Par 9 Page 13 weight and configuration of the generating aircraft, size of the encountering aircraft, distance from the generating aircraft, and point of vortex encounter. The probability of induced roll increases when the encountering aircraft’s heading is generally aligned or parallel with the flightpath of the generating aircraft. Avoid the area below and behind the generating aircraft, especially at low altitude where even a momentary wake encounter could be hazardous. Pilots should be particularly alert in calm wind conditions and maneuvering situations in the vicinity of the airport where the vortices could:
(1) Remain in the touchdown area,
(2) Drift from aircraft operating on a nearby runway,
(3) Sink into takeoff or landing path from a crossing runway, or
(4) Sink into the traffic patterns from other airport operations.
b. Visualize the Vortex Trail. 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 also important that pilots of larger aircraft fly on the GS, not above it, whenever possible, to minimize vortex exposure to other aircraft.
c. Control Inputs. There is a history of wake vortex encounter incidents in which pilot inputs exacerbated the unusual attitude situation caused by the wake vortex encounter. Upsets caused by wake vortex encounters may involve rapid roll reversals as the aircraft transitions across the wake. Pilots should exercise caution with pilot control inputs, especially avoiding abrupt reversal of aileron and rudder control inputs. If altitude and conditions permit, it may be better to allow the aircraft to transition through the wake and then recover from any resultant unusual attitude, rather than aggressively trying to control the aircraft during the wake encounter.
If the autopilot is engaged and remains engaged, it may be better to allow the autopilot to recover from the wake vortex encounter rather than disconnecting the autopilot and using manual control inputs. However, be prepared to assume manual control of the aircraft if the autopilot disengages.
d. Rudder Inputs. Prior experience or training that emphasizes use of rudder input as a means to maneuver in roll may not apply to all aircraft operations. Using the rudder to counter roll rate during a roll upset may lead to an undesirable aircraft response. Large, aggressive control reversals can lead to loads that can exceed the structural design limits. Refer to your specific Aircraft Flight Manual (AFM) guidance.
10. HELICOPTERS. A hovering helicopter generates a downwash from its main rotor(s). Pilots should avoid taxiing or flying within a distance of three rotor diameters of a helicopter hovering or in a slow hover taxi, as the downwash can contain high wind speeds. However, in forward flight, this energy is transformed into a pair of strong, high-speed, trailing vortices similar to wing-tip vortices of larger fixed-wing aircraft. Pilots should avoid helicopter vortices since helicopter forward flight airspeeds are often very low, which generate strong wake turbulence (see Figure 17, Helicopter Vortices).
FIGURE 17. HELICOPTER VORTICES Slow Hover Taxi or Stationary Hover:
Avoid Operations Within Distances of 3 Times Rotor Diameter Avoid Avoid Avoid Avoid Avoid Avoid Avoid Avoid Forward Flight, Landing and Departing Helicopters:
Small Aircraft, Use Caution Behind/Crossing Behind
11. PILOT RESPONSIBILITY.
a. Vortex Avoidance. Government and industry groups are making concerted efforts to minimize or eliminate the hazards of trailing vortices. However, the pilot must exercise the flight awareness necessary to ensure vortex avoidance during visual meteorological conditions (VMC).
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Par 11 Page 15 The pilot should exercise vortex visualization and avoidance procedures using the same degree of awareness as in collision avoidance.
b. ATC Instructions. Pilots should remember that, in operations conducted behind all aircraft, acceptance of instructions from ATC in the following situations is an acknowledgment that they will ensure safe takeoff and landing intervals, and accept the responsibility for providing wake turbulence separation:
(1) Traffic information,
(2) Instructions to follow an aircraft, and
(3) Acceptance of a visual approach clearance.
c. Identify Heavy or Super Aircraft. For operations conducted behind Heavy or Super aircraft, ATC will specify the word “Heavy” or “Super” when this information is known. Pilots of these aircraft should always use the appropriately designated weight identifying term in radio communication within the terminal area.
d. Flying on the Glidepath. Larger aircraft operators should make every attempt to fly on the glidepath, not above it, whenever possible, to minimize vortex exposure to other aircraft.
These procedures establish a dependable baseline from which pilots of in-trail, lighter aircraft may reasonably expect to make effective flightpath adjustments to avoid serious wake vortex turbulence. At airports without GS indication, pilots should use a “300 ft to 1 mile” glidepath.
EXAMPLE: Fly 3,000 feet at 10 miles from touchdown, 1,500 feet at 5 miles, 1,200 feet at 4 miles, and so on, to touchdown.
e. Techniques for Lighter Aircraft. Pilots operating lighter aircraft behind aircraft producing strong wake vortices should consider the following techniques to assist in avoiding wake turbulence and should be aware of the wind direction and speed along the final approach path:
(1) If the pilot of the smaller following aircraft has visual contact with the preceding, larger aircraft and also with the runway, the pilot may further adjust the flightpath to avoid possible wake vortex turbulence by:
(a) Flying slightly above the glidepath and maintain that glidepath to a touchdown point beyond the touchdown point of the larger preceding aircraft.
(b) Establishing a line of sight to a touchdown point that is above and beyond the larger preceding aircraft.
(c) When possible, noting the touchdown point of the larger preceding aircraft and adjusting your touchdown point as necessary.
EXAMPLE: A puff of smoke may appear at the touchdown point of the lead aircraft; adjust your touchdown point to approximately 500 feet beyond. Be
Par 11 Page 16 aware that some Large, Heavy, or Super aircraft may require a longer touchdown point to ensure adequate clearance over the landing threshold.
(d) Landing beyond the point of landing of the preceding larger aircraft.
(2) During visual approaches, pilots may ask ATC for updates on separation and groundspeed with respect to larger preceding aircraft, especially when there is any question of safe separation from a wake turbulence perspective, and to enable the pilot to adjust the flightpath.
12. AIRCRAFT WEIGHT CLASSES. ATC uses the following aircraft weight classes for the purposes of wake turbulence separation minima:
a. Heavy. Aircraft capable of takeoff weights of 300,000 pounds or greater, whether or not they are operating at this weight during a particular phase of flight.
NOTE: A new class, the Super, above the Heavy class, has been approved on an interim basis for aircraft such as the Airbus A380 and Antonov AN225.
b. Large. Aircraft of more than 41,000 pounds maximum certificated takeoff weight up to, but not including, 300,000 pounds.
NOTE: The Boeing B757 is classified as a Large, but special wake turbulence separation criteria apply.
c. Small. Aircraft of 41,000 pounds or less maximum certificated takeoff weight.
TABLE 1. FAA WAKE SEPARATION STANDARDS (AT THE THRESHOLD) Leader/Follower Super Heavy B757 Large Small Super MRS 6 7 7 8 Heavy MRS 4 5 5 6 B757 MRS 4 4 4 5 Large MRS MRS MRS MRS 4 Small MRS MRS MRS MRS MRS NOTE: MRS: Minimum Radar Separation.
13. ADDITIONAL PILOT CONSIDERATIONS. Serious wake vortex encounters during terminal operations are rare. Pilots should be alert for possible wake vortex encounters in the following four situations.
a. Vortex Encounters.
(1) After initially descending, vortices can rebound. 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,” where the downwind vortex may rebound but with an enhanced decay rate (see Figure 7). Also, ambient thermal lifting and orographic effects (rising terrain or tree lines) can cause a vortex flow field to rise.
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(2) In certain atmospheric conditions, primarily in en route operations, vortices from Heavy and especially Super aircraft can descend more than 1,000 feet. Thus, in Reduced Vertical Separation Minimum (RVSM) operations aircraft in oceanic airspace can offset from the centerline of its track for wake turbulence avoidance (refer to the current edition of AC 91-85, Authorization of Aircraft and Operators for Flight in Reduced Vertical Separation Minimum Airspace).
(3) When crossing behind a lead aircraft, try to cross above its flightpath or, terrain permitting, at least 1,000 feet below.
(4) When a lead aircraft climbs or descends through your projected flight track, vertical separation is no longer in place and a vortex encounter is possible. Similarly, use caution when climbing or descending behind other aircraft.
b. Pilot Awareness. Pilots should be alert at all times for possible wake vortex encounters, particularly during takeoff, approach and landing operations. The pilot has the ultimate responsibility for the safe operation of the aircraft. Although ATC provides appropriate wake turbulence separation to IFR aircraft, all pilots should be aware of wake behavior and avoidance techniques and should follow the guidance and good operating procedures contained in this AC, the Aeronautical Information Manual (AIM), and applicable aircraft operations manuals.
14. WINGLETS. Winglets have been developed as a means to reduce the induced drag of a wing, making it more efficient during cruise. There is a common misperception that winglets are a means to decrease the wake vortex hazard. Studies conducted during approach and landing show no discernible differences between aircraft with or without winglets.
15. NEXT GENERATION AIR TRANSPORTATION SYSTEM (NEXTGEN) WAKE TURBULENCE INITIATIVES. Based on extensive analysis of wake vortex behavior, new procedures and separation standards are being developed and implemented. Over time, it is expected that the new separation standards will be implemented National Airspace System (NAS)-wide. Eventually, wake turbulence separation may evolve into a dynamic and specific aircraft-to-aircraft relationship based on individual aircraft wake characteristics.
a. Dependent Staggered Approaches to Closely Spaced Parallel Runways (CSPR).
FAA Order JO 7110.308, 1.5-Nautical Mile Dependent Approaches to Parallel Runways Spaced Less Than 2,500 Feet Apart, enables the use of dependent 1.5-nautical mile (NM) diagonal separation between two aircraft on CSPRs during instrument approaches with large and small aircraft as leaders in the pairing sequence. More information on these procedures is in Appendix 1, FAA Order JO 7110.308, 1.5 NM Dependent Approaches to Parallel Runways Spaced Less Than 2,500 Feet Apart.
b. Wake Turbulence Recategorization. The Wake Recategorization Program replaces the traditional maximum-certificated-takeoff-weight-based separation standard with a separation matrix based on wake vortex physics and aircraft dynamics parameters, namely wingspan, maximum takeoff weight (MTOW), final approach speed, and roll moment capability. More information on the program is in Appendix 2, FAA N JO 7110.608, Guidance for the
Par 15 Page 18 Implementation of Wake Turbulence Recategorization Separation Standards at Memphis International Airport.
c. Wake Turbulence Mitigation for Departure (WTMD). WTMD is the first automation-driven wake separation change that enables dynamic separation for departures on parallel runways separated by less than 2,500 feet based on meteorology, namely the crosswind.
More information on these procedures is in Appendix 3, FAA Order JO 7110.316, Wake Turbulence Mitigation for Departures (WTMD).
NOTE: In the near term, approval to use these new procedures will be on a runway and airport basis. Other NextGen wake turbulence initiatives are expected in the future.
ORIGINAL SIGNED by
/s/ John Barbagallo Acting Director, Flight Standards Service
Appendix 1 APPENDIX 1. FAA ORDER JO 7110.308, 1.5 NM DEPENDENT APPROACHES TO PARALLEL RUNWAYS SPACED LESS THAN 2,500 FEET APART Historically, the Federal Aviation Administration (FAA) has limited the use of parallel dependent instrument landing systems (ILS) approaches to runways with centerlines 2,500 feet or farther apart. The FAA recently approved criteria that will allow the use of the parallel dependent instrument approaches for specific airport parallel runways with centerline spacing less than 2,500 feet based on known wake vortex behavior, landing threshold stagger, and/or differential glideslopes (GS).
Criteria for Use.
• Parallel dependent ILS approaches to runways less than 2,500 feet apart can be conducted at only airport/runway combinations listed in FAA Order JO 7110.308.
• A minimum of 1,000 feet vertical or a minimum of 3 miles radar separation between aircraft will be provided until established on the localizer and cleared for the approach.
• The lead aircraft of the dependent separation pair is a Small or Large aircraft and must be assigned the lower approach based on glidepath angle or threshold location and must be established on the localizer.
• Any aircraft type may participate as the trailing aircraft in the dependent pair.
• The trailing aircraft of the dependent separation pair must be assigned the higher approach and must be established on the localizer.
• The lead and trailing aircraft will be cleared for the approach before the loss of standard separation.
• Provide a minimum of 1.5 miles radar separation diagonally with pairs of lead/trailing aircraft.
• Provide standard separation between the trailing aircraft of one pair and the leader of the next pair.
• Reduced separation is not permitted if either of the aircraft in a reduced separation pair is conducting an approach without vertical guidance.
• If the lead aircraft executes a missed approach and is larger than the trailing aircraft in the pair, the trailing aircraft will be instructed to execute a missed approach.
Definitions. For the purpose of this appendix, the following definitions are provided.
a. Lead Aircraft. The lead aircraft in the pair of reduced separation aircraft, authorized by Order JO 7110.308. The lead aircraft is restricted to be a Small or Large aircraft weight type.
b. Lead Approach. The approach assigned to the lead aircraft in a reduced separation pair.
For each Closely Spaced Parallel Runways (CSPR) pair identified in appendix A of Order JO 7110.308, the lead approach is listed first and is typically the lower approach.
c. Higher Approach. The higher approach is the approach to the runway with the staggered landing threshold or higher glidepath angle.
d. Lower Approach. The lower approach is the approach to the runway with the nonstaggered (near) landing threshold or the lower glidepath angle.
Appendix 1
e. Trailing Aircraft. The trailing aircraft in the pair of reduced separation aircraft, authorized by this order, and is not restricted by weight class.
Trailing Approach. The approach assigned to the trailing aircraft in a reduced separation pair is typically the higher approach.
FIGURE 1-1. 1.5 NM DEPENDENT APPROACHES TO PARALLEL RUNWAYS SPACED LESS THAN 2,500 FEET APART and is Assigned to Higher Approach Trailing Aircraft is Any Weight Class Aircraft 2 = Any < 2500 ft 1.5 NM Aircraft 3 = Aircraft 1 = 3 Small or Large Small or Large ...
Standard Separation Lead Aircraft is Either a Small or Large and is Assigned to Lower Approach Page 2
Appendix 2 APPENDIX 2. FAA N JO 7110.608, GUIDANCE FOR THE IMPLEMENTATION OF
WAKE TURBULENCE RECATEGORIZATION SEPARATION STANDARDS AT
MEMPHIS INTERNATIONAL AIRPORT The Federal Aviation Administration (FAA) recently approved a recategorization (RECAT) of wake turbulence separation minima from the current standard to a new standard (RECAT Phase I). This approval was based on years of joint research and development by the FAA, Eurocontrol, scientific experts in wake, and experts in safety and risk analysis. Categories are now based on weight, certificated approach speeds, and wing characteristics, along with special consideration given to aircraft with limited ability to counteract adverse rolls. RECAT places aircraft into six (6) categories (labeled A-F) for both departure and arrival separation.
Through a detailed system safety analysis, the six categories prove to be as safe, or safer, than today’s total separation standards while providing the opportunity for increased efficiency for National Airspace System (NAS) operations. As RECAT is implemented at selected airports in the NAS, pilots may see changes (both reductions or increases) in the required and applied wake turbulence separation distances for some aircraft, while most will not notice any changes at all.
Table 2-2 details the RECAT wake separation standards.
NOTE: RECAT is in effect at Memphis International Airport (MEM) and Louisville International-Standiford Field (SDF), with plans to expand to other airports in the future.
AIRCRAFT WAKE CATEGORIES. For the purposes of Wake Turbulence Separation Minima, aircraft are categorized as Category A through Category F. Each aircraft is assigned a category based on wingspan, approach speed and maximum takeoff weight (MTOW). Table 2-1 provides examples of some of the aircraft within the Categories:
a. Category A. Aircraft capable of MTOW of 300,000 pounds or more and a wingspan greater than 245 feet.
b. Category B. Aircraft capable of MTOW of 300,000 pounds or more and a wingspan greater than 175 feet and less than or equal to 245 feet.
c. Category C. Aircraft capable of a MTOW of 300,000 pounds or more and a wingspan greater than 125 feet and less than or equal to 175 feet.
d. Category D. Aircraft capable of a MTOW of less than 300,000 pounds and a wingspan greater than 125 feet and less than or equal to 175 feet; or aircraft with a wingspan greater than 90 feet and less than or equal to 125 feet.
e. Category E. Aircraft capable of a MTOW greater than 41,000 pounds with a wingspan greater than 65 feet and less than or equal to 90 feet.
f. Category F. Aircraft capable of a MTOW of less than 41,000 pounds and a wingspan less than or equal to 125 feet, or aircraft capable of a MTOW less than 15,500 pounds regardless of wingspan, or a powered sailplane.
Appendix 2 TABLE 2-1. EXAMPLE AIRCRAFT ASSIGNMENT TO PROPOSED SIX CATEGORY SYSTEM NOTE: List is not all-inclusive. A complete list can be found at:
http://www.faa.gov/air_traffic/publications/media/aircraft_characteristics.pdf.
Category A Category B Category C Category D Category E Category F A380 B747 series MD11 B757 series AT72 E120 AN-225 A340 series B767 B737 series RJ100 B190 End of list B777 series A306 A320 series RJ85 C650 A330 series A310 B727 series B463 H25B B787 series DC8 MD80 series B462 C525 C-5 DC10 F50 E170 GA multiengine aircraft B-52 C-17 E190 CRJ1/2 GA single engine aircraft IL-96 C-135 B717 CRJ7/9 B-1 GLF5 AT45 B-2 DC95 AT43 DC93 GLF4 DH8D SF34 F100 DH8A/B/C F70 E135/145 TABLE 2-2. RECAT WAKE SEPARATION STANDARDS Leader Follower (Nautical Mile)
A B C D E F A MRS 5 6 7 7 8 B MRS 3 4 5 5 7 C MRS MRS MRS 3.5 3.5 6 D MRS MRS MRS MRS MRS 5 E MRS MRS MRS MRS MRS 4
F MRS MRS MRS MRS MRS MRS NOTE: MRS: Minimum Radar Separation.
Appendix 3 APPENDIX 3. FAA ORDER JO 7110.316, WAKE TURBULENCE MITIGATION FOR
DEPARTURES (WTMD) WTMD allows a reduction in required wake turbulence separation for aircraft departing on specifically authorized parallel runways separated by less than 2,500 feet based on prevailing and predicted wind and weather conditions. Current wake separation standards require that a 2-minute delay or up to 5 miles radar separation be applied to a subsequent departure following a Heavy/B757 aircraft departing from an adjacent Closely Spaced Parallel Runway (CSPR) (parallel runways separated by less than 2,500 feet with the threshold offset by less than 500 feet). A safety analysis has shown these wake separation standards can be eliminated if the required conditions for use of WTMD are in place. See Figure 3-1, Wake Movement with Crosswind Component.
Under these conditions, the wake created by the departing Heavy/B757 aircraft (excluding Super aircraft) does not affect subsequent departures on the CSPR upwind runway. The upwind runway can be considered wake free– that is, unaffected by the wake of the departing Heavy/B757 aircraft.
FIGURE 3-1. WAKE MOVEMENT WITH CROSSWIND COMPONENT
Appendix 3 The Federal Aviation Administration (FAA) recently approved the WTMD procedure. The system uses wind information at the surface and incrementally up to about 1200 feet above ground level (AGL) to ensure actual crosswinds and a conservative forecast of future crosswinds are sufficiently strong to allow the reduced separation operations. The WTMD system has been validated through a comprehensive collection and analysis of departure wake turbulence data.
When the air traffic controller enables WTMD, a display informs the local controller which runway has been identified as wake independent from Heavy/B757 aircraft departure operations from the other parallel runway. The system also has an automatic alert to cease WTMD operations when monitored winds or forecasted winds are falling out of the conservative crosswind criteria required for reduced separation operations. WTMD operations will be included in the automated terminal information service (ATIS) message and communicated to the pilots via pilot/controller radiotelephony during transition to WTMD operations. The pilot will continue to have the option to request 2 minutes separation (or 3 minutes separation, if applicable), instead of controller applied reduced distance separation when WTMD is enabled.
Figure 3-2 presents a graphic of reduced separation operations when WTMD is enabled.