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-   -   Habsheim (https://www.pprune.org/tech-log/528034-habsheim.html)

Chris Scott 9th Nov 2013 19:15

Memory (off-topic) [This post has been copied from "AF447 Thread No. 11"]
 
Quote from Conf_iture, re the A320 Habsheim accident of 1988:
"Sorry Chris but I just can't understand your thinking here as part of the procedure to present the Airbus at high AoA is specifically to inhibit A/THR to prevent Alpha Floor to spoil the demonstration.
How can you suggest the guy was waiting for Alpha-Floor to kick in when his initial intention was to prevent it to interfere in the first place ?"


My off-topic reference to Habsheim was merely to illustrate that speed greater than M0.53 is not the only inhibition criterion for Alpha-Floor.
What you say suggests the game plan was even more cavalier than I remembered, and my memory of the tortuous, much-criticised investigation has faded.

That accident was 25 years ago, in our first summer of A320 ops. We fellow A320 pilots were naturally riveted by the excellent camcorder footage of the a/c descending gently into the treetops as the engines spooled up. Much speculation followed, but it was clear to us that the a/c had stabilised safely at Alpha-MAX, but lacked enough thrust to maintain its height.

I assumed the plan had been to stabilize at about Alpha-Prot, maintain height at that speed by increase of manual thrust while passing in front of the crowd, and then go-around. It never occurred to me at the time that the crew would have been reckless enough to attempt to stabilise at Alpha-MAX, as you seem to believe, disabling Alpha-Floor to enable that. I presumed that Alpha-Floor was being retained as a back-up, but that its inhibition below a certain height had been overlooked.

CONF iture 10th Nov 2013 03:52

Chris, more than anything, why Habsheim has not a thread on its own ...?


Originally Posted by Chris Scott
I assumed the plan had been to stabilize at about Alpha-Prot, maintain height at that speed by increase of manual thrust while passing in front of the crowd, and then go-around. It never occurred to me at the time that the crew would have been reckless enough to attempt to stabilise at Alpha-MAX, as you seem to believe, disabling Alpha-Floor to enable that.

Taking advantage of the electronics it is much easier to stabilize at Alpha-Max, A/THR system being disconnected for the remainder of the flight, than trying to find Alpha-Prot without triggering Alpha-Floor.

DozyWannabe 10th Nov 2013 15:55


Originally Posted by vilas (Post 8143271)
I am sorry but it appears that you have completely misunderstood normal law and protections.

As it happens I'm pretty au fait with it. I did however phrase it somewhat badly - probably my fault for posting under the influence. I wasn't saying that protection *causes* the nose to come up, I was saying that when the protections are active, the pitch angle will invariably be nose-high, therefore putting the nose down to reduce the AoA - and disengage the protection - should be a fairly intuitive action for a pilot.

@CONF - I've invited you on several occasions to start your own Habsheim thread in AH&N (the logical place to have it, as the incident is over two decades old) - but you have not as yet done so.

@Chris - I think we do know that Alpha Floor was not a consideration for the pilot of AF296, as he *disabled* A/THR (and thus A. Floor) by holding down the disconnect switches to perform the flypast.

CONF iture 18th Nov 2013 09:19

Habsheim
 

Originally Posted by john_tullamarine
Folks,
We've had a few complaints about introducing Habsheim in this thread. If folks see a need to discuss, please raise a second thread to keep the two easier to follow.

John,
It is not clear why pprune did not let me start a thread on Habsheim in the past, but as the offer is now formulated, sure I can proceed.

There's a lot to say on the technical side, stuff that may help to understand how the Airbus works.

Maybe you would like to transfer here what we wrote lately regarding Habsheim in the AF 447 Thread No. 11

john_tullamarine 18th Nov 2013 09:44

Can't speak to the modding history but I guess so long as we keep the thread on a tech mindset and don't get into any operator or personality aggro then things should go fine.

Connection is too slow at the moment to move the posts .. will finish that task tomorrow.

390cruise 18th Nov 2013 11:32

100 ft. Rad Alt
 
Guys,
My understanding was that this crew intended to slow towards alpha protection during the fly past as some others had done at previous displays.
Unaware the others stayed above 100ft rad alt to ensure protection was available.Below 100ft they awaited for this now inhibited system.

roulishollandais 19th Nov 2013 20:25

Welcome!
Could we build a list of what changed on A320 since the day before Habsheim?

CONF iture 21st Nov 2013 15:41


Originally Posted by john_tullamarine
Connection is too slow at the moment to move the posts .. will finish that task tomorrow.

John,
Here are the posts that ideally could be moved to the present thread :
  1. 8th Nov 2013, 00:23 #700 Chris Scott
  2. 8th Nov 2013, 01:00 #702 CONF iture
  3. 8th Nov 2013, 19:18 #709 DozyWannabe
  4. 9th Nov 2013, 01:01 #712 Chris Scott
  5. 9th Nov 2013, 11:13 #716 CONF iture
  6. 9th Nov 2013, 19:15 #727 Chris Scott
  7. 10th Nov 2013, 03:52 #732 CONF iture
  8. 10th Nov 2013, 15:55 #737 DozyWannabe
  9. 11th Nov 2013, 10:42 #746 CONF iture
  10. 11th Nov 2013, 13:11 #747 DozyWannabe
  11. 11th Nov 2013, 14:05 #748 Winnerhofer
  12. 11th Nov 2013, 17:37 #751 CONF iture
  13. 11th Nov 2013, 17:49 #752 Owain Glyndwr
  14. 11th Nov 2013, 18:48 #753 CONF iture
  15. 11th Nov 2013, 20:10 #754 Owain Glyndwr
  16. 12th Nov 2013, 07:35 #755 CONF iture
  17. 12th Nov 2013, 08:22 #756 Owain Glyndwr
  18. 12th Nov 2013, 14:11 #759 DozyWannabe
  19. 13th Nov 2013, 05:57 #775 CONF iture
  20. 13th Nov 2013, 08:12 #776 Owain Glyndwr
  21. 13th Nov 2013, 08:18 #777 Clandestino
  22. 13th Nov 2013, 11:29 #778 CONF iture
  23. 13th Nov 2013, 19:19 #784 Chris Scott
  24. 14th Nov 2013, 05:44 #786 CONF iture
  25. 14th Nov 2013, 10:16 #787 aircrashesandmiracle
  26. 14th Nov 2013, 16:29 #789 DozyWannabe
  27. 14th Nov 2013, 22:10 #790 Winnerhofer
  28. 15th Nov 2013, 14:21 #791 CONF iture
  29. 15th Nov 2013, 16:45 #792 DozyWannabe
  30. 15th Nov 2013, 23:06 #793 CONF iture
  31. 16th Nov 2013, 00:36 #795 DozyWannabe
  32. 16th Nov 2013, 15:01 #802 CONF iture
  33. 17th Nov 2013, 19:09 #825 DozyWannabe
  34. 17th Nov 2013, 19:37 #826 jcjeant
  35. 17th Nov 2013, 20:46 #827 john_tullamarine

For clarity, if possible, would be nice to keep that one on top.

CONF iture 26th Nov 2013 18:34

... Then maybe I'll resume from where we left :
#825 from Dozy


Because to the best of my knowledge nothing in the documentation ever implied that Alpha Prot, or even Alpha Max, were the equivalent of Critical AoA.
And what is it supposed to mean ... ?


I'm not "spreading disinformation", and I challenge you to prove anything I've said recently to be wrong.
No need to go far ... http://www.pprune.org/8144775-post737.html

I think we do know that Alpha Floor was not a consideration for the pilot of AF296, as he *disabled* A/THR (and thus A. Floor) by holding down the disconnect switches to perform the flypast.

CONF iture 28th Nov 2013 12:08


Originally Posted by 390cruise
Below 100ft they awaited for this now inhibited system.

The AoA protection is not inhibited, only Alpha-Floor is, and Alpha-Floor has to be avoided for this type of demonstration.

CONF iture 10th Dec 2013 03:51

http://www.pprune.org/8197677-post10.html

Originally Posted by SMOC
the plane didn't climb over the trees because it was already at max alpha for the slow fly-by

No it was not.
The plane refused to deliver alpha max, it kept 2.5 deg short of it.
Did the BEA Report actually mention that the airplane was flying at alpha max ... ?

john_tullamarine 10th Dec 2013 05:37

Re moving posts, several folks have requested that their posts not be moved so I will need to proceed with consideration as time permits.

awblain 10th Dec 2013 08:00

2.5 degrees above alpha max?
 

The plane refused to deliver alpha max, it kept 2.5 deg short of it.
I'm genuinely ignorant about the details of what the aircraft would deliver in different circumstances.

Did it deliver alpha that was 2.5 deg less than alpha max in order to avoid pushing too close to the limit? I.e. is that 2.5 degrees a safety margin in the software?

I can find the BEA report in French, and can't translate accurately enough to tell.

I did find an interesting site where there's photos of someone carrying away the blackboxes - AirDisaster.Com: Investigations: Air France 296. The site claims that the white stripes on the DFDR box in pictures No. 3 and No. 4 are different, when in fact they look identical to me.

BOAC 10th Dec 2013 08:12

Re moving posts, John, in my day here mods could 'copy' posts to a new thread. It takes a few minutes........:p

CONF iture 10th Dec 2013 16:41


Originally Posted by awblain
Did it deliver alpha that was 2.5 deg less than alpha max in order to avoid pushing too close to the limit? I.e. is that 2.5 degrees a safety margin in the software?

The margin is already in alpha max, that's why alpha max has not been set to alpha stall. It was the Airbus responsibility to detail why, under a given altitude ... (?), and contrary to what the documentation says, alpha max cannot be delivered despite the pilot request.
It was the BEA duty to mention such characteristic.

DozyWannabe 10th Dec 2013 20:26


Originally Posted by awblain (Post 8197998)
I did find an interesting site where there's photos of someone carrying away the blackboxes...

Regardless of what the site says, no-one has ever confirmed that the flight recorder cases in that photo were the ones recovered from the aircraft. It's possible that those were just dummy cases shown to the recovery workers so that they'd know what to look for.

Alpha Max is an internal designation - it is not a universally recognised variable. Airbus never claimed that Alpha Prot would deliver a max AoA equivalent to the edge of stall, just that it would maintain an AoA short of stall while providing as much of the demanded pitch attitude within the safe boundary as it could.

Chris Scott 10th Dec 2013 21:11

This thread
 
Quote from john_tullamarine:
Re moving posts, several folks have requested that their posts not be moved so I will need to proceed with consideration as time permits.

Quote from BOAC:
Re moving posts, John, in my day here mods could 'copy' posts to a new thread.

I've no objection to any posts of mine that may have some relevance to Habsheim being duplicated here, although I'm not sure there are any. Any editing could result in comments finding themselves out of context. Would also prefer them not to be deleted or edited in their original threads, for the same reason.

As for finding myself involuntarily and nominally the original poster of a thread on the infamous Habsheim accident, I am sanguine. However, it may be worth placing on record that it was not my idea, and I was not consulted.

:)

DozyWannabe 10th Dec 2013 21:19

Possibly a moderator annotation explaining why the thread was created and at whose request?

john_tullamarine 10th Dec 2013 22:55

Without going back into the history and dotting is and crossing ts ...

(a) the other thread saw some folk requesting the Habsheim discussion be calved into a separate thread - easy enough to sort out

(b) some folk have requested that they NOT be involved with the Habsheim thread - easy enough to sort out but requires a bit of care to honour the relevant undertakings in that regard

Nothing sinister anywhere along the way .. just trying to keep the maximum number of folks happy at the same time.

With this sort of exercise, I am not interested in any editing but Chris's comment on maintaining context is valid and not always easily sorted out.

DozyWannabe 10th Dec 2013 23:07

Understood John, and thanks for doing this!


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