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Wake Turbulence Hazard - A Pilot Check List
From SKYbrary Wiki
| Article Information | ||
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| Category: | Wake Vortex Turbulence | 
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| Content source: | SKYbrary | 
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| Content control: | EUROCONTROL | 
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Contents |
Basic Principle
The vortices generated at the wing tips of an airborne fixed wing aircraft or from the rotors of a helicopter in forward flight create transient rotational turbulence which trails behind the aircraft and may cause sudden un-commanded roll to affect a following aircraft, perhaps at a sufficient rate of roll to disconnect the autopilot if engaged.
Opposing the induced roll moment using normal roll control (aileron and roll spoiler) is usually effective except when the wingspan and ailerons of the affected aircraft do not extend beyond the rotational flow of the two vortices, which can occur when the following aircraft is much smaller than the leading aircraft.
The minimum traffic separation distances for aircraft under ATC Control have consistently been shown to be sufficient to ensure that any loss of control caused by an encounter with wake turbulence will always be transient and easily recoverable except for some cases of spacing on approach to land or on initial climb following take off. To cover these circumstances, and various more complex permutations of runway use, minimum separation distances and times have been promulgated by ICAO.
Risk Control
- Know the full specification of the Wake Turbulence Separation Minima and any national variations which you are liable to encounter (check the State AIP/AICs)
- When under ATC control on approach, use the TCAS Display to provide an approximate check on spacing behind any leading aircraft and be sure you have established the aircraft type ahead so as to know what minimum distance behind is necessary.
- If the Autopilot is engaged for an approach at or near to minimum recommended spacing from an aircraft ahead, ensure PF is prepared for manual recovery from any sudden roll which is at a high enough rate to cause simultaneous un-commanded autopilot disconnection.
- Ensure that all cabin crew are secured in their seats before final approach commences.
- When in sequence behind a larger category aircraft for departure, be careful to time any required separation from the point at which vortices begin (Vr) rather than the start of roll. Note that the take off roll will be less distance and take less time for a small aircraft than a larger one.
- Where considered necessary be prepared to remind departure ATC of the minimum time you require behind a preceding heavier aircraft and do not accept instructions to begin your take off roll before the prescribed time separation is achievable at the anticipated point of rotation.
- The practice of some aircraft operators of including in the pre-flight advice to passengers an invitation to keep their seat belts done up even when the seat belt sign is off unless moving around the cabin will minimize the risk of passenger injury if there is an unexpected encounter with turbulence
- En route, and especially when level at cruise altitude, use the TCAS Traffic Display to maintain situational awareness of other aircraft in the vicinity which appear to be on similar tracks ahead and at or above your own level. Be prepared to query aircraft type with ATC if you have reason to suspect that it may be of a much higher weight than your own aircraft. Noting that wake vortex decay has been shown to be much slower in less dense and more stable air at high altitude than it is near the ground, and that significant encounters with wake turbulence from larger aircraft at more than 1000 ft vertical or 5nm horizontal separation do occur, be prepared to select seat belt signs to ‘on’ and instruct working cabin crew to secure themselves for a precautionary interval.
- Note the revisions to approach and departure minima issued for the Airbus A380-800 see Airbus A380 Wake Vortex Guidance and remember that any en route encounters may invite a greater degree of caution than would otherwise be appropriate.
- If flying an approach in a small aircraft, and an encounter with wake vortex turbulence is considered a risk, ensure that the vertical profile flown is steeper than that being flown by preceeding aircraft on the same approach or by any aircraft on a parallel or crossing approach
Related Articles
Further Reading
- Good Aviation Practice - Wake Turbulence by Civil Aviation Authority of New Zealand