Okay, first the disclaimers; not pilot – engineer. Not aeroplane engineer – CT/MRI Scanner engineer/SLF so, comparable technology. Yes, I have read most of the threads devoted to AF447, but they keep overtaking me. Although fascinating, I have to say it’s a damned laborious business for an outsider, because of the inevitable TLAs (three letter acronymns).
My sources are almost exclusively what I have read on here and only from those whose posts appear the most authoritative. No newspaper or media reports were used in the making of this post, which, is in the form of either unresolved thoughts or questions arising from information read here. I suppose I’m really just trying to summarise what I have understood from this mass of data and in the hope that it will help others.
I was looking back at a draft I wrote to contribute to the first AF447 thread (but never did) when weather, the avoidance of it and the location of the wreck were the main topics, as so few facts were then known. And, my goodness, how this and other threads have moved on? Now, a remarkable three years later, the Flight Data Recorder and the Cockpit Voice Recorder have been found, against all expectation, and analysed to reveal what appears, to this Engineer SLF, a frankly terrifying set of circumstances.
Through choice or lack of planning, AF447 flew – at 35,000ft – near to a large, complex storm cell that other aircraft had avoided. This, directly, lead to icing of the pitots and temporary loss of ‘Air Data’ – information from the air outside – which meant loss of accurate air speed indication.
This condition lead inevitably and almost immediately to the autopilot and autothrottle releasing the aeroplane into the hands of the two F/Os remaining in the cockpit after the Captain went off for his legal, though given the circumstances of weather, ill advised, rest break. Nevertheless, an ‘Unreliable Air Speed’ condition was never formally declared in the cockpit and no ‘procedure’ instigated.
Although the aeroplane had been straight, level and surprisingly stable – given the proximity of the storm – concern about overspeed was immediate and the PF (the least experienced F/O) throttled back and pulled back on the side stick. This instigated an almost 2000ft/min climb which continued – with the speed dropping all the time – to circa 38,000ft.
The PNF (the most experienced F/O) meantime was trying to make sense of what was happening as air data intermittently became ‘valid’ then ‘invalid’ again. All this time PF was pulling back on the sidestick almost, but not quite continuously. At or near the top of the climb, with speed bleeding away quite dangerously, PF hit TOGA – basically firewalling the throttles to a pre-set power output – which always pitches the aeroplane nose up unless counteracted, adding to the already dangerous Angle of Attack. The speed thus reduced still further and, with the stick still pulled back, the wings stalled and the aeroplane began to descend, very nose up.
PNF became very concerned, but equally confused as to what was happening, even though the altitude and vertical speed indications were working on his side, although ASI was not always valid. The stall warning operated, but neither pilot acknowledged it and no obvious action was taken immediately. As the speed dropped still further – below 60kts? – the stall warning stopped because it had fallen below its ‘authority band’. When PF several times released the sidestick, the aeroplane tried to level out and the speed temporarily rose, causing the stall warning to again sound as it re-entered its authority. This warning again drove PF to pull back on the sidestick, confusing PNF still further, if possible.
When the Captain returned from wherever in the aeroplane he had been, he elected to take the centre seat, not the LHS controls. He asked a number of questions, the answers to which served only to confuse any readings he might have taken from the instruments. During this time, PF was still pulling back on the sidestick and it was pretty much in this state that the aeroplane hit the sea at between 7000 and 10,000ft/min.
Apart from the initial blocked pitot/ Air Data failure – a condition experienced by 36 other aircraft of the same type – there was no other failure of an aircraft system.
I am no pilot, although I have flown light aircraft and have had a deep interest in aeroplanes and flying since I was eight, but even I know that pulling back continuously on the elevator control will, eventually kill you. I remember being deeply impressed by the low speed pass into steep, turning climbout of an early FBW Airbus at Farnborough, because I knew then, that to do what that pilot had just done in almost any other aeroplane, would certainly kill him. But I also know doing that at low altitude is quite a different thing from doing it at almost the maximum height for the weight.
In my really quite humble opinion, the Captain did not assert enough clear thinking authority and was quite ill advised to leave the cockpit when he did, but did not cause the accident. PNF had probably figured out what was happening, but could not square the symptoms with what he thought PF was doing. He assumed - and more or less had to assume – that PF was doing all the right things to control the aeroplane and when he did take control, a quirk of the stall warning system prompted PF to effectively snatch back control and keep pulling back. When the Captain returned, he too couldn’t even begin to understand what PF had been, and still was, doing.
The software protocols of the Airbus – an otherwise beautiful machine – have again been called into question and I don’t suppose for a moment the boys and girls in Boeing’s design/ build teams are going to say; “Tell you what, how ‘bout a sidestick upgrade for the 773, the 748 and the 787?” any time soon. For interested SLF, this accident is a very, very worrying revelation.