Wake? Wait!

The standard advice to avoid a wake turbulence encounter is to wait a bit, to give some room when taking off or landing right behind a large aircraft. And that is good, practical, physics-based advice.

But what about when you hit wake turbulence and have to recover?

What’s being rediscovered is when actually encountering serious wake turbulence, the best thing to do is: Nothing. Well, not just nothing, but initially just wait. That’s right, wait. You may be rapidly going inverted but don’t do anything yet. Breathe for a second. Resist the strong urge from our primal flying nature to quickly move the controls. Immediate yanking and banking has been reinforced by decades of minimal ‘unusual attitude’ training. But but but, wait — there may be more man-made tornados coming. Only once clear, in calmer air, start the recovery control inputs.

The current Paris Air Show edition of Aviation Week has an article on this topic titled ‘Wake Worries: Industry takes a fresh look at turbulence caused by wake vortices in cruise flight’ (paywall). The starting point is the accident report of Bombardier Challenger 604 business jet having a very serious wake encounter with an Airbus A380 (excellent Av Herald report) over the Arabian Sea on 7 January 2017. While the business jet landed safely, it was a total hull loss and caused several severe injuries. The ending point is talk of an upcoming EASA safety bulletin that is expected to instruct pilots to avoid rapid-roll control reversals and to avoid large rudder deflections.

Let’s read that again — avoid rapid-roll control reversals and avoid large rudder deflections.

Photo of the interior of D-AMSC after the upset

This is opposite of the airline simulator training I’ve always had, training that quickly sets you up in an unusual attitude and says ‘Recover!’. And it’s the opposite reaction that most of us have to the plane rapidly banking one way or another. Do nothing?? But it’s not new advice. The FAA’s Advisory Circular 90-23G ‘Aircraft Wake Turbulence’ dated 2/10/14 explains that:

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.

Wait till you are out of the wake, because the spinning nature of the two vortex flow fields mean a roll to the right may be almost immediately followed by a roll to the left, and large control inputs to counter the first roll may make the second one much worse. Get into calm air before starting the recovery.

Two things to note. One, this subject is a small part of the larger field of upset recovery. I think one of the best (free, smart) places to start reading about this is the Royal Aeronautical Society Aeroplane Upset Recovery Training, History, Core Concepts & Mitigation paper online. And two, like most things, prevention is better than recovery.

I guess training organizations will start teaching this ‘old knowledge’ now spotlighted by new accidents. But the history of training for complex upset events suggests it will be a quick review, not a through aerobatic aerodynamic understanding. And if a large plane’s wake tips me over, I hope I have the mental fortitude to stay calm and wait a few seconds before yanking in some big recovery control inputs.

Wake? Wait!

 

Bonus bit for beer bets: The FAA AC notes that “studies conducted during approach and landing show no discernible [wake turbulance] differences between aircraft with or without winglets.”

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7 thoughts on “Wake? Wait!

  1. This has proven to be one of the most useful aviation blog I’ve ever subscribed to.

    Joe schena
    A320 captain

  2. Airbus Safety First #21 has an interesting article on wake turbulence with reference to Airbus FBW that is also well
    worth a read.

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