AF471 - Nov 16th 2011 - Final Report
Ut Sementem Feeceris
The NO DH was removed about three years ago - why, I have no idea.
It strikes me as particularly stupid because now at 20' or 25' right in the middle of the RADALT 50-40-30- you get a "MINIMUMS" with a requirement to confirm you can see 1 light, respond with "Continue" or "Go-around Flaps". Additionally the FLARE call comes in at 30-40 from the PNF. It's a mess.....and only in France -why?
Regarding this incident.....lack of understanding of A/c systems as root cause? If you ONLY have to push the TOGA buttons to initiate (does the AP automatically pitch to 15 degrees?) I don't really see how it could be made any simpler. Airbus - just push the levers till they won't go any further and the autos (if functioning correctly) do the rest - easy. If they're not working and you are unable to pitch to 15 manually/promptly, perhaps you should consider an alternative career. Are the TOGA buttons and A/THR disconnect buttons close together on the 777 levers?
It strikes me as particularly stupid because now at 20' or 25' right in the middle of the RADALT 50-40-30- you get a "MINIMUMS" with a requirement to confirm you can see 1 light, respond with "Continue" or "Go-around Flaps". Additionally the FLARE call comes in at 30-40 from the PNF. It's a mess.....and only in France -why?
Regarding this incident.....lack of understanding of A/c systems as root cause? If you ONLY have to push the TOGA buttons to initiate (does the AP automatically pitch to 15 degrees?) I don't really see how it could be made any simpler. Airbus - just push the levers till they won't go any further and the autos (if functioning correctly) do the rest - easy. If they're not working and you are unable to pitch to 15 manually/promptly, perhaps you should consider an alternative career. Are the TOGA buttons and A/THR disconnect buttons close together on the 777 levers?
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I was told the reason was that the French authorities wanted the pilot to make the decision and not the aircraft. Hence the DH.
They clearly wanted the crew flying the aircraft and not the aircraft flying the crew.....ironic eh.....
They clearly wanted the crew flying the aircraft and not the aircraft flying the crew.....ironic eh.....
Ut Sementem Feeceris
I'd heard that as a reason....but dismissed it as too ludicrous to be true. By introducing a decision at 25', a press of the wrong button......followed by "analysis" of the error.....doesn't exactly leave a lot of time. And, again, why is France the only Country in Europe to introduce this? They must know best - right?
I've never understood the "one light" visual requirement on a CAT IIIB with DH either. Like you say, A4, it doesn't leave a lot of time at all - and what happens if the "one light" you see (and on which you base your decision to continue) turns out to be, for example, a runway edge light, or something on the airfield periphery?
(Admittedly it's unlikely, such is the accuracy and reliability of both ground and airborne equipment these days, but then you come back to the question - why bother with the "one light" requirement at all?)
(Admittedly it's unlikely, such is the accuracy and reliability of both ground and airborne equipment these days, but then you come back to the question - why bother with the "one light" requirement at all?)
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He saw the ground at 250 ft. Having visual references and, knowing that the landing was possible, his plan of action was to land. The NOLAND3 warning, making mandatory a go-around, led to confusion and to a change in his plan of action. He thus progressively moved the throttle levers forwards.
CONTACT - CONTINUE
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I am not a B777 pilot, but I have flown Boeing a/c with Land 2 & Land 3 annuciations. Land 2 did not require a G/A it just changed the DH from Cat 3A to CAT 2 and it was still an autoland. So why the G/A? I would have expected that before executing an LVO ILS there would have been an extensive briefing of what to do normally and what to do if a common mis-hap occurred. Why was there a sudden surprise? Equally, the gotcha of pushing the wrong TOGA button is not a first and I'd have expected the captain as PF to be extra alert to where his fingers were close to DH. Does AF fly LVO as a monitored approach? Can the F/O call G/A above DH? Do not get diverted by a discussion about a 20' DH. It is irrelevant to this. I haven't read the report, but from the details given in the first post the incident was created by some strange behaviour above DH. Without knowing the SOP's in AF we can not make reasoned comments. Let's keep any comments to relevant facts.
This incident begs several questions – with hindsight.
Why GA. What is the procedural rationale for GA if some capability remains; does it assume only the worst case visibility? Similarly, would the procedure apply during a VMC practice approach? How are the procedures evaluated, taught, and reviewed?
Are the crew expected to manage such dilemmas?
If there have been similar inappropriate selections of AT disc opposed to GA, were there any safety reports, did the manufacturer know, was the design evaluated and approved with such actions considered? Assuming safety reports are submitted, who considers and acts on them?
Why didn’t the AP initially disengage with pilot overpower. Normally this is a certification requirement to prevent back-driving the trim, as in this incident. AP approach settings might use higher torques thus requiring more overpower force, but due to the proximity to the ground other monitors are normally provided, if so what, when, why not?
Perhaps the investigation should have asked these questions, also the others above.
The ASAGA study referred to in the report is at http://www.bea.aero/etudes/asaga/asaga.study.pdf
Highly recommended reading of Sections 3 Flight Crew Survey - Problems, 4 Simulation, and 6 Analysis, all of which identify opportunities for improving safety.
Why GA. What is the procedural rationale for GA if some capability remains; does it assume only the worst case visibility? Similarly, would the procedure apply during a VMC practice approach? How are the procedures evaluated, taught, and reviewed?
Are the crew expected to manage such dilemmas?
If there have been similar inappropriate selections of AT disc opposed to GA, were there any safety reports, did the manufacturer know, was the design evaluated and approved with such actions considered? Assuming safety reports are submitted, who considers and acts on them?
Why didn’t the AP initially disengage with pilot overpower. Normally this is a certification requirement to prevent back-driving the trim, as in this incident. AP approach settings might use higher torques thus requiring more overpower force, but due to the proximity to the ground other monitors are normally provided, if so what, when, why not?
Perhaps the investigation should have asked these questions, also the others above.
The ASAGA study referred to in the report is at http://www.bea.aero/etudes/asaga/asaga.study.pdf
Highly recommended reading of Sections 3 Flight Crew Survey - Problems, 4 Simulation, and 6 Analysis, all of which identify opportunities for improving safety.
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Originally Posted by PEI_3721
Why didn’t the AP initially disengage with pilot overpower. Normally this is a certification requirement to prevent back-driving the trim, as in this incident.
There was no trim back-driving, the AP kept the aircraft on the ILS centrelines and applied a nose-down input on the THS as speed was increasing. Most probably FD were centered.
To me, a more informative call from the relief pilot after the amber warning could have been "NO LAND3" to which the PNF could have confirmed "LAND2" FMA indication and the PF who was visual "CONTACT - CONTINUE"
Not being visual at that time, and following AF procedures, the PF would have called "GO AROUND" and execute it.
Originally Posted by mightyauster
Yes, the yokes are mechanically linked, but there is a "break out" mechanism on the torque tube between them, so it is possible to force the yokes in opposite directions. There are pitch transducers on the bottom of each yoke, so the DFDR will pick up the position of each yoke.
CONF, I can appreciate that there would not be any trim-follow-up (as in manual flight) whist the AP was engaged. However from page 1 of the report, with the AP engaged (9 29 50) back stick appeared to result in nose down THS, possibly due to an autopilot generated trim demand to balance the opposing stick input.
The AP was still attempting to follow the ILS, but the mechanism of control had to balance the computed demand for the flight path with that of the disturbing demand of nose up stick input. Thus THS movement opposed the stick input and the AP managed a semblance of GS control.
Following the AP disengagement the aircraft was out-of-trim nose down, thus a tendency for nose down pitch until both pilots applied back stick. Presumably thereafter in manual flight there was some manual trim-follow-up.
There is still no explanation as to why the an opposing stick input (fighting the AP) at such a low altitude did not result in AP disengagement or provide a further alert in order to avoid a hazardous out-of-trim condition.
In systems where the AP design requires a higher force before disengaging then a combination of force-duration may be used, but again in this situation with a low force, the duration appeared unacceptably long for the low altitude.
The AP was still attempting to follow the ILS, but the mechanism of control had to balance the computed demand for the flight path with that of the disturbing demand of nose up stick input. Thus THS movement opposed the stick input and the AP managed a semblance of GS control.
Following the AP disengagement the aircraft was out-of-trim nose down, thus a tendency for nose down pitch until both pilots applied back stick. Presumably thereafter in manual flight there was some manual trim-follow-up.
There is still no explanation as to why the an opposing stick input (fighting the AP) at such a low altitude did not result in AP disengagement or provide a further alert in order to avoid a hazardous out-of-trim condition.
In systems where the AP design requires a higher force before disengaging then a combination of force-duration may be used, but again in this situation with a low force, the duration appeared unacceptably long for the low altitude.
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We read many accident reports where the observer or PM have said nothing.
Well done that man for spotting and shouting it out repeatedly. I'm sure it saved a lot more than 63ft.
Air France
Well done that man for spotting and shouting it out repeatedly. I'm sure it saved a lot more than 63ft.
Air France
Thus THS movement opposed the stick input and the AP managed a semblance of GS control.
Stretching memory back to my pre-Airbus-FBW days on several types, including the A310, I'm sure that it was normal for the AP to use autotrim to combat any yoke displacement by the pilot.
Thank you, Chris. Point being, I presume, to maintain last ordered/selected state or performance. If pilot is to fly it by hand AP disconnect would be a usual first step. Do I have that right?
Since there are various models and schemes, maybe this question isn't precise enough.
Since there are various models and schemes, maybe this question isn't precise enough.
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Originally Posted by PEI_3721
CONF, I can appreciate that there would not be any trim-follow-up (as in manual flight) whist the AP was engaged. However from page 1 of the report, with the AP engaged (9 29 50) back stick appeared to result in nose down THS, possibly due to an autopilot generated trim demand to balance the opposing stick input.
Quote from Lonewolf_50:
"Point being, I presume, to maintain last ordered/selected state or performance. If pilot is to fly it by hand AP disconnect would be a usual first step. Do I have that right?"
Definitely. Trying to override the AP is a no-no. If it's not doing what you want, you must disengage it. **
I infer that this PF must have thought that (a) he had operated the TOGA switches and/or (b) he had already disengaged the AP (he had, of course, only disconnected the A/THR). Meanwhile, the autotrim was countering his gentle pull-up by down-trimming the HS by 1.65 deg in 6 seconds.
Quote from CONF_iture:
"So we don't have a similar appreciation of the situation, as thrust increase and its pitch up effect + speed increase alone justify the THS nose down movement to properly trim for the negative pitch necessary for the aircraft to follow the GS."
Quite. Perhaps a B777 pilot will also tell us what the HS would normally have been doing if the go-around had been conducted properly - with or without AP? Experience on other big twins with under-slung engines suggests that down-trimming is normally required to counteract the thrust increase AND the partial retraction of the flaps. So maybe the failure of the a/c to rotate to a go-around pitch when the PNF pulled hard enough to disconnect the AP was caused purely by the PF's unexplained pushing on the yoke.
In terms of hours, this was a very experienced crew - both in terms of total hours, and hours on type...
** Detractors of Airbus-FBW should note that, with no AP connection to/from the sidesticks, the action of pulling a sidestick back would have no effect on the AP or autotrim until it was pulled hard enough to disengage the AP. At AP disconnect, the THS would still be trimmed for the vertical profile the AP was last conducting.
"Point being, I presume, to maintain last ordered/selected state or performance. If pilot is to fly it by hand AP disconnect would be a usual first step. Do I have that right?"
Definitely. Trying to override the AP is a no-no. If it's not doing what you want, you must disengage it. **
I infer that this PF must have thought that (a) he had operated the TOGA switches and/or (b) he had already disengaged the AP (he had, of course, only disconnected the A/THR). Meanwhile, the autotrim was countering his gentle pull-up by down-trimming the HS by 1.65 deg in 6 seconds.
Quote from CONF_iture:
"So we don't have a similar appreciation of the situation, as thrust increase and its pitch up effect + speed increase alone justify the THS nose down movement to properly trim for the negative pitch necessary for the aircraft to follow the GS."
Quite. Perhaps a B777 pilot will also tell us what the HS would normally have been doing if the go-around had been conducted properly - with or without AP? Experience on other big twins with under-slung engines suggests that down-trimming is normally required to counteract the thrust increase AND the partial retraction of the flaps. So maybe the failure of the a/c to rotate to a go-around pitch when the PNF pulled hard enough to disconnect the AP was caused purely by the PF's unexplained pushing on the yoke.
In terms of hours, this was a very experienced crew - both in terms of total hours, and hours on type...
** Detractors of Airbus-FBW should note that, with no AP connection to/from the sidesticks, the action of pulling a sidestick back would have no effect on the AP or autotrim until it was pulled hard enough to disengage the AP. At AP disconnect, the THS would still be trimmed for the vertical profile the AP was last conducting.
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Originally Posted by Chris Scott
Stretching memory back to my pre-Airbus-FBW days on several types, including the A310, I'm sure that it was normal for the AP to use autotrim to combat any yoke displacement by the pilot.
In 94, after Nogoya, Airbus made mandatory the Flight Control Computer modification to allow AP disengagement through manual controls input.
So maybe the failure of the a/c to rotate to a go-around pitch when the PNF pulled hard enough to disconnect the AP was caused purely by the PF's unexplained pushing on the yoke.
Only later on the CPT has been unexplainably pushing on his controls.
Detractors of Airbus-FBW should note that, with no AP connection to/from the sidesticks, the action of pulling a sidestick back would have no effect on the AP or autotrim until it was pulled hard enough to disengage the AP. At AP disconnect, the THS would still be trimmed for the vertical profile the AP was last conducting.
Actually, it would be very interesting to know if the too weak action of the CPT on the controls to disconnect AP, had any effect on the THS ... ?
It is a question that Boeing could answer.
Quite. Perhaps a B777 pilot will also tell us what the HS would normally have been doing if the go-around had been conducted properly - with or without AP? Experience on other big twins with under-slung engines suggests that down-trimming is normally required to counteract the thrust increase AND the partial retraction of the flaps. So maybe the failure of the a/c to rotate to a go-around pitch when the PNF pulled hard enough to disconnect the AP was caused purely by the PF's unexplained pushing on the yoke.
From the FCOM about autopilot disconnect force.
When an override force sufficient to move the control column, control wheel, or rudder pedals (LAND 2 of LAND 3 annunciated) is applied, the fly-by-wire flight control system will detect a difference between the cockpit controls and its own estimate of the expected positions, and will force a disconnect of the autopilot. After the autopilot is disconnected, the control system will transition the control surface commands from those of the autopilot to those of the flight crew
From what I understood the PF disconnected the A/T, applied full power whilst still going down the GS because the TOGA SWITCHES weren't pushed which would have put the aircraft in a 1500fpm climb. I'm not sure exactly how much force is necessary to disconnect the A/P but it could have been exaggerated by the increasing SPD.
The PF could have still hit the TOGA switches which would have forced the aircraft to climb as he had already applied full power although at a higher pitch angle. Alternatively he could have just used the A/P disconnect button on the control Yolk but like most people I suspect he thought the A/P was disconnected.
Quotes from CONF_iture:
"It was "normal" but unwise."
Normal for the AP, not for the PF, which is why I described it later as "a no-no"!
"This is not what happened. AP disconnected when both were pulling on their yoke. Only later on the CPT has been unexplainably pushing on his controls."
Quite. You might consider reading what I write more carefully? After the AP disconnected, the PNF's attempts to pitch the a/c up seem to have been hindered by the PF's pushing forward. One wonders if the PF might have been anticipating an over-rotation that never happened.
"Actually, it would be very interesting to know if the too weak action of the CPT on the controls to disconnect AP, had any effect on the THS ... ?"
That was what I suggested, but you argued quite correctly that to maintain the descent the HS would need to compensate for TOGA even without pilot interference.
Quote from flyhardmo:
"The 777 FBW will auto trim the HS during any power or config changes so you don't feel the trim changes."
That sounds straight out of a sales brochure! My question was: does it have to trim forward during a normal go-around, and - if so - roughly how much? In other words, did the fact that it had trimmed 1.65 deg forward before the AP disconnected subsequently make the pilots' manual rotation to a go-around pitch more difficult, or would they have needed to trim forward anyway?
"It was "normal" but unwise."
Normal for the AP, not for the PF, which is why I described it later as "a no-no"!
"This is not what happened. AP disconnected when both were pulling on their yoke. Only later on the CPT has been unexplainably pushing on his controls."
Quite. You might consider reading what I write more carefully? After the AP disconnected, the PNF's attempts to pitch the a/c up seem to have been hindered by the PF's pushing forward. One wonders if the PF might have been anticipating an over-rotation that never happened.
"Actually, it would be very interesting to know if the too weak action of the CPT on the controls to disconnect AP, had any effect on the THS ... ?"
That was what I suggested, but you argued quite correctly that to maintain the descent the HS would need to compensate for TOGA even without pilot interference.
Quote from flyhardmo:
"The 777 FBW will auto trim the HS during any power or config changes so you don't feel the trim changes."
That sounds straight out of a sales brochure! My question was: does it have to trim forward during a normal go-around, and - if so - roughly how much? In other words, did the fact that it had trimmed 1.65 deg forward before the AP disconnected subsequently make the pilots' manual rotation to a go-around pitch more difficult, or would they have needed to trim forward anyway?