycle wash
cumulative benefit
0.75%
500 cycle wash
cumulative benefit
Example of Water Wash Frequency Impact
SFC and EGT Can Be Recovered Between Shop
Visits Using Repetitive Engine Washes
(Courtesy of Pratt & Whitney)
Fuel Conservation 131
On-Wing Engine Bleed Rigging
• Simple procedure
• Start, stability, service bleeds
• Problem Identified from in-flight
performance trends
Up to 2.5% SFC benefit
possible
Repair of Leaking Bleed Valves Saves Fuel
(Courtesy of Pratt & Whitney)
Fuel Conservation 132
Instrument Calibration
• Speed measuring equipment has a large impact
on fuel mileage
• If speed is not accurate the airplane may be flying
faster or slower than intended
• On the 747-400, flying 0.01M faster can increase
fuel burn by 1% or more
Fuel Conservation 133
Airspeed System Error Penalty
• Keep airspeed system calibrated
• Airspeed reads 1% low, airplane flies 1% fast
• About 2% drag penalty in a 747
Fuel Conservation 134
Plugging or deforming the holes in the alternate static port can result
in erroneous instrument readings in the flight deck. Keeping the
circled area smooth and clean promotes aerodynamic efficiency.
Check Static Sources
Fuel Conservation 135
Don’t let this…
Become this!
Proper and Continuous Airframe and Engine Maintenance
Will Keep Your Airplanes Performing at Their Best!
Fuel Conservation 136
It Takes the Whole Team to Win
Conclusions
• Large fuel savings results from the accumulation
of many smaller fuel-saving actions and policies
• Dispatch, flight operations, flight crews, maintenance,
and management all need to contribute
• Program should be tailored to your airline’s needs and
requirements
Fuel Conservation 137
For More Information
• Airliner Magazine
– 1958 to 1997
• Newsletters (self-contained inserts in the Airliner Magazine)
– Fuel Conservation Newsletter - January 1981 to
December 1983
– Fuel Conservation & Operations Newsletter - January 1984
to June 1994
– Operations Newsletter - July 1994 to December 1997
• Aero Magazine (replaced Airliner after Boeing - MDC merger)
– January 1998 to 2003
Boeing has published numerous articles addressing fuel
conservation over the last 4 decades in the following publications:
End of
Fuel Conservation
Flight Operations Engineering
Boeing Commercial Airplanes
November 2004