AF447 final crew conversation - Thread No. 1
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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.
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.
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@ Conf iture:
Quote:
Originally Posted by A33Zab
The yellow AOA indicator line [Current AOA] would have been at the bottom of the SLOW side of the scale
I was looking at the FCOM and things are described a bit differently :
Quote:
Actual Speed Reference Line (Yellow) :
This fixed reference line next to a yellow triangle, indicates the aircraft’s current speed.
Originally Posted by A33Zab
The yellow AOA indicator line [Current AOA] would have been at the bottom of the SLOW side of the scale
I was looking at the FCOM and things are described a bit differently :
Quote:
Actual Speed Reference Line (Yellow) :
This fixed reference line next to a yellow triangle, indicates the aircraft’s current speed.
.....but you are absolutely right the Yellow line is fixed - like the normal speed reference - and the background is moving.However the function remains the same......CAS vs AOA.
So that yellow line stays in the middle and probably and hopefully the GREEN area with the target speed (GREEN triangle) remains visible at the top of the scale whatever the current stall speed/AoA is.
For the Red SLOW area :
Quote:
This red area indicates the speeds that are lower than the stall speed.
For the Red SLOW area :
Quote:
This red area indicates the speeds that are lower than the stall speed.
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For now, an image from A380 AMM but too fast for AOA....
For too slow, you would be in the bottom red sector.
The arrow shapes seem a bit counter intuitive since they bear opposite relationship to the direction you might want to move the nose to recover.
Glad they didn't put that in my flying machine for landing aboard ship.
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MB, me too. Too much info to sort out when you are FUBARed. Keep it simple. Needle, ball and airspeed always worked in the past, now it is much more complex with computers flying most airplanes, especially the Airbus with pilots monitoring. Flying the 757 out of San Jose, Costa Rica one day with a check airman as my right seater on my initial captain check out our clearance got changed to an unlimited climb short cutting the level off and transition. He had the FMC so screwed up as I was making a right climbing turn and the FD was showing a left diving turn so ignored it until he caught up. Automation is fine if it is your helper, not your God. AF447 would not have happened with real aviators flying in my opinion.
Full back stick for over 3 minutes in a stall isn't what we are taught because it always kills you, guaranteed.
Full back stick for over 3 minutes in a stall isn't what we are taught because it always kills you, guaranteed.
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Me too. It was fun when we were flying. Now it looks like just a job with everything being monitored to verify you were stabilized below 1,000 etc. I liked it when you could do a roll over Mt Whitney inverted descending into Bishop in a charter jet. Guess the FAA can't violate me for something I did 35 years ago. It had no purpose, it was just fun.
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A33Zab,
Thanks for the illustration, it does clarify things on the BUSS.
As Machinbird I have to say I find this indication for an extreme case somehow counter intuitive ... Would be curious to experiment it in a simulator.
Thanks for the illustration, it does clarify things on the BUSS.
As Machinbird I have to say I find this indication for an extreme case somehow counter intuitive ... Would be curious to experiment it in a simulator.
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Yes, I would gladly do the Mt Whitney maneuver again but am retired and do boats in the Keys now. I will always remember the event but it wasn't that big a deal. It sure was fun though. It is hard to screw up when once you clear the peak at 500 ft you have almost 10,000 ft below you in the valley.
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With respect but the BUSS is not intended for Nimitzclass landings nor for inverted maneuvres......
Its only goal is to supply a speed vs AOA indication in - remote situations - when normal speed indications are not available.
IMO - Fly The Green - seems not be too difficult unless your colorblind and don't understand the meaning of FAST and SLOW.......
'Stalled' indication (some copy paste work)
Its only goal is to supply a speed vs AOA indication in - remote situations - when normal speed indications are not available.
IMO - Fly The Green - seems not be too difficult unless your colorblind and don't understand the meaning of FAST and SLOW.......
'Stalled' indication (some copy paste work)
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A33Zab;
Thanks for the information on the BUSS.
Some time ago a post claimed that it displays AoA and nothing else. Would it be possible to retrieve information on how it works internally, i.e. what input data it uses and how these data are combined/processed to drive the display?
P.S.
See for example AF447 UAS by Joelle Barthe
Thanks for the information on the BUSS.
Some time ago a post claimed that it displays AoA and nothing else. Would it be possible to retrieve information on how it works internally, i.e. what input data it uses and how these data are combined/processed to drive the display?
P.S.
See for example AF447 UAS by Joelle Barthe
The BUSS is optional on A320/A330/A340. It is basic on A380, being part of the ADR Monitoring functions.
This indication is based on angle of atack (AOA) sensor information, and is therefore not affected by erroneous pressure measumements.
The BUSS comes with a new ADIUR standar (among other new system standards), where the AOA information is provided through the IRs and nor through the ADRs. This enables selecting all ADRs off without loosing the STALL WARNING PROTECTION.
The AOA information provides a guidance area in place of the speed scale. When the crew selects all ADRs OFF, then:
- The Back-Up Speed Scale replaces the PFD speed scale on both PFDs,
- GPS Altitude replaces the Altitude Scale on both PFDs.
The Back-Up Speed Scale then enables to fly at a safe speed, i. e. above stall speeds, by adjusting thrust and pitch.
This indication is based on angle of atack (AOA) sensor information, and is therefore not affected by erroneous pressure measumements.
The BUSS comes with a new ADIUR standar (among other new system standards), where the AOA information is provided through the IRs and nor through the ADRs. This enables selecting all ADRs off without loosing the STALL WARNING PROTECTION.
The AOA information provides a guidance area in place of the speed scale. When the crew selects all ADRs OFF, then:
- The Back-Up Speed Scale replaces the PFD speed scale on both PFDs,
- GPS Altitude replaces the Altitude Scale on both PFDs.
The Back-Up Speed Scale then enables to fly at a safe speed, i. e. above stall speeds, by adjusting thrust and pitch.
Last edited by HazelNuts39; 24th Jan 2012 at 09:06. Reason: P.S.
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I quite agree, Mac - placing that in front of our 447 crew would, I think, have merely hastened their demise (if that was possible)
HN39 - if I read you correctly there, the BUSS is 'deducing' AoA from inertial GS/FPA and attitude?
HN39 - if I read you correctly there, the BUSS is 'deducing' AoA from inertial GS/FPA and attitude?
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I have to admit, I didn't find the 'slow/fast' message one that leapt out and told me what to do without my first having to think about it - and when a pilot finds him/herself at 101% overload - (as virtually all of us would be in a situation like the one the AF FOs found themselves) - having to think about what the display is telling you is the very last thing you need.
I'll accept that the potential confusion might (should?) have been covered during conversion.
I'll accept that the potential confusion might (should?) have been covered during conversion.
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As the name says it is a back-up speed scale replacing the standard speed tape. The red-yellow-green tape moves in the same sense as the standard speed tape. There is a target speed indicated by a green area and triangle.
Numbers have simply been replaced by colors. How is that confusing or counterintuitive?
Numbers have simply been replaced by colors. How is that confusing or counterintuitive?
Plastic PPRuNer
"Numbers have simply been replaced by colors. How is that confusing or counterintuitive"
Something like
GPS Speed 60kts
would be fairly attention getting....
Something like
GPS Speed 60kts
would be fairly attention getting....
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Originally Posted by BOAC
HN39 - if I read you correctly there, the BUSS is 'deducing' AoA from inertial GS/FPA and attitude?
Originally Posted by Mac the Knife
Something like "GPS Speed 60kts" would be fairly attention getting....
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However, by side-effect, BUSS might have saved them - if you believe off/on SW killed them, read on...
HN39 - if I read you correctly there, the BUSS is 'deducing' AoA from inertial GS/FPA and attitude?
Now, the interesting thing is the stall warning comment - which says to me that as well as feeding the BUSS, the re-routed AoA signal from the new ADIRU also feeds the SW logic. Which, I think, means that SW would be continuous even if airdata calculations invalidate AoA data on that side of the ADIRU, and that would apply whether the BUSS is engaged (ADRs off) or not.
Not saying BUSS would have helped, but if anyone's thinking that BUSS wouldn't have helped because it's useless above FL26 etc. and that the on/off SW was the killer... then they might want to reconsider.
