AIM

帅哥

Turbulence Reporting Criteria Table Intensity Aircraft Reaction Reaction Inside Aircraft Reporting Term-Definition Light Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw). Report as Light Turbulence; 1 or Turbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude. Report as Light Chop. Occupants may feel a slight strain against seat belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may be con- ducted and little or no difficulty is encountered in walking. Occasional-Less than 1 /3 of the time. Intermittent-1 /3 to 2 /3. Continuous-More than 2 /3. Moderate Turbulence that is similar to Light Turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Report as Moderate Turbulence; 1 or Turbulence that is similar to Light Chop but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude. Report as Moderate Chop.1 Occupants feel definite strains against seat belts or shoulder straps. Unse- cured objects are dislodged. Food service and walking are difficult. NOTE 1. Pilots should report location(s), time (UTC), intensity, whether in or near clouds, altitude, type of aircraft and, when applicable, duration of turbulence. 2. Duration may be based on time between two locations or over a single location. All locations should be readily identifiable. Severe Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence. 1 Occupants are forced violently against seat belts or shoulder straps. Unse- cured objects are tossed about. Food Service and walking are impossible. EXAMPLES: a. Over Omaha. 1232Z, Moderate Turbulence, in cloud, Flight Level_310, B707. Extreme Turbulence in which the aircraft is violently tossed about and is practically impossible to control. It may cause structural damage. Report as Extreme Turbulence. 1 b. From 50 miles south of Albuquer- que to 30 miles north of Phoenix, 1210Z to 1250Z, occasional Moderate Chop, Flight Level 330, DC8. 1 High level turbulence (normally above 15,000 feet ASL) not associated with cumuliform cloudiness, including thunderstorms, should be reported as CAT (clear air turbulence) preceded by the appropriate intensity, or light or moderate chop. AIM 2/14/08 7-1-45 Meteorology 7-1-24. Wind Shear PIREPs a. Because unexpected changes in wind speed and direction can be hazardous to aircraft operations at low altitudes on approach to and departing from airports, pilots are urged to promptly volunteer reports to controllers of wind shear conditions they encounter. An advance warning of this information will assist other pilots in avoiding or coping with a wind shear on approach or departure. b. When describing conditions, use of the terms “negative” or “positive” wind shear should be avoided. PIREPs of “negative wind shear on final,” intended to describe loss of airspeed and lift, have been interpreted to mean that no wind shear was encountered. The recommended method for wind shear reporting is to state the loss or gain of airspeed and the altitudes at which it was encountered. EXAMPLE1. Denver Tower, Cessna 1234 encountered wind shear, loss of 20 knots at 400. 2. Tulsa Tower, American 721 encountered wind shear on final, gained 25 knots between 600 and 400 feet followed by loss of 40 knots between 400 feet and surface. 1. Pilots who are not able to report wind shear in these specific terms are encouraged to make reports in terms of the effect upon their aircraft. EXAMPLE- Miami Tower, Gulfstream 403 Charlie encountered an abrupt wind shear at 800 feet on final, max thrust required. 2. Pilots using Inertial Navigation Systems (INSs) should report the wind and altitude both above and below the shear level. 7-1-25. Clear Air Turbulence (CAT) PIREPs CAT has become a very serious operational factor to flight operations at all levels and especially to jet traffic flying in excess of 15,000 feet. The best available information on this phenomenon must come from pilots via the PIREP reporting procedures. All pilots encountering CAT conditions are urgently requested to report time, location, and intensity (light, moderate, severe, or extreme) of the element to the FAA facility with which they are maintaining radio contact. If time and conditions permit, elements should be reported according to the standards for other PIREPs and position reports. REFERENCE- AIM, PIREPs Relating to Turbulence, Paragraph 7-1-23. 7-1-26. Microbursts a. Relatively recent meteorological studies have confirmed the existence of microburst phenomenon. Microbursts are small scale intense downdrafts which, on reaching the surface, spread outward in all directions from the downdraft center. This causes the presence of both vertical and horizontal wind shears that can be extremely hazardous to all types and categories of aircraft, especially at low altitudes. Due to their small size, short life span, and the fact that they can occur over areas without surface precipita- tion, microbursts are not easily detectable using conventional weather radar or wind shear alert systems. b. Parent clouds producing microburst activity can be any of the low or middle layer convective cloud types. Note, however, that microbursts commonly occur within the heavy rain portion of thunderstorms, and in much weaker, benign appearing convective cells that have little or no precipitation reaching the ground. AIM 2/14/08 7-1-46 Meteorology FIG 7-1-13 Evolution of a Microburst T-5 Min T-2 Min T T 5 Min T 10 Min HEIGHT (feet) 10,000 5,000 WIND SPEED 10-20 knots > 20 knots SCALE (miles) 0 1 2 3 Vertical cross section of the evolution of a microburst wind field. T is the time of initial divergence at the surface. The shading refers to the vector wind speeds. Figure adapted from Wilson et al., 1984, Microburst Wind Structure and Evaluation of Doppler Radar for Wind Shear Detection, DOT/FAA Report No. DOT/FAA/PM-84/29, National Technical Information Service, Springfield, VA 37 pp. c. The life cycle of a microburst as it descends in a convective rain shaft is seen in FIG 7-1-13. An important consideration for pilots is the fact that the microburst intensifies for about 5 minutes after it strikes the ground. d. Characteristics of microbursts include: 1. Size. The microburst downdraft is typically less than 1 mile in diameter as it descends from the cloud base to about 1,000-3,000 feet above the ground. In the transition zone near the ground, the downdraft changes to a horizontal outflow that can extend to approximately 2 1 /2 miles in diameter. 2. Intensity. The downdrafts can be as strong as 6,000 feet per minute. Horizontal winds near the surface can be as strong as 45 knots resulting in a 90_knot shear (headwind to tailwind change for a traversing aircraft) across the microburst. These strong horizontal winds occur within a few hundred feet of the ground. 3. Visual Signs. Microbursts can be found almost anywhere that there is convective activity. They may be embedded in heavy rain associated with a thunderstorm or in light rain in benign appearing virga. When there is little or no precipitation at the surface accompanying the microburst, a ring of blowing dust may be the only visual clue of its existence. 4. Duration. An individual microburst will seldom last longer than 15 minutes from the time it strikes the ground until dissipation. The horizontal winds continue to increase during the first 5 minutes with the maximum intensity winds lasting approxi- mately 2-4 minutes. Sometimes microbursts are concentrated into a line structure, and under these conditions, activity may continue for as long as an hour. Once microburst activity starts, multiple microbursts in the same general area are not uncommon and should be expected. AIM 2/14/08 7-1-47 Meteorology FIG 7-1-14 Microburst Encounter During Takeoff A microburst encounter during takeoff. The airplane first encounters a headwind and experiences increasing performance (1), this is followed in short succession by a decreasing headwind component (2), a downdraft (3), and finally a strong tailwind (4), where 2 through 5 all result in decreasing performance of the airplane. Position (5) represents an extreme situation just prior to impact. Figure courtesy of Walter Frost, FWG Associates, Inc., Tullahoma, Tennessee. e. Microburst wind shear may create a severe hazard for aircraft within 1,000 feet of the ground, particularly during the approach to landing and landing and take-off phases. The impact of a microburst on aircraft which have the unfortunate experience of penetrating one is characterized in FIG 7-1-14. The aircraft may encounter a headwind (performance increasing) followed by a downdraft and tailwind (both performance decreasing), possibly resulting in terrain impact. AIM 2/14/08 7-1-48 Meteorology FIG 7-1-15 NAS Wind Shear Product Systems f. Detection of Microbursts, Wind Shear and Gust Fronts. 1. FAA's Integrated Wind Shear Detection Plan. (a) The FAA currently employs an integrated plan for wind shear detection that will significantly improve both the safety and capacity of the majority of the airports currently served by the air carriers. This plan integrates several programs, such as the Integrated Terminal Weather System (ITWS), Terminal Doppler Weather Radar (TDWR), Weather System Processor (WSP), and Low Level Wind Shear Alert Systems (LLWAS) into a single strategic concept that significantly improves the aviation weather information in the terminal area. (See FIG 7-1-15.) (b) The wind shear/microburst information and warnings are displayed on the ribbon display terminals (RBDT) located in the tower cabs. They are identical (and standardized) in the LLWAS, TDWR and WSP systems, and so designed that the controller does not need to interpret the data, but simply read the displayed information to the pilot. The RBDTs are constantly monitored by the controller to ensure the rapid and timely dissemination of any hazardous event(s) to the pilot. AIM 2/14/08 7-1-49 Meteorology FIG 7-1-16 LLWAS Siting Criteria (c) The early detection of a wind shear/ micro-burst event, and the subsequent warning(s) issued to an aircraft on approach or departure, will alert the pilot/crew to the potential of, and to be prepared for, a situation that could become very dangerous! Without these warnings, the aircraft may NOT be able to climb out of, or safely transition, the event, resulting in a catastrophe. The air carriers, working with the FAA, have developed specialized training programs using their simulators to train and prepare their pilots on the demanding aircraft procedures required to escape these very dangerous wind shear and/or microburst encounters. 2. Low Level Wind Shear Alert System (LLWAS). (a) The LLWAS provides wind data and software processes to detect the presence of hazardous wind shear and microbursts in the vicinity of an airport. Wind sensors, mounted on poles sometimes as high as 150 feet, are (ideally) located 2,000 - 3,500 feet, but not more than 5,000 feet, from the centerline of the runway. (See FIG 7-1-16.) AIM 2/14/08 7-1-50 Meteorology FIG 7-1-17 Warning Boxes (b) LLWAS was fielded in 1988 at 110_air- ports across the nation. Many of these systems have been replaced by new TDWR and WSP technology. Eventually all LLWAS systems will be phased out; however, 39 airports will be upgraded to the LLWAS-NE (Network Expansion) system, which employs the very latest software and sensor technology. The new LLWAS-NE systems will not only provide the controller with wind shear warnings and alerts, including wind shear/microburst detection at the airport wind sensor location, but will also provide the location of the hazards relative to the airport runway(s). It will also have the flexibility and capability to grow with the airport as new runways are built. As many as 32 sensors, strategically located around the airport and in relationship to its runway configuration, can be accommodated by the LLWAS-NE network. 3. Terminal Doppler Weather Radar (TDWR). (a) TDWRs are being deployed at 45_loca- tions across the U.S. Optimum locations for TDWRs are 8 to 12 miles off of the airport proper, and designed to look at the airspace around and over the airport to detect microbursts, gust fronts, wind shifts and precipitation intensities. TDWR products advise the controller of wind shear and microburst events impacting all runways and the areas 1 /2 mile on either side of the extended centerline of the runways out to 3 miles on final approach and 2 miles out on departure. (FIG 7-1-17 is a theoretical view of the warning boxes, including the runway, that the software uses in determining the location(s) of wind shear or microbursts). These warnings are displayed (as depicted in the examples in subparagraph 5) on the RBDT. (b) It is very important to understand what TDWR does NOT DO: (1) It_DOES NOT warn of wind shear outside of the alert boxes (on the arrival and departure ends of the runways); (2) It_DOES NOT detect wind shear that is NOT a microburst or a gust front; (3) It_DOES NOT detect gusty or cross wind conditions; and (4) It DOES NOT detect turbulence. However, research and development is continuing on these systems. Future improvements may include such areas as storm motion (movement), improved AIM 2/14/08 7-1-51 Meteorology gust front detection, storm growth and decay, microburst prediction, and turbulence detection. (c) TDWR also provides a geographical situation display (GSD) for supervisors and traffic management specialists for planning purposes. The GSD displays (in color) 6 levels of weather (precipitation), gust fronts and predicted storm movement(s). This data is used by the tower supervisor(s), traffic management specialists and controllers to plan for runway changes and arrival/departure route changes in order to both reduce aircraft delays and increase airport capacity. 4. Weather System Processor (WSP). (a) The WSP provides the controller, supervi- sor, traffic management specialist, and ultimately the pilot, with the same products as the terminal doppler weather radar (TDWR) at a fraction of the cost of a TDWR. This is accomplished by utilizing new technologies to access the weather channel capabili- ties of the existing ASR-9 radar located on or near the airport, thus eliminating the requirements for a separate radar location, land acquisition, support facilities and the associated communication landlines and expenses. (b) The WSP utilizes the same RBDT display as the TDWR and LLWAS, and, just like TDWR, also has a GSD for planning purposes by supervisors, traffic management specialists and controllers. The WSP GSD emulates the TDWR display, i.e., it also depicts 6 levels of precipitation, gust fronts and predicted storm movement, and like the TDWR GSD, is used to plan for runway changes and arrival/depar- ture route changes in order to reduce aircraft delays and to increase airport capacity. (c) This system is currently under develop- ment and is operating in a developmental test status at the Albuquerque, New Mexico, airport. When fielded, the WSP is expected to be installed at 34_airports across the nation, substantially increasing the safety of the American flying public. 5. Operational aspects of LLWAS, TDWR and WSP. To demonstrate how this data is used by both the controller and the pilot, 3 ribbon display examples and their explanations are presented: (a) MICROBURST ALERTS EXAMPLE- This is what the controller sees on his/her ribbon display in the tower cab. 27A MBA 35K- 2MF 250 20 NOTE(See FIG 7-1-18 to see how the TDWR/WSP determines the microburst location). This is what the controller will say when issuing the alert. PHRASEOLOGY- RUNWAY 27 ARRIVAL, MICROBURST ALERT, 35 KT LOSS 2 MILE FINAL, THRESHOLD WIND 250 AT 20. In plain language, the controller is telling the pilot that on approach to runway 27, there is a microburst alert on the approach lane to the runway, and to anticipate or expect a 35 knot loss of airspeed at approximately 2 miles out on final approach (where it will first encounter the phenomena). With that information, the aircrew is forewarned, and should be prepared to apply wind shear/microburst escape procedures should they decide to continue the approach. Additionally, the surface winds at the airport for landing runway 27 are reported as 250_degrees at 20 knots. NOTE- Threshold wind is at pilot's request or as deemed appropriate by the controller. REFERENCE- FAA Order JO 7110.65, Air Traffic Control, Low Level Wind Shear/Microburst Advisories, Paragraph 3-1-8b2(a). AIM 2/14/08 7-1-52 Meteorology FIG 7-1-18 Microburst Alert (b) WIND SHEAR ALERTS EXAMPLE- This is what the controller sees on his/her ribbon display in the tower cab. 27A WSA 20K- 3MF 200 15 NOTE(See FIG 7-1-19 to see how the TDWR/WSP determines the wind shear location). This is what the controller will say when issuing the alert. PHRASEOLOGY- RUNWAY 27 ARRIVAL, WIND SHEAR ALERT, 20 KT LOSS 3 MILE FINAL, THRESHOLD WIND 200 AT 15. In plain language, the controller is advising the aircraft arriving on runway 27 that at about 3 miles out they can expect to encounter a wind shear condition that will decrease their airspeed by 20 knots and possibly encounter turbulence. Additionally, the airport surface winds for landing runway 27 are reported as 200 degrees at 15 knots. NOTE- Threshold wind is at pilot's request or as deemed appropriate by the controller. REFERENCE- FAA Order JO 7110.65, Air Traffic Control, Low Level Wind Shear/Microburst Advisories, Paragraph 3-1-8b2(a). AIM 2/14/08 7-1-53 Meteorology FIG 7-1-19 Weak Microburst Alert AIM 2/14/08 7-1-54 Meteorology FIG 7-1-20 Gust Front Alert (c) MULTIPLE WIND SHEAR ALERTS EXAMPLE- This is what the controller sees on his/her ribbon display in the tower cab. 27A WSA 20K+ RWY 250 20 27D WSA 20K+ RWY 250 20 NOTE(See FIG 7-1-20 to see how the TDWR/WSP determines the gust front/wind shear location.) This is what the controller will say when issuing the alert. PHRASEOLOGY- MULTIPLE WIND SHEAR ALERTS. RUNWAY 27 ARRIVAL, WIND SHEAR ALERT, 20 KT GAIN ON RUNWAY; RUNWAY 27 DEPARTURE, WIND SHEAR ALERT, 20 KT GAIN ON RUNWAY, WIND 250 AT 20. EXAMPLE- In this example, the controller is advising arriving and departing aircraft that they could encounter a wind shear condition right on the runway due to a gust front (significant change of wind direction) with the possibility of a 20 knot gain in airspeed associated with the gust front. Additionally, the airport surface winds (for the runway in use) are reported as 250 degrees at 20 knots. REFERENCE- FAA Order JO 7110.65, Air Traffic Control, Low Level Wind Shear/Microburst Advisories, Paragraph 3-1-8b2(d). AIM 2/14/08 7-1-55 Meteorology 6. The Terminal Weather Information for Pilots System (TWIP). (a) With the increase in the quantity and quality of terminal weather information available through TDWR, the next step is to provide this information directly to pilots rather than relying on voice communications from ATC. The National Airspace System has long been in need of a means of delivering terminal weather information to the cockpit more efficiently in terms of both speed and accuracy to enhance pilot awareness of weather hazards and reduce air traffic controller workload. With the TWIP capability, terminal weather information, both alphanumerically and graphically, is now available directly to the cockpit on a test basis at 9 locations. (b) TWIP products are generated using weather data from the TDWR or the Integrated Terminal Weather System (ITWS) testbed. TWIP products are generated and stored in the form of text and character graphic messages. Software has been developed to allow TDWR or ITWS to format the data and send the TWIP products to a database resident at Aeronautical Radio, Inc. (ARINC). These products can then be accessed by pilots using the ARINC Aircraft Communications Addressing and Reporting System (ACARS) data link services. Airline dispatchers can also access this database and send messages to specific aircraft whenever wind shear activity begins or ends at an airport. (c) TWIP products include descriptions and character graphics of microburst alerts, wind shear alerts, significant precipitation, convective activity within 30 NM surrounding the terminal area, and expected weather that will impact airport operations. During inclement weather, i.e., whenever a predeter- mined level of precipitation or wind shear is detected within 15 miles of the terminal area, TWIP products are updated once each minute for text messages and once every five minutes for character graphic messages. During good weather (below the predeter- mined precipitation or wind shear parameters) each message is updated every 10 minutes. These products are intended to improve the situational awareness of the pilot/flight crew, and to aid in flight planning prior to arriving or departing the terminal area. It is important to understand that, in the context of TWIP, the predetermined levels for inclement versus good weather has nothing to do with the criteria for VFR/MVFR/IFR/LIFR; it only deals with precipita- tion, wind shears and microbursts. 7-1-27. PIREPs Relating to Volcanic Ash Activity a. Volcanic eruptions which send ash into the upper atmosphere occur somewhere around the world several times each year. Flying into a volcanic ash cloud can be extremely dangerous. At least two B747s have lost all power in all four engines after such an encounter. Regardless of the type aircraft, some damage is almost certain to ensue after an encounter with a volcanic ash cloud.

帅哥

b. While some volcanoes in the U.S. are monitored, many in remote areas are not. These unmonitored volcanoes may erupt without prior warning to the aviation community. A pilot observing a volcanic eruption who has not had previous notification of it may be the only witness to the eruption. Pilots are strongly encouraged to transmit a PIREP regarding volcanic eruptions and any observed volcanic ash clouds. c. Pilots should submit PIREPs regarding volcanic activity using the Volcanic Activity Reporting (VAR) form as illustrated in Appendix 2. If a VAR form is not immediately available, relay enough information to identify the position and type of volcanic activity. d. Pilots should verbally transmit the data required in items 1 through 8 of the VAR as soon as possible. The data required in items 9 through 16 of the VAR should be relayed after landing if possible. 7-1-28. Thunderstorms a. Turbulence, hail, rain, snow, lightning, sus- tained updrafts and downdrafts, icing conditions-all are present in thunderstorms. While there is some evidence that maximum turbulence exists at the middle level of a thunderstorm, recent studies show little variation of turbulence intensity with altitude. b. There is no useful correlation between the external visual appearance of thunderstorms and the severity or amount of turbulence or hail within them. The visible thunderstorm cloud is only a portion of a turbulent system whose updrafts and downdrafts often extend far beyond the visible storm cloud. Severe turbulence can be expected up to 20 miles from severe thunderstorms. This distance decreases to about 10 miles in less severe storms. AIM 2/14/08 7-1-56 Meteorology c. Weather radar, airborne or ground based, will normally reflect the areas of moderate to heavy precipitation (radar does not detect turbulence). The frequency and severity of turbulence generally increases with the radar reflectivity which is closely associated with the areas of highest liquid water content of the storm. NO FLIGHT PATH THROUGH AN AREA OF STRONG OR VERY STRONG RADAR ECHOES SEPARATED BY 20-30 MILES OR LESS MAY BE CONSIDERED FREE OF SEVERE TURBULENCE. d. Turbulence beneath a thunderstorm should not be minimized. This is especially true when the relative humidity is low in any layer between the surface and 15,000 feet. Then the lower altitudes may be characterized by strong out flowing winds and severe turbulence. e. The probability of lightning strikes occurring to aircraft is greatest when operating at altitudes where temperatures are between minus 5 degrees Celsius and plus 5 degrees Celsius. Lightning can strike aircraft flying in the clear in the vicinity of a thunderstorm. f. METAR reports do not include a descriptor for severe thunderstorms. However, by understanding severe thunderstorm criteria, i.e., 50 knot winds or 3 /4_inch hail, the information is available in the report to know that one is occurring. g. Current weather radar systems are able to objectively determine precipitation intensity. These precipitation intensity areas are described as “light,” “moderate,” “heavy,” and “extreme.” REFERENCE- Pilot/Controller Glossary, Precipitation Radar Weather Descriptions. EXAMPLE1. Alert provided by an ATC facility to an aircraft: (aircraft identification) EXTREME precipitation between ten o'clock and two o'clock, one five miles. Precipitation area is two five miles in diameter. 2. Alert provided by an AFSS/FSS: (aircraft identification) EXTREME precipitation two zero miles west of Atlanta V-O-R, two five miles wide, moving east at two zero knots, tops flight level three niner zero. 7-1-29. Thunderstorm Flying a. Above all, remember this: never regard any thunderstorm “lightly” even when radar observers report the echoes are of light intensity. Avoiding thunderstorms is the best policy. Following are some Do's and Don'ts of thunderstorm avoidance: 1. Don't land or takeoff in the face of an approaching thunderstorm. A sudden gust front of low level turbulence could cause loss of control. 2. Don't attempt to fly under a thunderstorm even if you can see through to the other side. Turbulence and wind shear under the storm could be disastrous. 3. Don't fly without airborne radar into a cloud mass containing scattered embedded thunderstorms. Scattered thunderstorms not embedded usually can be visually circumnavigated. 4. Don't trust the visual appearance to be a reliable indicator of the turbulence inside a thunderstorm. 5. Do avoid by at least 20 miles any thunderstorm identified as severe or giving an intense radar echo. This is especially true under the anvil of a large cumulonimbus. 6. Do clear the top of a known or suspected severe thunderstorm by at least 1,000 feet altitude for each 10 knots of wind speed at the cloud top. This should exceed the altitude capability of most aircraft. 7. Do circumnavigate the entire area if the area has 6 /10 thunderstorm coverage. 8. Do remember that vivid and frequent lightning indicates the probability of a strong thunderstorm. 9. Do regard as extremely hazardous any thunderstorm with tops 35,000 feet or higher whether the top is visually sighted or determined by radar. b. If you cannot avoid penetrating a thunderstorm, following are some Do's before entering the storm: 1. Tighten your safety belt, put on your shoulder harness if you have one and secure all loose objects. 2. Plan and hold your course to take you through the storm in a minimum time. AIM 2/14/08 7-1-57 Meteorology 3. To avoid the most critical icing, establish a penetration altitude below the freezing level or above the level of minus 15 degrees Celsius. 4. Verify that pitot heat is on and turn on carburetor heat or jet engine anti-ice. Icing can be rapid at any altitude and cause almost instantaneous power failure and/or loss of airspeed indication. 5. Establish power settings for turbulence penetration airspeed recommended in your aircraft manual. 6. Turn up cockpit lights to highest intensity to lessen temporary blindness from lightning. 7. If using automatic pilot, disengage altitude hold mode and speed hold mode. The automatic altitude and speed controls will increase maneuvers of the aircraft thus increasing structural stress. 8. If using airborne radar, tilt the antenna up and down occasionally. This will permit you to detect other thunderstorm activity at altitudes other than the one being flown. c. Following are some Do's and Don'ts during the thunderstorm penetration: 1. Do keep your eyes on your instruments. Looking outside the cockpit can increase danger of temporary blindness from lightning. 2. Don't change power settings; maintain settings for the recommended turbulence penetration airspeed. 3. Don't attempt to maintain constant altitude; let the aircraft “ride the waves.” 4. Don't turn back once you are in the thunderstorm. A straight course through the storm most likely will get you out of the hazards most quickly. In addition, turning maneuvers increase stress on the aircraft. AIM 2/14/08 7-1-58 Meteorology 7-1-30. Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report (METAR) FIG 7-1-21 Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report (METAR) (Front) U.S. Department of Transportation Federal Aviation Administration KEY to AERODROME FORECAST (TAF) and AVIATION ROUTINE WEATHER REPORT (METAR) (FRONT) TAF KPIT 091730Z 091818 15005KT 5SM HZ FEW020 WS010/31022KT FM 1930 30015G25KT 3SM SHRA OVC015 TEMPO 2022 1/2SM +TSRA OVC008CB FM0100 27008KT 5SM SHRA BKN020 OVC040 PROB40 0407 1SM -RA BR FM1015 18005KT 6SM -SHRA OVC020 BECMG 1315 P6SM NSW SKC METAR KPIT 091955Z COR 22015G25KT 3/4SM R28L/2600FT TSRA OVC010CB 18/16 A2992 RMK SLP045 T01820159 FORECAST EXPLANATION REPORT TAF Message type : TAF-routine or TAF AMD-amended forecast, METAR-hourly, SPECI-special or TESTM-non-commissioned ASOS report METAR KPIT ICAO location indicator KPIT 091730Z Issuance time: ALL times in UTC “Z”, 2-digit date, 4-digit time 091955z 091818 Valid period: 2-digit date, 2-digit beginning, 2-digit ending times In U.S. METAR: CORrected of; or AUTOmated ob for automated report with no human intervention; omitted when observer logs on COR 15005KT Wind: 3 digit true-north direction , nearest 10 degrees (or VaRiaBle); next 2-3 digits for speed and unit, KT (KMH or MPS); as needed, Gust and maximum speed; 00000KT for calm; for METAR, if direction varies 60 degrees or more, Variability appended, e.g., 180V260 22015G25KT 5SM Prevailing visibility; in U.S., Statute Miles & fractions; above 6 miles in TAF Plus6SM. (Or, 4-digit minimum visibility in meters and as required, lowest value with direction) 3/4SM Runway Visual Range: R; 2-digit runway designator Left, Center, or Right as needed; “/”, Minus or Plus in U.S., 4-digit value, FeeT in U.S., (usually meters elsewhere); 4-digit value Variability 4-digit value (and tendency Down, Up or No change) R28L/2600FT HZ Significant present, forecast and recent weather: see table (on back) TSRA FEW020 Cloud amount, height and type: Sky Clear 0/8, FEW >0/8-2/8, SCaTtered 3/8-4/8, BroKeN 5/8-7/8, OVerCast 8/8; 3-digit height in hundreds of ft; Towering Cumulus or CumulonimBus in METAR; in TAF, only CB. Vertical Visibility for obscured sky and height “VV004”. More than 1 layer may be reported or forecast. In automated METAR reports only, CLeaR for “clear below 12,000 feet” OVC 010CB Temperature: degrees Celsius; first 2 digits, temperature “/” last 2 digits, dew-point temperature; Minus for below zero, e.g., M06 18/16 Altimeter setting: indicator and 4 digits; in U.S., A-inches and hundredths; (Q-hectoPascals, e.g., Q1013) A2992 AIM 2/14/08 7-1-59 Meteorology FIG 7-1-22 Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report (METAR) (Back) U.S. Department of Transportation Federal Aviation Administration KEY to AERODROME FORECAST (TAF) and AVIATION ROUTINE WEATHER REPORT (METAR) (BACK) FORECAST EXPLANATION REPORT WS010/31022KT In U.S. TAF, non-convective low-level (2,000 ft) Wind Shear; 3-digit height (hundreds of ft); “/”; 3-digit wind direction and 2-3 digit wind speed above the indicated height, and unit, KT In METAR, ReMarK indicator & remarks. For example: Sea- Level Pressure in hectoPascals & tenths, as shown: 1004.5 hPa; Temp/dew-point in tenths _C, as shown: temp. 18.2_C, dew-point 15.9_C RMK SLP045 T01820159 FM1930 FroM and 2-digit hour and 2-digit minute beginning time: indicates significant change. Each FM starts on a new line, indented 5 spaces TEMPO 2022 TEMPOrary: changes expected for <1 hour and in total, < half of 2-digit hour beginning and 2-digit hour ending time period PROB40 0407 PROBability and 2-digit percent (30 or 40): probable condition during 2-digit hour beginning and 2-digit hour ending time period BECMG 1315 BECoMinG: change expected during 2-digit hour beginning and 2-digit hour ending time period Table of Significant Present, Forecast and Recent Weather- Grouped in categories and used in the order listed below; or as needed in TAF, No Significant Weather. QUALIFIER INTENSITY OR PROXIMITY `-' Light “no sign” Moderate `+' Heavy VC Vicinity: but not at aerodrome; in U.S. METAR, between 5 and 10SM of the point(s) of observation; in U.S. TAF, 5 to 10SM from center of runway complex (elsewhere within 8000m) DESCRIPTOR MI Shallow BC Patches PR Partial TS Thunderstorm BL Blowing SH Showers DR Drifting FZ Freezing WEATHER PHENOMENA PRECIPITATION DZ Drizzle RA Rain SN Snow SG Snow grains IC Ice Crystals PL Ice Pellets GR Hail GS Small hail/snow UP Unknown precipitation in automated observations pellets OBSCURATION BR Mist (5/8SM) FG Fog (<5/8SM) FU Smoke VA Volcanic ash SA Sand HZ Haze PY Spray DU Widespread dust OTHER SQ Squall SS Sandstorm DU Duststorm PO Well developed FC Funnel cloud +FC tornado/waterspout dust/sand whirls -Explanations in parentheses “( )” indicate different worldwide practices. - Ceiling is not specified; defined as the lowest broken or overcast layer, or the vertical visibility. - NWS TAFs exclude turbulence, icing & temperature forecasts; NWS METARs exclude trend forecasts January 1999 Department of Transportation Aviation Weather Directorate FEDERAL AVIATION ADMINISTRATION AIM 2/14/08 7-1-60 Meteorology 7-1-31. International Civil Aviation Organization (ICAO) Weather Formats The U.S. uses the ICAO world standard for aviation weather reporting and forecasting. The utilization of terminal forecasts affirms our commitment to a single global format for aviation weather. The World Meteorological Organization's (WMO) publication No. 782 “Aerodrome Reports and Forecasts” contains the base METAR and TAF code as adopted by the WMO member countries. a. Although the METAR code is adopted worldwide, each country is allowed to make modifications or exceptions to the code for use in their particular country, e.g., the U.S. will continue to use statute miles for visibility, feet for RVR values, knots for wind speed, and inches of mercury for altimetry. However, temperature and dew point will be reported in degrees Celsius. The U.S. will continue reporting prevailing visibility rather than lowest sector visibility. Most of the current U.S. observing procedures and policies will continue after the METAR conversion date, with the information disseminated in the METAR code and format. The elements in the body of a METAR report are separated with a space. The only exceptions are RVR, temperature and dew point, which are separated with a solidus (/). When an element does not occur, or cannot be observed, the preceding space and that element are omitted from that particular report. A METAR report contains the following sequence of elements in the following order: 1. Type of report. 2. ICAO Station Identifier. 3. Date and time of report. 4. Modifier (as required). 5. Wind. 6. Visibility. 7. Runway Visual Range (RVR). 8. Weather phenomena. 9. Sky conditions. 10. Temperature/dew point group. 11. Altimeter. 12. Remarks (RMK). b. The following paragraphs describe the ele- ments in a METAR report. 1. Type of report. There are two types of report: (a) Aviation Routine Weather Report (METAR); and (b) Nonroutine (Special) Aviation Weather Report (SPECI). The type of report (METAR or SPECI) will always appear as the lead element of the report. 2. ICAO Station Identifier. The METAR code uses ICAO 4-letter station identifiers. In the contiguous 48 States, the 3-letter domestic station identifier is prefixed with a “K;” i.e., the domestic identifier for Seattle is SEA while the ICAO identifier is KSEA. Elsewhere, the first two letters of the ICAO identifier indicate what region of the world and country (or state) the station is in. For Alaska, all station identifiers start with “PA;” for Hawaii, all station identifiers start with “PH.” Canadian station identifiers start with “CU,” “CW,” “CY,” and “CZ.” Mexican station identifiers start with “MM.” The identifier for the western Caribbean is “M” followed by the individual country's letter; i.e., Cuba is “MU;” Dominican Republic “MD;” the Bahamas “MY.” The identifier for the eastern Caribbean is “T” followed by the individual country's letter; i.e., Puerto Rico is “TJ.” For a complete worldwide listing see ICAO Document 7910, Location Indicators. 3. Date and Time of Report. The date and time the observation is taken are transmitted as a six-digit date/time group appended with Z to denote Coordinated Universal Time (UTC). The first two digits are the date followed with two digits for hour and two digits for minutes. EXAMPLE172345Z (the 17th day of the month at 2345Z) 4. Modifier (As Required). “AUTO” identi- fies a METAR/SPECI report as an automated weather report with no human intervention. If “AUTO” is shown in the body of the report, the type of sensor equipment used at the station will be encoded in the remarks section of the report. The absence of “AUTO” indicates that a report was made manually by an observer or that an automated report had human augmentation/backup. The modifier “COR” indi- cates a corrected report that is sent out to replace an earlier report with an error. AIM 2/14/08 7-1-61 Meteorology NOTE- There are two types of automated stations, AO1 for automated weather reporting stations without a precipita- tion discriminator, and AO2 for automated stations with a precipitation discriminator. (A precipitation discriminator can determine the difference between liquid and frozen/freezing precipitation). This information appears in the remarks section of an automated report. 5. Wind. The wind is reported as a five digit group (six digits if speed is over 99 knots). The first three digits are the direction the wind is blowing from, in tens of degrees referenced to true north, or “VRB” if the direction is variable. The next two digits is the wind speed in knots, or if over 99 knots, the next three digits. If the wind is gusty, it is reported as a “G” after the speed followed by the highest gust reported. The abbreviation “KT” is appended to denote the use of knots for wind speed. EXAMPLE13008KT - wind from 130 degrees at 8 knots 08032G45KT - wind from 080 degrees at 32 knots with gusts to 45 knots VRB04KT - wind variable in direction at 4 knots 00000KT - wind calm 210103G130KT - wind from 210 degrees at 103 knots with gusts to 130 knots If the wind direction is variable by 60 degrees or more and the speed is greater than 6 knots, a variable group consisting of the extremes of the wind direction separated by a “v” will follow the prevailing wind group. 32012G22KT 280V350 (a) Peak Wind. Whenever the peak wind exceeds 25 knots “PK WND” will be included in Remarks, e.g., PK WND 28045/1955 “Peak wind two eight zero at four five occurred at one niner five five.” If the hour can be inferred from the report time, only the minutes will be appended, e.g., PK WND 34050/38 “Peak wind three four zero at five zero occurred at three eight past the hour.” (b) Wind shift. Whenever a wind shift occurs, “WSHFT” will be included in remarks followed by the time the wind shift began, e.g., WSHFT 30 FROPA “Wind shift at three zero due to frontal passage.” 6. Visibility. Prevailing visibility is reported in statute miles with “SM” appended to it. EXAMPLE7SM - seven statute miles 15SM - fifteen statute miles 1 /2SM - one-half statute mile (a) Tower/surface visibility. If either visi- bility (tower or surface) is below four statute miles, the lesser of the two will be reported in the body of the report; the greater will be reported in remarks. (b) Automated visibility. ASOS visibility stations will show visibility ten or greater than ten miles as “10SM.” AWOS visibility stations will show visibility less than 1 /4 statute mile as “M 1 /4SM” and visibility ten or greater than ten miles as “10SM.” (c) Variable visibility. Variable visibility is shown in remarks (when rapid increase or decrease by 1 /2 statute mile or more and the average prevailing visibility is less than three miles) e.g., VIS 1V2 “visibility variable between one and two.” (d) Sector visibility. Sector visibility is shown in remarks when it differs from the prevailing visibility, and either the prevailing or sector visibility is less than three miles. EXAMPLE- VIS N2 - visibility north two 7. Runway Visual Range (When Reported). “R” identifies the group followed by the runway heading (and parallel runway designator, if needed) “/” and the visual range in feet (meters in other countries) followed with “FT” (feet is not spoken). (a) Variability Values. When RVR varies (by more than on reportable value), the lowest and highest values are shown with “V” between them. (b) Maximum/Minimum Range. “P” indi- cates an observed RVR is above the maximum value for this system (spoken as “more than”). “M” indicates an observed RVR is below the minimum value which can be determined by the system (spoken as “less than”). EXAMPLE- R32L/1200FT - runway three two left R-V-R one thousand two hundred. R27R/M1000V4000FT - runway two seven right R-V-R variable from less than one thousand to four thousand. AIM 2/14/08 7-1-62 Meteorology 8. Weather Phenomena. The weather as reported in the METAR code represents a significant change in the way weather is currently reported. In METAR, weather is reported in the format: Intensity/Proximity/Descriptor/Precipitation/ Obstruction to visibility/Other NOTE- The “/” above and in the following descriptions (except as the separator between the temperature and dew point) are for separation purposes in this publication and do not appear in the actual METARs. (a) Intensity applies only to the first type of precipitation reported. A “-” denotes light, no symbol denotes moderate, and a “+” denotes heavy. (b) Proximity applies to and reported only for weather occurring in the vicinity of the airport (between 5 and 10 miles of the point(s) of observation). It is denoted by the letters “VC.” (Intensity and “VC” will not appear together in the weather group). (c) Descriptor. These eight descriptors ap- ply to the precipitation or obstructions to visibility: TS thunderstorm . . . . . . . . . . . DR low drifting . . . . . . . . . . . SH showers . . . . . . . . . . . MI shallow . . . . . . . . . . . FZ freezing . . . . . . . . . . . BC patches . . . . . . . . . . . BL blowing . . . . . . . . . . . PR partial . . . . . . . . . . . NOTE- Although “TS” and “SH” are used with precipitation and may be preceded with an intensity symbol, the intensity still applies to the precipitation, not the descriptor. (d) Precipitation. There are nine types of precipitation in the METAR code: RA rain . . . . . . . . . . DZ drizzle . . . . . . . . . . SN snow . . . . . . . . . . GR hail (1 /4” or greater) . . . . . . . . . . GS small hail/snow pellets . . . . . . . . . . PL ice pellets . . . . . . . . . . SG snow grains . . . . . . . . . . IC ice crystals (diamond dust) . . . . . . . . . . . UP unknown precipitation . . . . . . . . . . (automated stations only) (e) Obstructions to visibility. There are eight types of obscuration phenomena in the METAR code (obscurations are any phenomena in the atmosphere, other than precipitation, that reduce horizontal visibility): FG fog (vsby less than 5 /8 mile) . . . . . . . . . . HZ haze . . . . . . . . . . FU smoke . . . . . . . . . . PY spray . . . . . . . . . . BR mist (vsby 5 /8 - 6 miles) . . . . . . . . . . SA sand . . . . . . . . . . DU dust . . . . . . . . . . VA volcanic ash . . . . . . . . . . NOTE- Fog (FG) is observed or forecast only when the visibility is less than five-eighths of mile, otherwise mist (BR) is observed or forecast. (f) Other. There are five categories of other weather phenomena which are reported when they occur: SQ squall . . . . . . . . . . . SS sandstorm . . . . . . . . . . . DS duststorm . . . . . . . . . . . PO dust/sand whirls . . . . . . . . . . FC funnel cloud . . . . . . . . . . . +FC tornado/waterspout . . . . . . . . . Examples: TSRA thunderstorm with moderate . . . . . . . . . rain +SN heavy snow . . . . . . . . . . -RA FG light rain and fog . . . . . . . BRHZ mist and haze . . . . . . . . (visibility 5 /8_mile or greater) FZDZ freezing drizzle . . . . . . . . . VCSH rain shower in the vicinity . . . . . . . . +SHRASNPL heavy rain showers, snow, . . ice pellets (intensity indicator refers to the predominant rain) 9. Sky Condition. The sky condition as reported in METAR represents a significant change from the way sky condition is currently reported. In METAR, sky condition is reported in the format: Amount/Height/(Type) or Indefinite Ceiling/Height AIM 2/14/08 7-1-63 Meteorology (a) Amount. The amount of sky cover is reported in eighths of sky cover, using the contractions: SKC clear (no clouds) . . . . . . . . . FEW >0 to 2 /8 . . . . . . . . SCT scattered (3 /8s to 4 /8s of . . . . . . . . . clouds) BKN broken (5 /8s to 7 /8s of clouds) . . . . . . . . . OVC overcast (8 /8s clouds) . . . . . . . . . CB Cumulonimbus when present . . . . . . . . . . TCU Towering cumulus when . . . . . . . . . present NOTE1. “SKC” will be reported at manual stations. “CLR” will be used at automated stations when no clouds below 12,000 feet are reported. 2. A ceiling layer is not designated in the METAR code. For aviation purposes, the ceiling is the lowest broken or overcast layer, or vertical visibility into an obscuration. Also there is no provision for reporting thin layers in the METAR code. When clouds are thin, that layer shall be reported as if it were opaque. (b) Height. Cloud bases are reported with three digits in hundreds of feet. (Clouds above 12,000_feet cannot be reported by an automated station). (c) (Type). If Towering Cumulus Clouds (TCU) or Cumulonimbus Clouds (CB) are present, they are reported after the height which represents their base. EXAMPLE(Reported as) SCT025TCU BKN080 BKN250 (spoken as) “TWO THOUSAND FIVE HUNDRED SCATTERED TOWERING CUMULUS, CEILING EIGHT THOUSAND BROKEN, TWO FIVE THOUSAND BROKEN.” (Reported as) SCT008 OVC012CB (spoken as) “EIGHT HUNDRED SCATTERED CEILING ONE THOUSAND TWO HUNDRED OVERCAST CUMULONIMBUS CLOUDS.” (d) Vertical Visibility (indefinite ceiling height). The height into an indefinite ceiling is preceded by “VV” and followed by three digits indicating the vertical visibility in hundreds of feet. This layer indicates total obscuration. EXAMPLE1 /8 SM FG VV006 - visibility one eighth, fog, indefinite ceiling six hundred. (e) Obscurations are reported when the sky is partially obscured by a ground-based phenomena by indicating the amount of obscuration as FEW, SCT, BKN followed by three zeros (000). In remarks, the obscuring phenomenon precedes the amount of obscuration and three zeros. EXAMPLE- BKN000 (in body) “sky partially obscured” . . . . . . . . FU BKN000 (in remarks) “smoke obscuring five- . . . to seven-eighths of the sky” (f) When sky conditions include a layer aloft, other than clouds, such as smoke or haze the type of phenomena, sky cover and height are shown in remarks. EXAMPLE- BKN020 (in body) “ceiling two thousand . . . . . . . . broken” RMK FU BKN020 “broken layer of smoke . . . . . . . . aloft, based at two thousand” (g) Variable ceiling. When a ceiling is below three thousand and is variable, the remark “CIG” will be shown followed with the lowest and highest ceiling heights separated by a “V.” EXAMPLE- CIG 005V010 “ceiling variable . . . . . . . . . . . . between five hundred and one thousand” (h) Second site sensor. When an automated station uses meteorological discontinuity sensors, remarks will be shown to identify site specific sky conditions which differ and are lower than conditions reported in the body. EXAMPLE- CIG 020 RY11 “ceiling two thousand at . . . . . . . . . . . runway one one” (i) Variable cloud layer. When a layer is varying in sky cover, remarks will show the variability range. If there is more than one cloud layer, the variable layer will be identified by including the layer height. EXAMPLE- SCT V BKN “scattered layer variable to . . . . . . . . . . . . . broken” BKN025 V OVC “broken layer at . . . . . . . . . two thousand five hundred variable to overcast” AIM 2/14/08 7-1-64 Meteorology (j) Significant clouds. When significant clouds are observed, they are shown in remarks, along with the specified information as shown below: (1) Cumulonimbus (CB), or Cumulonim- bus Mammatus (CBMAM), distance (if known), direction from the station, and direction of movement, if known. If the clouds are beyond 10_miles from the airport, DSNT will indicate distance. EXAMPLE- CB W MOV E “cumulonimbus west moving . . . . . . . east” CBMAM DSNT S “cumulonimbus mammatus . . . . distant south” (2) Towering Cumulus (TCU), location, (if known), or direction from the station. EXAMPLE- TCU OHD “towering cumulus overhead” . . . . . . . . . TCU W “towering cumulus west” . . . . . . . . . . . . (3) Altocumulus Castellanus (ACC), Stra- tocumulus Standing Lenticular (SCSL), Altocumulus Standing Lenticular (ACSL), Cirrocu- mulus Standing Lenticular (CCSL) or rotor clouds, describing the clouds (if needed) and the direction from the station. EXAMPLE- ACC W “altocumulus castellanus west” . . . . . . . . . . . . . ACSL SW-S “standing lenticular . . . . . . . . . altocumulus southwest through south” APRNT ROTOR CLD S “apparent rotor cloud south” CCSL OVR MT E “standing lenticular . . . . . cirrocumulus over the mountains east” 10. Temperature/Dew Point. Temperature and dew point are reported in two, two-digit groups in degrees Celsius, separated by a solidus (“/”). Temperatures below zero are prefixed with an “M.” If the temperature is available but the dew point is missing, the temperature is shown followed by a solidus. If the temperature is missing, the group is omitted from the report. EXAMPLE15/08 “temperature one five, . . . . . . . . . . . . . . dew point 8” 00/M02 “temperature zero, . . . . . . . . . . . . dew point minus 2” M05/ “temperature minus five, . . . . . . . . . . . . . . . dew point missing” 11. Altimeter. Altimeter settings are reported in a four-digit format in inches of mercury prefixed with an “A” to denote the units of pressure. EXAMPLE- A2995 - “Altimeter two niner niner five” 12. Remarks. Remarks will be included in all observations, when appropriate. The contraction “RMK” denotes the start of the remarks section of a METAR report. Except for precipitation, phenomena located within 5_statute miles of the point of observation will be reported as at the station. Phenomena between 5 and 10 statute miles will be reported in the vicinity, “VC.” Precipitation not occurring at the point of observation but within 10 statute miles is also reported as in the vicinity, “VC.” Phenomena beyond 10 statute miles will be shown as distant, “DSNT.” Distances are in statute miles except for automated lightning remarks which are in nautical miles. Movement of clouds or weather will be indicated by the direction toward which the phenomena is moving. (a) There are two categories of remarks: (1) Automated, manual, and plain language. (2) Additive and automated maintenance data. (b) Automated, Manual, and Plain Lan- guage. This group of remarks may be generated from either manual or automated weather reporting stations and generally elaborate on parameters reported in the body of the report. (Plain language remarks are only provided by manual stations). (1) Volcanic eruptions. (2) Tornado, Funnel Cloud, Waterspout. (3) Station Type (AO1 or AO2). (4) PK WND. (5) WSHFT (FROPA). (6) TWR VIS or SFC VIS. (7) VRB VIS. (8) Sector VIS. (9) VIS @ 2nd Site. (10) (freq) LTG (type) (loc). AIM 2/14/08 7-1-65

帅哥

Meteorology (11) Beginning/Ending of Precipitation/ TSTMS. (12) TSTM Location MVMT. (13) Hailstone Size (GR). (14) Virga. (15) VRB CIG (height). (16) Obscuration. (17) VRB Sky Condition. (18) Significant Cloud Types. (19) Ceiling Height 2nd Location. (20) PRESFR PRESRR. (21) Sea-Level Pressure. (22) ACFT Mishap (not transmitted). (23) NOSPECI. (24) SNINCR. (25) Other SIG Info. (c) Additive and Automated Maintenance Data. (1) Hourly Precipitation. (2) 3- and 6-Hour Precipitation Amount. (3) 24-Hour Precipitation. (4) Snow Depth on Ground. (5) Water Equivalent of Snow. (6) Cloud Type. (7) Duration of Sunshine. (8) Hourly Temperature/Dew Point (Tenths). (9) 6-Hour Maximum Temperature. (10) 6-Hour Minimum Temperature. (11) 24-Hour Maximum/Minimum Temperature. (12) Pressure Tendency. (13) Sensor Status. PWINO FZRANO TSNO RVRNO PNO VISNO Examples of METAR reports and explanation: METAR KBNA 281250Z 33018KT 290V360 1/2SM R31/2700FT SN BLSN FG VV008 00/M03 A2991 RMK RAE42SNB42 METAR aviation routine weather . . . . . . report KBNA Nashville, TN . . . . . . . . 281250Z date 28th , time 1250 UTC . . . . . . (no modifier) This is a manually generated . . report, due to the absence of “AUTO” and “AO1 or AO2” in remarks 33018KT wind three three zero at one . . . . . eight 290V360 wind variable between . . . . . . two nine zero and three six zero 1/2SM visibility one half . . . . . . . . R31/2700FT Runway three one RVR two . . . thousand seven hundred SN moderate snow . . . . . . . . . . . BLSN FG visibility obscured by . . . . . blowing snow and fog VV008 indefinite ceiling eight . . . . . . . hundred 00/M03 temperature zero, dew point . . . . . . . minus three A2991 altimeter two niner niner one . . . . . . . . RMK remarks . . . . . . . . RAE42 rain ended at four two . . . . . . . SNB42 snow began at four two . . . . . . . METAR KSFO 041453Z AUTO VRB02KT 3SM BR CLR 15/12 A3012 RMK AO2 METAR aviation routine weather . . . . . . report KSFO San Francisco, CA . . . . . . . . 041453Z date 4th , time 1453 UTC . . . . . . AUTO fully automated; no human . . . . . . . intervention VRB02KT wind variable at two . . . . 3SM visibility three . . . . . . . . . BR visibility obscured by mist . . . . . . . . . . CLR no clouds below one two . . . . . . . . . thousand 15/12 temperature one five, dew . . . . . . . . . point one two AIM 2/14/08 7-1-66 Meteorology A3012 altimeter three zero one two . . . . . . . . RMK remarks . . . . . . . . AO2 this automated station has a . . . . . . . . . weather discriminator (for precipitation) SPECI KCVG 152224Z 28024G36KT 3/4SM +TSRA BKN008 OVC020CB 28/23 A3000 RMK TSRAB24 TS W MOV E SPECI (nonroutine) aviation special . . . . . . . weather report KCVG Cincinnati, OH . . . . . . . 152228Z date 15th , time 2228 UTC . . . . . . (no modifier) This is a manually generated . . report due to the absence of “AUTO” and “AO1 or AO2” in remarks 28024G36KT wind two eight zero at . . two four gusts three six 3/4SM visibility three fourths . . . . . . . . +TSRA thunderstorms, heavy rain . . . . . . . BKN008 ceiling eight hundred broken OVC020CB two thousand overcast . . . cumulonimbus clouds 28/23 temperature two eight, . . . . . . . . . dew point two three A3000 altimeter three zero zero zero . . . . . . . . RMK remarks . . . . . . . . TSRAB24 thunderstorm and rain began . . . . . at two four TS W MOV E thunderstorm west moving east c. Aerodrome Forecast (TAF). A concise state- ment of the expected meteorological conditions at an airport during a specified period (usually 24 hours). TAFs use the same codes as METAR weather reports. They are scheduled four times daily for 24-hour periods beginning at 0000Z, 0600Z, 1200Z, and 1800Z. TAFs are issued in the following format: TYPE OF REPORT/ICAO STATION IDENTIFIER/ DATE AND TIME OF ORIGIN/VALID PERIOD DATE AND TIME/FORECAST METEOROLOG- ICAL CONDITIONS NOTE- The “/” above and in the following descriptions are for separation purposes in this publication and do not appear in the actual TAFs. TAF KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1 /2SM BR _____FM1600 16010KT P6SM SKC _____FM2300 20013G20KT 4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB BECMG 0608 21015KT P6SM NSW SCT040 TAF format observed in the above example: TAF = type of report KOKC = ICAO station identifier 051130Z = date and time of origin 051212 = valid period date and times 14008KT 5SM BR BKN030 = forecast meteorologi- cal conditions Explanation of TAF elements: 1. Type of Report. There are two types of TAF issuances, a routine forecast issuance (TAF) and an amended forecast (TAF AMD). An amended TAF is issued when the current TAF no longer adequately describes the on-going weather or the forecaster feels the TAF is not representative of the current or expected weather. Corrected (COR) or delayed (RTD) TAFs are identified only in the communica- tions header which precedes the actual forecasts. 2. ICAO Station Identifier. The TAF code uses ICAO 4-letter location identifiers as described in the METAR section. 3. Date and Time of Origin. This element is the date and time the forecast is actually prepared. The format is a two-digit date and four-digit time followed, without a space, by the letter “Z.” 4. Valid Period Date and Time. The UTC valid period of the forecast is a two-digit date followed by the two-digit beginning hour and two-digit ending hour. In the case of an amended forecast, or a forecast which is corrected or delayed, the valid period may be for less than 24 hours. Where an airport or terminal operates on a part-time basis (less than 24 hours/day), the TAFs issued for those locations will have the abbreviated statement “NIL AMD SKED AFT (closing time) Z” added to the end of the forecasts. For the TAFs issued while these locations are closed, the word “NIL” will appear in place of the forecast text. A delayed (RTD) forecast will then be issued for these locations after two complete observations are received. AIM 2/14/08 7-1-67 Meteorology 5. Forecast Meteorological Conditions. This is the body of the TAF. The basic format is: W I N D / V I S I B I L I T Y / W E AT H E R / S K Y CONDITION/OPTIONAL DATA (WIND SHEAR) The wind, visibility, and sky condition elements are always included in the initial time group of the forecast. Weather is included only if significant to aviation. If a significant, lasting change in any of the elements is expected during the valid period, a new time period with the changes is included. It should be noted that with the exception of a “FM” group the new time period will include only those elements which are expected to change, i.e., if a lowering of the visibility is expected but the wind is expected to remain the same, the new time period reflecting the lower visibility would not include a forecast wind. The forecast wind would remain the same as in the previous time period. Any temporary conditions expected during a specific time period are included with that time period. The following describes the elements in the above format. (a) Wind. This five (or six) digit group includes the expected wind direction (first 3 digits) and speed (last 2 digits or 3 digits if 100 knots or greater). The contraction “KT” follows to denote the units of wind speed. Wind gusts are noted by the letter “G” appended to the wind speed followed by the highest expected gust. A variable wind direction is noted by “VRB” where the three digit direction usually appears. A calm wind (3 knots or less) is forecast as “00000KT.” EXAMPLE18010KT wind one eight zero at one zero (wind is . . . . . blowing from 180). 35012G20KT wind three five zero at one two gust two . . zero. (b) Visibility. The expected prevailing visi- bility up to and including 6 miles is forecast in statute miles, including fractions of miles, followed by “SM” to note the units of measure. Expected visibilities greater than 6 miles are forecast as P6SM (plus six_statute miles). EXAMPLE1 /2SM - visibility one-half 4SM - visibility four P6SM - visibility more than six (c) Weather Phenomena. The expected weather phenomena is coded in TAF reports using the same format, qualifiers, and phenomena contractions as METAR reports (except UP). Obscurations to vision will be forecast whenever the prevailing visibility is forecast to be 6 statute miles or less. If no significant weather is expected to occur during a specific time period in the forecast, the weather phenomena group is omitted for that time period. If, after a time period in which significant weather phenomena has been forecast, a change to a forecast of no significant weather phenomena occurs, the contraction NSW (No Significant Weather) will appear as the weather group in the new time period. (NSW is included only in BECMG or TEMPO groups). NOTE- It is very important that pilots understand that NSW only refers to weather phenomena, i.e., rain, snow, drizzle, etc. Omitted conditions, such as sky conditions, visibility, winds, etc., are carried over from the previous time group. (d) Sky Condition. TAF sky condition forecasts use the METAR format described in the METAR section. Cumulonimbus clouds (CB) are the only cloud type forecast in TAFs. When clear skies are forecast, the contraction “SKC” will always be used. The contraction “CLR” is never used in the TAF. When the sky is obscured due to a surface-based phenomenon, vertical visibility (VV) into the obscuration is forecast. The format for vertical visibility is “VV” followed by a three-digit height in hundreds of feet. NOTE- As in METAR, ceiling layers are not designated in the TAF code. For aviation purposes, the ceiling is the lowest broken or overcast layer or vertical visibility into a complete obscuration. SKC “sky clear” . . . . . . . . . . . . . . SCT005 BKN025CB “five hundred scattered, ceiling two thousand five hundred broken cumulonimbus clouds” VV008 “indefinite ceiling . . . . . . . . . . . . eight hundred” AIM 2/14/08 7-1-68 Meteorology (e) Optional Data (Wind Shear). Wind shear is the forecast of nonconvective low level winds (up to 2,000 feet). The forecast includes the letters “WS” followed by the height of the wind shear, the wind direction and wind speed at the indicated height and the ending letters “KT” (knots). Height is given in hundreds of feet (AGL) up to and including 2,000_feet. Wind shear is encoded with the contraction “WS,” followed by a three-digit height, slant character “/,” and winds at the height indicated in the same format as surface winds. The wind shear element is omitted if not expected to occur. WS010/18040KT - “LOW LEVEL WIND SHEAR AT ONE THOUSAND, WIND ONE EIGHT ZERO AT FOUR ZERO” d. Probability Forecast. The probability or chance of thunderstorms or other precipitation events occurring, along with associated weather conditions (wind, visibility, and sky conditions). The PROB30 group is used when the occurrence of thunderstorms or precipitation is 30-39% and the PROB40 group is used when the occurrence of thunderstorms or precipitation is 40-49%. This is followed by a four-digit group giving the beginning hour and ending hour of the time period during which the thunderstorms or precipitation are expected. NOTE- Neither PROB30 nor PROB40 will be shown during the first six hours of a forecast. EXAMPLE- PROB40 2102 1 /2SM +TSRA “chance between . . . . 2100Z and 0200Z of visibility one-half statute mile in thunderstorms and heavy rain.” PROB30 1014 1SM RASN “chance between . . . . . . 1000Z and 1400Z of visibility one statute mile in mixed rain and snow.” e. Forecast Change Indicators. The following change indicators are used when either a rapid, gradual, or temporary change is expected in some or all of the forecast meteorological conditions. Each change indicator marks a time group within the TAF report. 1. From (FM) group. The FM group is used when a rapid change, usually occurring in less than one hour, in prevailing conditions is expected. Typically, a rapid change of prevailing conditions to more or less a completely new set of prevailing conditions is associated with a synoptic feature passing through the terminal area (cold or warm frontal passage). Appended to the “FM” indicator is the four-digit hour and minute the change is expected to begin and continues until the next change group or until the end of the current forecast. A “FM” group will mark the beginning of a new line in a TAF report (indented 5 spaces). Each “FM” group contains all the required elements-wind, visibility, weather, and sky condition. Weather will be omitted in “FM” groups when it is not significant to aviation. FM groups will not include the contraction NSW. EXAMPLE- FM0100 14010KT P6SM SKC - “after 0100Z, wind one_four zero at one zero, visibility more than six, sky clear.” 2. Becoming (BECMG) group. The BECMG group is used when a gradual change in conditions is expected over a longer time period, usually two hours. The time period when the change is expected is a four-digit group with the beginning hour and ending hour of the change period which follows the BECMG indicator. The gradual change will occur at an unspecified time within this time period. Only the changing forecast meteorological conditions are included in BECMG groups. The omitted conditions are carried over from the previous time group. EXAMPLE- OVC012 BECMG 1416 BKN020 - “ceiling one thousand two hundred overcast. Then a gradual change to ceiling two thousand broken between 1400Z and 1600Z.” 3. Temporary (TEMPO) group. The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period. The TEMPO indicator is followed by a four-digit group giving the beginning hour and ending hour of the time period during which the temporary conditions are expected. Only the changing forecast meteorological conditions are included in TEMPO groups. The omitted conditions are carried over from the previous time group. AIM 2/14/08 7-1-69 Meteorology EXAMPLE1. SCT030 TEMPO 1923 BKN030 - “three thousand scattered with occasional ceilings three thousand broken between 1900Z and 2300Z.” 2. 4SM HZ TEMPO 0006 2SM BR HZ - “visibility four in haze with occasional visibility two in mist and haze between 0000Z and 0600Z.” AIM 2/14/08 7-2-1 Altimeter Setting Procedures Section 2. Altimeter Setting Procedures 7-2-1. General a. The accuracy of aircraft altimeters is subject to the following factors: 1. Nonstandard temperatures of the atmosphere. 2. Nonstandard atmospheric pressure. 3. Aircraft static pressure systems (position error); and 4. Instrument error. b. EXTREME CAUTION SHOULD BE EXER- CISED WHEN FLYING IN PROXIMITY TO OBSTRUCTIONS OR TERRAIN IN LOW TEM- PERATURES AND PRESSURES. This is especially true in extremely cold temperatures that cause a large differential between the Standard Day temperature and actual temperature. This circumstance can cause serious errors that result in the aircraft being significantly lower than the indicated altitude. NOTE- Standard temperature at sea level is 15 degrees Celsius (59_degrees Fahrenheit). The temperature gradient from sea level is minus 2 degrees Celsius (3.6 degrees Fahrenheit) per 1,000 feet. Pilots should apply corrections for static pressure systems and/or instruments, if appreciable errors exist. c. The adoption of a standard altimeter setting at the higher altitudes eliminates station barometer errors, some altimeter instrument errors, and errors caused by altimeter settings derived from different geographical sources. 7-2-2. Procedures The cruising altitude or flight level of aircraft shall be maintained by reference to an altimeter which shall be set, when operating: a. Below 18,000 feet MSL. 1. When the barometric pressure is 31.00_inches Hg. or less. To the current reported altimeter setting of a station along the route and within 100 NM of the aircraft, or if there is no station within this area, the current reported altimeter setting of an appropriate available station. When an aircraft is en route on an instrument flight plan, air traffic controllers will furnish this information to the pilot at least once while the aircraft is in the controllers area of jurisdiction. In the case of an aircraft not equipped with a radio, set to the elevation of the departure airport or use an appropriate altimeter setting available prior to departure. 2. When the barometric pressure exceeds 31.00 inches Hg. The following procedures will be placed in effect by NOTAM defining the geographic area affected: (a) For all aircraft. Set 31.00 inches for en route operations below 18,000 feet MSL. Maintain this setting until beyond the affected area or until reaching final approach segment. At the beginning of the final approach segment, the current altimeter setting will be set, if possible. If not possible, 31.00_inches will remain set throughout the ap- proach. Aircraft on departure or missed approach will set 31.00 inches prior to reaching any mandatory/ crossing altitude or 1,500 feet AGL, whichever is lower. (Air traffic control will issue actual altimeter settings and advise pilots to set 31.00 inches in their altimeters for en route operations below 18,000 feet MSL in affected areas.) (b) During preflight, barometric altimeters shall be checked for normal operation to the extent possible. (c) For aircraft with the capability of setting the current altimeter setting and operating into airports with the capability of measuring the current altimeter setting, no additional restrictions apply. (d) For aircraft operating VFR, there are no additional restrictions, however, extra diligence in flight planning and in operating in these conditions is essential. (e) Airports unable to accurately measure barometric pressures above 31.00 inches of Hg. will report the barometric pressure as “missing” or “in excess of 31.00 inches of Hg.” Flight operations to and from those airports are restricted to VFR weather conditions. AIM 2/14/08

帅哥

7-2-2 Altimeter Setting Procedures (f) For aircraft operating IFR and unable to set the current altimeter setting, the following restric- tions apply: (1) To determine the suitability of depar- ture alternate airports, destination airports, and destination alternate airports, increase ceiling requirements by 100 feet and visibility requirements by 1 /4 statute mile for each 1 /10 of an inch of Hg., or any portion thereof, over 31.00 inches. These adjusted values are then applied in accordance with the requirements of the applicable operating regulations and operations specifications. EXAMPLE- Destination altimeter is 31.28 inches, ILS DH 250 feet (200-1 /2). When flight planning, add 300-3 /4 to the weather requirements which would become 500-11 /4. (2) On approach, 31.00 inches will remain set. Decision height (DH) or minimum descent altitude shall be deemed to have been reached when the published altitude is displayed on the altimeter. NOTE- Although visibility is normally the limiting factor on an approach, pilots should be aware that when reaching DH the aircraft will be higher than indicated. Using the example above the aircraft would be approximately 300_feet higher. (3) These restrictions do not apply to authorized Category II and III ILS operations nor do they apply to certificate holders using approved QFE altimetry systems. (g) The FAA Regional Flight Standards Division Manager of the affected area is authorized to approve temporary waivers to permit emergency resupply or emergency medical service operation. b. At or above 18,000 feet MSL. To 29.92_inch- es of mercury (standard setting). The lowest usable flight level is determined by the atmospheric pressure in the area of operation as shown in TBL 7-2-1. TBL 7-2-1 Lowest Usable Flight Level Altimeter Setting (Current Reported) Lowest Usable Flight Level 29.92 or higher 180 29.91 to 29.42 185 29.41 to 28.92 190 28.91 to 28.42 195 28.41 to 27.92 200 c. Where the minimum altitude, as prescribed in 14_CFR Section 91.159 and 14_CFR Section 91.177, is above 18,000 feet MSL, the lowest usable flight level shall be the flight level equivalent of the minimum altitude plus the number of feet specified in TBL 7-2-2. TBL 7-2-2 Lowest Flight Level Correction Factor Altimeter Setting Correction Factor 29.92 or higher none 29.91 to 29.42 500 feet 29.41 to 28.92 1000 feet 28.91 to 28.42 1500 feet 28.41 to 27.92 2000 feet 27.91 to 27.42 2500 feet EXAMPLE- The minimum safe altitude of a route is 19,000 feet MSL and the altimeter setting is reported between 29.92 and 29.42 inches of mercury, the lowest usable flight level will be 195, which is the flight level equivalent of 19,500 feet MSL (minimum altitude plus 500 feet). AIM 2/14/08 7-2-3 Altimeter Setting Procedures 7-2-3. Altimeter Errors a. Most pressure altimeters are subject to mechanical, elastic, temperature, and installation errors. (Detailed information regarding the use of pressure altimeters is found in the Instrument Flying Handbook, Chapter IV.) Although manufacturing and installation specifications, as well as the periodic test and inspections required by regulations (14 CFR Part 43, Appendix E), act to reduce these errors, any scale error may be observed in the following manner: 1. Set the current reported altimeter setting on the altimeter setting scale. 2. Altimeter should now read field elevation if you are located on the same reference level used to establish the altimeter setting. 3. Note the variation between the known field elevation and the altimeter indication. If this variation is in the order of plus or minus 75 feet, the accuracy of the altimeter is questionable and the problem should be referred to an appropriately rated repair station for evaluation and possible correction. b. Once in flight, it is very important to obtain frequently current altimeter settings en route. If you do not reset your altimeter when flying from an area of high pressure into an area of low pressure, your aircraft will be closer to the surface than your altimeter indicates. An inch error in the altimeter setting equals 1,000 feet of altitude. To quote an old saying: “GOING FROM A HIGH TO A LOW, LOOK OUT BELOW.” c. Temperature also has an effect on the accuracy of altimeters and your altitude. The crucial values to consider are standard temperature versus the ambient (at altitude) temperature. It is this “difference” that causes the error in indicated altitude. When the air is warmer than standard, you are higher than your altimeter indicates. Subsequently, when the air is colder than standard you are lower than indicated. It is the magnitude of this “difference” that determines the magnitude of the error. When flying into a cooler air mass while maintaining a constant indicated altitude, you are losing true altitude. However, flying into a cooler air mass does not necessarily mean you will be lower than indicated if the difference is still on the plus side. For example, while flying at 10,000 feet (where STANDARD temperature is -5 degrees Celsius (C)), the outside air temperature cools from +5 degrees C to 0 degrees C, the temperature error will nevertheless cause the aircraft to be HIGHER than indicated. It is the extreme “cold” difference that normally would be of concern to the pilot. Also, when flying in cold conditions over mountainous country, the pilot should exercise caution in flight planning both in regard to route and altitude to ensure adequate en route and terminal area terrain clearance. d. TBL 7-2-3, derived from ICAO formulas, indicates how much error can exist when the temperature is extremely cold. To use the table, find the reported temperature in the left column, then read across the top row to locate the height above the airport/reporting station (i.e., subtract the airport/ reporting elevation from the intended flight altitude). The intersection of the column and row is how much lower the aircraft may actually be as a result of the possible cold temperature induced error. e. The possible result of the above example should be obvious, particularly if operating at the minimum altitude or when conducting an instrument approach. When operating in extreme cold temperatures, pilots may wish to compensate for the reduction in terrain clearance by adding a cold temperature correction. AIM 2/14/08 7-2-4 Altimeter Setting Procedures TBL 7-2-3 ICAO Cold Temperature Error Table Reported Temp _C Height Above Airport in Feet 200 300 400 500 600 700 800 900 1000 1500 2000 3000 4000 5000 +10 10 10 10 10 20 20 20 20 20 30 40 60 80 90 0 20 20 30 30 40 40 50 50 60 90 120 170 230 280 -10 20 30 40 50 60 70 80 90 100 150 200 290 390 490 -20 30 50 60 70 90 100 120 130 140 210 280 420 570 710 -30 40 60 80 100 120 140 150 170 190 280 380 570 760 950 -40 50 80 100 120 150 170 190 220 240 360 480 720 970 1210 -50 60 90 120 150 180 210 240 270 300 450 590 890 1190 1500 EXAMPLE- Temperature-10 degrees Celsius, and the aircraft altitude is 1,000 feet above the airport elevation. The chart shows that the reported current altimeter setting may place the aircraft as much as 100 feet below the altitude indicated by the altimeter. 7-2-4. High Barometric Pressure a. Cold, dry air masses may produce barometric pressures in excess of 31.00 inches of Mercury, and many altimeters do not have an accurate means of being adjusted for settings of these levels. When the altimeter cannot be set to the higher pressure setting, the aircraft actual altitude will be higher than the altimeter indicates. REFERENCE- AIM, Paragraph 7-2-3, Altimeter Errors. b. When the barometric pressure exceeds 31.00_inches, air traffic controllers will issue the actual altimeter setting, and: 1. En Route/Arrivals. Advise pilots to remain set on 31.00 inches until reaching the final approach segment. 2. Departures. Advise pilots to set 31.00_inch- es prior to reaching any mandatory/crossing altitude or 1,500 feet, whichever is lower. c. The altimeter error caused by the high pressure will be in the opposite direction to the error caused by the cold temperature. 7-2-5. Low Barometric Pressure When abnormally low barometric pressure condi- tions occur (below 28.00), flight operations by aircraft unable to set the actual altimeter setting are not recommended. NOTE- The true altitude of the aircraft is lower than the indicated altitude if the pilot is unable to set the actual altimeter setting. AIM 2/14/08 7-3-1 Wake Turbulence Section 3. Wake Turbulence 7-3-1. General a. Every aircraft generates a wake while in flight. Initially, when pilots encountered this wake in flight, the disturbance was attributed to “prop wash.” It is known, however, that this disturbance is caused by a pair of counter-rotating vortices trailing from the wing tips. The vortices from larger aircraft pose problems to encountering aircraft. For instance, the wake of these aircraft can impose rolling moments exceeding the roll-control authority of the encounter- ing aircraft. Further, turbulence generated within the vortices can damage aircraft components and equipment if encountered at close range. The pilot must learn to envision the location of the vortex wake generated by larger (transport category) aircraft and adjust the flight path accordingly. b. During ground operations and during takeoff, jet engine blast (thrust stream turbulence) can cause damage and upsets if encountered at close range. Exhaust velocity versus distance studies at various thrust levels have shown a need for light aircraft to maintain an adequate separation behind large turbojet aircraft. Pilots of larger aircraft should be particularly careful to consider the effects of their “jet blast” on other aircraft, vehicles, and maintenance equipment during ground operations. 7-3-2. Vortex Generation Lift is generated by the creation of a pressure differential over the wing surface. The lowest pressure occurs over the upper wing surface and the highest pressure under the wing. This pressure differential triggers the roll up of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wing tips. After the roll up is completed, the wake consists of two counter-rotating cylindrical vortices. (See FIG 7-3-1.) Most of the energy is within a few feet of the center of each vortex, but pilots should avoid a region within about 100 feet of the vortex core. FIG 7-3-1 Wake Vortex Generation 7-3-3. Vortex Strength a. The strength of the vortex is governed by the weight, speed, and shape of the wing of the generating aircraft. The vortex characteristics of any given aircraft can also be changed by extension of flaps or other wing configuring devices as well as by change in speed. However, as the basic factor is weight, the vortex strength increases proportionately. Peak vortex tangential speeds exceeding 300 feet per second have been recorded. The greatest vortex strength occurs when the generating aircraft is HEAVY, CLEAN, and SLOW. b. Induced Roll 1. In rare instances a wake encounter could cause inflight structural damage of catastrophic proportions. However, the usual hazard is associated with induced rolling moments which can exceed the roll-control authority of the encountering aircraft. In flight experiments, aircraft have been intentionally flown directly up trailing vortex cores of larger aircraft. It was shown that the capability of an aircraft to counteract the roll imposed by the wake vortex primarily depends on the wingspan and counter- control responsiveness of the encountering aircraft. AIM 2/14/08 7-3-2 Wake Turbulence 2. Counter control is usually effective and induced roll minimal in cases where the wingspan and ailerons of the encountering aircraft extend beyond the rotational flow field of the vortex. It is more difficult for aircraft with short wingspan (relative to the generating aircraft) to counter the imposed roll induced by vortex flow. Pilots of short span aircraft, even of the high performance type, must be especially alert to vortex encounters. (See FIG 7-3-2.) FIG 7-3-2 Wake Encounter Counter Control COUNTER CONTROL 3. The wake of larger aircraft requires the respect of all pilots. 7-3-4. Vortex Behavior a. Trailing vortices have certain behavioral characteristics which can help a pilot visualize the wake location and thereby take avoidance precau- tions. 1. Vortices are generated from the moment aircraft leave the ground, since trailing vortices are a by-product of wing lift. Prior to takeoff or touchdown pilots should note the rotation or touchdown point of the preceding aircraft. (See FIG 7-3-4.) 2. The vortex circulation is outward, upward and around the wing tips when viewed from either ahead or behind the aircraft. Tests with large aircraft have shown that the vortices remain spaced a bit less than a wingspan apart, drifting with the wind, at altitudes greater than a wingspan from the ground. In view of this, if persistent vortex turbulence is encountered, a slight change of altitude and lateral position (preferably upwind) will provide a flight path clear of the turbulence.

帅哥

3. Flight tests have shown that the vortices from larger (transport category) aircraft sink at a rate of several hundred feet per minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft. Atmospheric turbulence hastens breakup. Pilots should fly at or above the preceding aircraft's flight path, altering course as necessary to avoid the area behind and below the generating aircraft. (See FIG 7-3-3.) However, vertical separation of 1,000 feet may be considered safe. 4. When the vortices of larger aircraft sink close to the ground (within 100 to 200 feet), they tend to move laterally over the ground at a speed of 2 or 3_knots. (See FIG 7-3-5.) FIG 7-3-3 Wake Ends/Wake Begins Touchdown Rotation Wake Ends Wake Begins AIM 2/14/08 7-3-3 Wake Turbulence FIG 7-3-4 Vortex Flow Field AVOID Nominally 500-1000 Ft. Sink Rate Min. Several Hundred Ft.,/FIG 7-3-5 Vortex Movement Near Ground - No Wind No Wind 3K 3K FIG 7-3-6 Vortex Movement Near Ground - with Cross Winds 6K (3K + 3K) 3K Wind 0 (3K - 3K) AIM 2/14/08 7-3-4 Wake Turbulence 5. There is a small segment of the aviation community that have become convinced that wake vortices may “bounce” up to twice their nominal steady state height. With a 200-foot span aircraft, the “bounce” height could reach approximately 200 feet AGL. This conviction is based on a single unsubstantiated report of an apparent coherent vortical flow that was seen in the volume scan of a research sensor. No one can say what conditions cause vortex bouncing, how high they bounce, at what angle they bounce, or how many times a vortex may bounce. On the other hand, no one can say for certain that vortices never “bounce.” Test data have shown that vortices can rise with the air mass in which they are embedded. Wind shear, particularly, can cause vortex flow field “tilting.” Also, ambient thermal lifting and orographic effects (rising terrain or tree lines) can cause a vortex flow field to rise. Notwithstanding the foregoing, pilots are reminded that they should be alert at all times for possible wake vortex encounters when conducting approach and landing operations. The pilot has the ultimate responsibility for ensuring appropriate separations and positioning of the aircraft in the terminal area to avoid the wake turbulence created by a preceding aircraft.

帅哥

b. A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex. Thus a light wind with a cross runway component of 1 to 5 knots could result in the upwind vortex remaining in the touchdown zone for a period of time and hasten the drift of the downwind vortex toward another runway. (See FIG 7-3-6.) Similarly, a tailwind condition can move the vortices of the preceding aircraft forward into the touchdown zone. THE LIGHT QUARTERING TAILWIND REQUIRES MAXIMUM CAUTION. Pilots should be alert to large aircraft upwind from their approach and takeoff flight paths. (See FIG 7-3-7.) FIG 7-3-7 Vortex Movement in Ground Effect - Tailwind Light Quartering Tailwind x Tail Wind Touchdown Point AIM 2/14/08 7-3-5 Wake Turbulence 7-3-5. Operations Problem Areas a. A wake encounter can be catastrophic. In 1972 at Fort Worth a DC-9 got too close to a DC-10 (two_miles back), rolled, caught a wingtip, and cartwheeled coming to rest in an inverted position on the runway. All aboard were killed. Serious and even fatal GA accidents induced by wake vortices are not uncommon. However, a wake encounter is not necessarily hazardous. It can be one or more jolts with varying severity depending upon the direction of the encounter, weight of the generating aircraft, size of the encountering aircraft, distance from the generat- ing aircraft, and point of vortex encounter. The probability of induced roll increases when the encountering aircraft's heading is generally aligned with the flight path of the generating aircraft. b. AVOID THE AREA BELOW AND BEHIND THE GENERATING AIRCRAFT, ESPECIALLY AT LOW ALTITUDE WHERE EVEN A MOMENTARY WAKE ENCOUNTER COULD BE HAZARDOUS. This is not easy to do. Some accidents have occurred even though the pilot of the trailing aircraft had carefully noted that the aircraft in front was at a considerably lower altitude. Unfortu- nately, this does not ensure that the flight path of the lead aircraft will be below that of the trailing aircraft. c. Pilots should be particularly alert in calm wind conditions and situations where the vortices could: 1. Remain in the touchdown area. 2. Drift from aircraft operating on a nearby runway. 3. Sink into the takeoff or landing path from a crossing runway. 4. Sink into the traffic pattern from other airport operations. 5. Sink into the flight path of VFR aircraft operating on the hemispheric altitude 500 feet below. d. Pilots of all aircraft should visualize the location of the vortex trail behind larger aircraft and use proper vortex avoidance procedures to achieve safe operation. It is equally important that pilots of larger aircraft plan or adjust their flight paths to minimize vortex exposure to other aircraft.

帅哥

7-3-6. Vortex Avoidance Procedures a. Under certain conditions, airport traffic control- lers apply procedures for separating IFR aircraft. If a pilot accepts a clearance to visually follow a preceding aircraft, the pilot accepts responsibility for separation and wake turbulence avoidance. The controllers will also provide to VFR aircraft, with whom they are in communication and which in the tower's opinion may be adversely affected by wake turbulence from a larger aircraft, the position, altitude and direction of flight of larger aircraft followed by the phrase “CAUTION - WAKE TURBULENCE.” After issuing the caution for wake turbulence, the airport traffic controllers generally do not provide additional information to the following aircraft unless the airport traffic controllers know the following aircraft is overtaking the preceding aircraft. WHETHER OR NOT A WARNING OR INFORMATION HAS BEEN GIVEN, HOWEVER, THE PILOT IS EXPECTED TO ADJUST AIR- CRAFT OPERATIONS AND FLIGHT PATH AS NECESSARY TO PRECLUDE SERIOUS WAKE ENCOUNTERS. When any doubt exists about maintaining safe separation distances between aircraft during approaches, pilots should ask the control tower for updates on separation distance and aircraft groundspeed.

帅哥

b. The following vortex avoidance procedures are recommended for the various situations: 1. Landing behind a larger aircraft- same runway. Stay at or above the larger aircraft's final approach flight path-note its touchdown point-land beyond it. 2. Landing behind a larger aircraft- when parallel runway is closer than 2,500 feet. Consider possible drift to your runway. Stay at or above the larger aircraft's final approach flight path- note its touchdown point.

帅哥

3. Landing behind a larger aircraft- crossing runway. Cross above the larger aircraft's flight path. 4. Landing behind a departing larger air- craft- same runway. Note the larger aircraft's rotation point- land well prior to rotation point. 5. Landing behind a departing larger air- craft- crossing runway. Note the larger aircraft's rotation point- if past the intersection- continue the approach- land prior to the intersection. If larger aircraft rotates prior to the intersection, avoid flight AIM 2/14/08 7-3-6 Wake Turbulence below the larger aircraft's flight path. Abandon the approach unless a landing is ensured well before reaching the intersection. 6. Departing behind a larger aircraft. Note the larger aircraft's rotation point and rotate prior to the larger aircraft's rotation point. Continue climbing above the larger aircraft's climb path until turning clear of the larger aircraft's wake. Avoid subsequent headings which will cross below and behind a larger aircraft. Be alert for any critical takeoff situation which could lead to a vortex encounter.

帅哥

7. Intersection takeoffs- same runway. Be alert to adjacent larger aircraft operations, particular- ly upwind of your runway. If intersection takeoff clearance is received, avoid subsequent heading which will cross below a larger aircraft's path. 8. Departing or landing after a larger aircraft executing a low approach, missed approach, or touch-and-go landing. Because vortices settle and move laterally near the ground, the vortex hazard may exist along the runway and in your flight path after a larger aircraft has executed a low approach, missed approach, or a touch-and-go landing, particular in light quartering wind condi- tions. You should ensure that an interval of at least 2_minutes has elapsed before your takeoff or landing. 9. En route VFR (thousand-foot altitude plus 500 feet). Avoid flight below and behind a large aircraft's path. If a larger aircraft is observed above on the same track (meeting or overtaking) adjust your position laterally, preferably upwind.