AF 447 Thread No. 9
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes
on
0 Posts
OK465:
Thank you for your post #1392. I understand most of what you are saying, except when you say "a more relaxed SS input". A valid experiment would compare the two cases at exactly the same entry conditions and exactly the same pilot inputs. On 'theoretical grounds' I remain convinced that the resulting airplane trajectories would be identical up to the point where the elevator reaches the stop.
Thank you for your post #1392. I understand most of what you are saying, except when you say "a more relaxed SS input". A valid experiment would compare the two cases at exactly the same entry conditions and exactly the same pilot inputs. On 'theoretical grounds' I remain convinced that the resulting airplane trajectories would be identical up to the point where the elevator reaches the stop.
Join Date: Jan 2008
Location: uk
Posts: 857
Likes: 0
Received 0 Likes
on
0 Posts
Sidestick force is not relevant because you could have let it return to neutral and it would do the same.
THS is not relevant either, until you reach elevator limit, because the control feedback loops will simply command elevator deflection to achieve the path. If the THS helps then they will use less elevator, if not then they will use more. None of that changes sidestick force as there is no feedback.
A simulator experiment would clearly point the difference.
Trimming in a stall is an unknown procedure. It is dangerous stuff.
Trimming in stall recovery (if that's what you mean) damn well should be part of the procedure (if it's got to the point that pilots need a SOP for stall recovery
) and definitely should not be unknown. Failure to trim in stall (and approach to) recovery has killed or nearly killed a lot of people, on bus and other types.
We need to ask Airbus why they think differently.
As the BEA avoids asking the tough questions, we need to do it.
As the BEA avoids asking the tough questions, we need to do it.
If BEA find something relevant but then fail to ask the tough questions of the mfr / regulator then you might validly criticise [actually I think they have on at least one point, but no ones really picked up on it here yet...].
You might also disagree with their conclusions, just as some think that their conclusion that the fin stayed attached is wrong (or at least not sufficiently investigated).
But what you are doing is the same as criticising BEA for not asking hard questions about the composite fin and its attachments - there might well be hard and interesting questions still to be asked in that area, but they aren't for this report because they didn't cause this accident.
Join Date: Jan 2008
Location: uk
Posts: 857
Likes: 0
Received 0 Likes
on
0 Posts
I need to borrow the formula of HN39 here :
What a strange statement coming from you !
Dozy, you keep coming back on how crews have been pulling back on controls all the way during stalls, but Airbus 'simply never countenanced the idea that a pilot would pull into a stall, keep pulling through the stall warning and pull *again* once the stall was established'.
What a strange statement coming from you !
Dozy, you keep coming back on how crews have been pulling back on controls all the way during stalls, but Airbus 'simply never countenanced the idea that a pilot would pull into a stall, keep pulling through the stall warning and pull *again* once the stall was established'.
Alternate laws are a failure condition, and 447 was several failure conditions down to the point that the protections were gone. At that point AB system designers didn't lose sight of the possible pilot behaviour, just that without valid airdata they can't build a system to help.
I understand most of what you are saying, except when you say "a more relaxed SS input". A valid experiment would compare the two cases at exactly the same entry conditions and exactly the same pilot inputs.
With exactly the same entry condition, as a practical matter, I don't think maintaining identical trajectories could be accomplished with 'exactly the same pilot inputs' to the elevator limits.
I understand what you're saying, that in ALT LAW with a somehow fixed THS setting, the FCS should 'theoretically' reposition the elevator as necessary, even hands off, to maintain the flight path up to the point the elevator reaches 'full travel'.
In practice, in ALT LAW, if the THS is somehow stopped at any position, when further movement would be commanded, the FCPC treats this as a jammed stab and will only exercise about 1/2 of the remaining elevator movement automatically, leaving the pilot about 1/2 of the elevator movement for manual control.
And of course to make the comparison in DIRECT LAW (non Nz) requires a whole different series of pilot inputs.
So I see what you're saying. I guess it would be correct if one considered the limit of elevator travel to be 1/2 travel.
FCPC's are wonderful things.
Join Date: Jan 2008
Location: uk
Posts: 857
Likes: 0
Received 0 Likes
on
0 Posts
OK465:
Thank you for your post #1392. I understand most of what you are saying, except when you say "a more relaxed SS input". A valid experiment would compare the two cases at exactly the same entry conditions and exactly the same pilot inputs. On 'theoretical grounds' I remain convinced that the resulting airplane trajectories would be identical up to the point where the elevator reaches the stop.
Thank you for your post #1392. I understand most of what you are saying, except when you say "a more relaxed SS input". A valid experiment would compare the two cases at exactly the same entry conditions and exactly the same pilot inputs. On 'theoretical grounds' I remain convinced that the resulting airplane trajectories would be identical up to the point where the elevator reaches the stop.
The comparison should be: pitch-alternate law with normal THS behaviour vs. pitch-alternate law with 3deg THS limit. With same sidestick inputs, is the trajectory the same (up to elevator stops) ?
CONF - is that what you are saying you have done in SIM and if so, how ?
Join Date: Jan 2005
Location: W of 30W
Posts: 1,916
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by IF789
That flys in the face of everything published about Airbus C* control law.
DIRECT LAW all the way since data are diagnotized as unreliable.
Why keep trying to patch on dubious data ?
Keep it simple and straightforward - No ambiguity.
As said earlier, protections and and autotrim can well wait for the next flight, what's the urgency ?
Originally Posted by IF789
Trimming in stall recovery (if that's what you mean)
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes
on
0 Posts
The fundamental aspect of manual control as it applies to the FBW Airbus flight deck is that the pilot makes inputs, observes behaviour and then corrects if necessary. Slamming the stick against the backstop and holding it there runs counter to this methodology no matter what law you're in.
Now - first rule of Alternate is that there are no hard protections. If the AF447 PF had heard the PNF's call of "Alternate Law" he had no business making inputs that aggressively.
In this case, what you're glossing over is that while autotrim in Alternate Law may have extended the duration of the stall if the correct recovery action had been taken, the fact is that autotrim will *help you recover* from stall by the simple action of pushing the sidestick forward and holding it there.
You're also avoiding the fact that holding the stick back like that at cruise is a thoroughly inappropriate response no matter what you're flying.
Last edited by DozyWannabe; 17th Aug 2012 at 18:10.
Join Date: Feb 2009
Location: Cardiff
Age: 48
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
Sorry
Yes, inexplicably I did get the flight number wrong. Sorry about that. As I can't possibly live this down I'm now withdrawing from Pprune.
Last edited by korrol; 17th Aug 2012 at 18:19. Reason: typo
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes
on
0 Posts
korrol
Yes, inexplicably I did get the flight number wrong
Yes, inexplicably I did get the flight number wrong
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes
on
0 Posts
OK465
In practice, in ALT LAW, if the THS is somehow stopped at any position, when further movement would be commanded, the FCPC treats this as a jammed stab and will only exercise about 1/2 of the remaining elevator movement automatically, leaving the pilot about 1/2 of the elevator movement for manual control.
In practice, in ALT LAW, if the THS is somehow stopped at any position, when further movement would be commanded, the FCPC treats this as a jammed stab and will only exercise about 1/2 of the remaining elevator movement automatically, leaving the pilot about 1/2 of the elevator movement for manual control.
Join Date: Jan 2005
Location: W of 30W
Posts: 1,916
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Dozy
Except that Direct Law throws the crew into a situation where the aircraft handles differently in *every axis* compared to what they are used to, which would likely be more risky than the current design.
You're also avoiding the fact that holding the stick back like that at cruise is a thoroughly inappropriate response no matter what you're flying.
It is not before the THS was at 13 deg that 'the stick was hold back like that'.
And thank you for reminding that holding back a flight control is inappropriate. I'm sure the PNF and the CPT would have loved to know about it when the PF was doing it ...
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes
on
0 Posts
That argument might hold water if every (or even a majority of) line pilot(s) on here agreed with you, but they don't.
It should never have been held back at all!
The attitude on the ADI would have been a pretty big hint.
It is not before the THS was at 13 deg that 'the stick was hold back like that'.
And thank you for reminding that holding back a flight control is inappropriate. I'm sure the PNF and the CPT would have loved to know about it when the PF was doing it ...
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes
on
0 Posts
CONF iture
After all the debate over the unknown position of the other pilots SS, I now suspect that you would be happy to accept the "Iron Cross" display of the SS position on the PFD following an A/P disconnect and law reversion in flight mode.
After all the debate over the unknown position of the other pilots SS, I now suspect that you would be happy to accept the "Iron Cross" display of the SS position on the PFD following an A/P disconnect and law reversion in flight mode.
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes
on
0 Posts
I'm well aware of the need for a powerful THS, as I suspect most every other pilot is also aware and that is PRECISELY the reason I find it disturbing that the Airbus THS operates without pilot awareness so much of the time. As this trim discussion continues, I find myself questioning the system more and more.
I've thought about what took place after AP/AT disconnect on AF447. It quickly became an unorganized experiment in flight ending with the comment "We've tried everything". In reality it didn't have to be this way.
From an earlier PJ2 posting in the AF447 Final Crew Conversation:
In my opinion as a (retired) A330 captain, the "safe conduct of the flight" was never an issue with regard to AF447, (and wasn't with all other similar UAS events).
However, "safe conduct" is a subjective, not objective decision-point in a critical drill/checklist and I think that is a problem that can lead the crew into an inappropriate and unnecessarily quick response.
A loss of airspeed indication is not an emergency, nor was immediate action required, especially of kind executed here which was uncoordinated, unilateral actions (meaning the absence of the use of SOPs) by the PF which went unchallenged by the PNF.
As discussed previously, all the crew had to do was to maintain pitch attitude and power setting as per the UAS QRH checklist while the abnormality was announced by the PF and the QRH called for so that precise pitch and power settings could be determined. There was no need to set a different pitch attitude at all.
I think this is partly 1) a drill/checklist problem, 2) partly a training problem and 3) partly a cockpit discipline problem.
1) the drill/checklist is poorly-written and confusing as to correct response, 2) their UAS training was done quite some time prior to this event on an A320 simulator, with the UAS occuring right after takeoff (requiring TOGA/15°) and not at cruise altitude which didn't require any action at all as the "safe conduct of the flight" was not in question, and 3) the cockpit discipline matter has been thoroughly discussed but there was a leadership-followership issue which was (and still is) a problem when two F/Os are in command of the flight, and the captain did not address how drills would be handled.
However, "safe conduct" is a subjective, not objective decision-point in a critical drill/checklist and I think that is a problem that can lead the crew into an inappropriate and unnecessarily quick response.
A loss of airspeed indication is not an emergency, nor was immediate action required, especially of kind executed here which was uncoordinated, unilateral actions (meaning the absence of the use of SOPs) by the PF which went unchallenged by the PNF.
As discussed previously, all the crew had to do was to maintain pitch attitude and power setting as per the UAS QRH checklist while the abnormality was announced by the PF and the QRH called for so that precise pitch and power settings could be determined. There was no need to set a different pitch attitude at all.
I think this is partly 1) a drill/checklist problem, 2) partly a training problem and 3) partly a cockpit discipline problem.
1) the drill/checklist is poorly-written and confusing as to correct response, 2) their UAS training was done quite some time prior to this event on an A320 simulator, with the UAS occuring right after takeoff (requiring TOGA/15°) and not at cruise altitude which didn't require any action at all as the "safe conduct of the flight" was not in question, and 3) the cockpit discipline matter has been thoroughly discussed but there was a leadership-followership issue which was (and still is) a problem when two F/Os are in command of the flight, and the captain did not address how drills would be handled.
Aside from this on a more general note, there was an interesting revised book requested by the FAA and assembled by Airbus, Boeing, Flightsafety and various participating airlines and others. It issued prior to the AF447 accident, AF was not a participating airline but distribution of this to their flight crews could have been helpful. If you have not seen it, you can view it by going here:
http://flightsafety.org/files/AP_UpsetRecovery_Book.pdf
Join Date: Mar 2009
Location: Inside
Posts: 285
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by mm43
the cabin pressure in an A330 on a flight of greater than 2.5 hours duration is set at 7,350 feet.
Join Date: Jan 2005
Location: W of 30W
Posts: 1,916
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by mm43
After all the debate over the unknown position of the other pilots SS, I now suspect that you would be happy to accept the "Iron Cross" display of the SS position on the PFD following an A/P disconnect and law reversion in flight mode.
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes
on
0 Posts
And the period during the zoom climb where it was way in excess of what would normally be accepted? In any case, if the ADI is showing evidence that pitch stability is a problem then stall definitely moves towards the head of the table as far as probable reasons go.