Letter of the Week: Airbuses Fly Like a Video Game
AVmail: June 6, 2011
I would like to offer my comments and perspective with regard to the Air France Flight 447 accident:
I have been a A-330 captain since 2003 and have over 4500 hours in the aircraft. While many A-320 pilots undoubtedly have more series time, I believe this probably makes me one of the most experienced A330 pilots in the world.
When asked how I like the aircraft, I tell people that there is likely no easier airplane to take over an ocean, and that the systems design and presentation is superb.
That said, the automation is more complex and less intuitive than necessary, and the pilot-aircraft interface is unlike that of a conventional aircraft. Most important with regard to this accident is the fly-by-wire sidestick control.
The sidestick itself has a very limited range of motion, making inadvertent over-control very easy. Of even greater significance, the stick itself provides no “feel” feedback to the pilot. That is, unlike a conventional aircraft, the pilot does not get a sense through pressure of how much input is being sent to the control surfaces.
The most important advice I give to pilots new to the Airbus is to treat the aircraft not as an airplane, but as a video game. If you wait for the sidestick to tell you what you are doing, you will never get an answer.
Taking into consideration that Air France 447 was at FL 350 (where the safe speed envelope is relatively narrow), that they were in the weather at night with no visible horizon, and that they were likely experiencing at least moderate turbulence, it does not surprise me in the least that the pilots lost control of the aircraft shortly after the autopilot and autothrust disconnected.
Let’s keep in mind that these are not ideal conditions for maintaining controlled flight manually, especially when faced with a sudden onslaught of warning messages, loss of autofllght, confusing airspeed indications, and reversion to “alternate law” flight control, in which certain flight envelope protections are lost.
A very bad Airbus design feature is thrust levers that do not move while in autothrust. They are instead set in a detent which would equal climb trust in manual mode. If the pilots did not reset the thrust levers to equal the last cruise power setting, they likely eventually ended up in climb power, making it difficult to reset the proper cruise power setting and adding to what was likely already a great deal of confusion.
But the real problem probably occurred immediately after the pilot flying grabbed the sidestick and took over manually. Unfortunately, airline pilots rarely practice hand-flying at high altitude, and almost never do so without autothrust engaged. As a result, we forget that the aircraft is very sensitive to control inputs at high altitude, and overcontrol is the usual result. Because the Airbus sidestick provides no feedback “feel” to the pilot, this problem is dramatically compounded in this aircraft.
I believe the Air France pilot grabbed the sidestick, made an immediate input (because as pilots, that’s what we tend to do), and quickly became quite confused as to what the aircraft was truly doing. This confusion likely was exacerbated by fixating on airspeed indications that made no sense while trying to find a power setting with no airspeed guidance.
When transitioning from autopilot to manual control at altitude in the Airbus, the most important thing to do at first is nothing. Don’t move a thing, and then when you do, gently take hold of the sidestick and make very small inputs, concentrating on the flight director (which, in altitude hold, should still have been providing good guidance).
Of course, this is much easier said than done with bells and whistles going off all over the place, moderate turbulence and a bunch of thunderstorms in the area. As I said before, treat it like a video game.
So why did the Air France pilot find himself at the limits of sidestick travel, and then just stay there, maintaining a control input that simply could not logically be correct? When things go really bad and we are under intense pressure, it is human nature to revert to what we know from previous experience. Remember, the Airbus flies like no other aircraft in that the sidestick provides no feedback to the pilot. It is a video game, not an airplane.
I believe the Air France pilot unintentionally fell back on all of his previous flying experience, in which aircraft controls “talked” to him when he moved them. Distracted by many confusing inputs, he instinctively expected to be able to control the aircraft by “feel” while dividing his attention to address other matters.
I’ve seen it happen in the simulator, and in an Airbus this is a sure way to lose control of the aircraft and is possibly the most dangerous aspect of Airbus design philosophy.
One last note: Airbus pilots often claim that the aircraft “can not be stalled.” When the flight controls are in “normal law” this is a reasonably true statement. However, in “alternate law,” as was the case here, stall protection can be lost. If we ever practiced this in the simulator, I don’t remember it.
Lest anyone think I am blaming the Air France pilots for this accident, let me be clear. Despite all of my experience in the aircraft, I am not the least bit certain that I would have been able to maintain control under the same circumstances.
I do feel certain that were you to spring this scenario on pilots in a simulator without warning less than half of them would have a successful outcome.
Safely flying the 320, 330 and 340-series Airbus requires something of a non-pilot mindset.
We have spoken with the writer of this letter to confirm his identity and honored his request for anonymity.
For another analysis of the trials and challenges of flying an A330, be sure to listen to _Friday’s podcast with airline pilot Jason Goldberg: