Par 9 Page 13 FIGURE 16. CRITICAL TAKEOFF SITUATION AND CROSSING DEPARTURE COURSES
g. Intersection takeoffs - same runway - be alert to adjacent large aircraft operations, particularly upwind of your runway. If intersection takeoff clearance is received, avoid subsequent heading which will cross below a larger aircraft’s path.
h. Departing or landing after a larger aircraft executing a low 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 missed approach or a touch-and-go landing, particularly in light quartering wind conditions. You should ensure that an interval of at least 2 minutes has elapsed before your takeoff or landing.
i. En route VFR (1,000-foot altitude plus 500 feet). Avoid flight below and behind a larger aircraft’s path. If a larger aircraft is observed above on the same track (meeting or overtaking), adjust your position laterally, preferably upwind.
10. HELICOPTERS. A hovering helicopter generates a downwash from its main rotor(s) similar to the “prop wash” of a conventional aircraft. 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 exceptionally strong wake turbulence (see figure 17).
Page 14 Par 10 FIGURE 17. HELICOPTER VORTICES
11. JET ENGINE EXHAUST.
a. During ground operations, 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 during ground operations.
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b. Engine exhaust velocities, generated by larger jet aircraft during ground operations and initial takeoff roll, dictate the desirability of lighter aircraft awaiting takeoff to hold well back of the runway edge at the taxiway hold line. Also, it is desirable to align the aircraft to face any possible jet engine blast effects. Additionally, in the course of running up engines and taxiing on the ground, pilots of larger aircraft should consider the effects of their jet blasts on other aircraft, vehicles, and maintenance and servicing equipment.
12. PILOT RESPONSIBILITY.
a. Government and industry groups are making concerted efforts to minimize or eliminate the hazards of trailing vortices. However, the flight disciplines necessary to ensure vortex avoidance during VFR operations must be exercised by the pilot. Vortex visualization and avoidance procedures should be exercised by the pilot using the same degree of concern as in collision avoidance.
b. Pilots are reminded that in operations conducted behind all aircraft, acceptance of instructions from air traffic control (ATC) in the following situations is an acknowledgment that the pilot will ensure safe takeoff and landing intervals, and accepts the responsibility for providing wake turbulence separation.
(1) Traffic information,
(2) Instructions to follow an aircraft, and
(3) The acceptance of a visual approach clearance.
c. For operations conducted behind heavy aircraft, ATC will specify the word “heavy” when this information is known. Pilots of heavy aircraft should always use the word “heavy” in radio communications.
d. Heavy and large jet aircraft operators should use the following procedures during an approach to landing. These procedures establish a dependable baseline from which pilots of in-trail, lighter aircraft may reasonably expect to make effective flight path adjustments to avoid serious wake vortex turbulence.
(1) Pilots of aircraft that produce strong wake vortices should make every attempt to fly on the established glidepath, not above it; or, if glidepath guidance is not available, to fly as closely as possible to a “3 to 1” glidepath, not above it.
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.
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(2) Pilots of aircraft that produce strong wake vortices should fly as closely as possible to approach course centerline or to the extended centerline of the runway of intended landing as appropriate to conditions.
e. Pilots operating lighter aircraft on visual approaches in-trail to aircraft producing strong wake vortices should use the following procedures to assist in avoiding wake turbulence. These procedures apply only to those aircraft that are on visual approaches.
(1) Pilots of lighter aircraft should fly on or above the glidepath. Glidepath reference may be furnished by an ILS, by a visual approach slope system, by other ground-based approach slope guidance systems, or by other means. In the absence of visible glidepath guidance, pilots may very nearly duplicate a 3-degree glideslope by adhering to the “3 to 1” glidepath principles.
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.
(2) If the pilot of the lighter following aircraft has visual contact with the preceding heavier aircraft and also with the runway, the pilot may further adjust for possible wake vortex turbulence by the following practices:
(a) Pick a point of landing no less than 1,000 feet from the arrival end of the runway.
(b) Establish a line-of-sight to that landing point that is above and in front of the heavier preceding aircraft.
(c) When possible, note the point of landing of the heavier preceding aircraft and adjust point of intended landing as necessary.
EXAMPLE:
A puff of smoke may appear at the 1,000-foot markings of the runway, showing that touchdown was that point; therefore, adjust point of intended landing to the 1,500-foot markings.
(d) Maintain the line-of-sight to the point of intended landing above and ahead of the heavier preceding aircraft; maintain it to touchdown.
(e) Land beyond the point of landing of the preceding heavier aircraft.
(3) During visual approaches pilots may ask ATC for updates on separation and groundspeed with respect to heavier preceding aircraft, especially when there is any question of safe separation from wake turbulence.
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(4) Aircraft Classes. For the purposes of Wake Turbulence Separation Minima, ATC classifies aircraft as Heavy, Large, and Small as follows:
(a) Heavy-Aircraft capable of takeoff weights of more than 255,000 pounds whether or not they are operating at this weight during a particular phase of flight.
(b) Large-Aircraft of more than 41,000 pounds, maximum certificated takeoff weight, up to 255,000 pounds.
(c) Small-Aircraft of 41,000 pounds or less maximum certificated takeoff weight.
13. PILOT AWARENESS INTERVENTION. 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 above ground level (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, nor 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. In view of 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.
James J. Ballough Director, Flight Standards Service