AF 447 Search to resume (part2)

[DenisG]

Still, there remain many many questions unanswered, especially in regard to the ACARS and what the situation was on the flight deck accordingly.

NAV TCAS FAULT (2h 10m) and
FCPC2 (2CE2) WRG:ADIRU1 BUS ADR1-2 TO FCPC2 (2h 10m)

- disappearance of FPV incl. angle of attack

New info:
At 2 h 10 min 51 + 60 seconds
The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight.

[Lonewolf_50]

HN39, we seem to have a misunderstanding barrier issue here, in re the word tolerance. I am not suggesting you tolerate abrupt control motions as in "I'll put up with that, no problem" but am rather meaning "tolerance" in terms of fault tolerance, or what it does to you, as a pilot, when you have abrupt and uncommanded pitch inputs. How do you as a pilot respond to this sort of fault ... so it's more like fault tolerance. Sorry about that semantic ambiguity.

[takata]

Hi Poit,

Originally Posted by Poit

A little less information in the report than I expected, to be honest.

To be honest, I didn't expected more at this point from the BEA. They refrained to comment the facts. I'm feeling that they still have plenty to investigate before going further than those factual informations released. Such description is nonetheless useful rather than being left with those contradictory press leaks.

If they don't say what put the THS at this setting (where it was not until a while), it doesn't mean they don't have any idea about it but that it is not settled. They won't make any "guess". One may also suspect that if you are pitching up during a long time, the THS would also follow what you want, and if the pilot idea was to climb or to keep the nose up, then it may also have been settled thru the trim wheel.
For my part, what bother me particularly is that plenty of parameters are not recorded at all: only LH speed and stand-by, for example. This is not good if one want to fully understand this system logic.

[RetiredF4]

LandIT
THS nose up
I also am stunned.
Do we know who or what caused the THS to go to 13 deg and stay there. Surely this extreme setting is a major contributor to the disaster. If this was HAL then surely Airbus has some explaining to do. I think this is not the first time the THS on an Airbus in trouble has gone to a high setting and the crew didn't notice, or am I wrong?

In my F4 a runaway stabilator trim would have been the appropriate malfunction. It was not easy to recognize in altitude hold mode, but eyewatering once autopilot did disengage.
However in that case i would assume, that HAL was trimming until running out of ideas due to the wrong airspeed indications.

franzl

[Capn Bloggs]

I've never flown an airliner, so maybe there was something in the crew's insistance on maintaining a nose-up attitude that makes sense to those who have done, but from my flying experience that's tantamount to suicide when you're in a stall environment, with stall warnings sounding.

Probably because that's what we were all told to do: Minimise altitude loss, not stuff the bloody nose down until you get unstalled. Only recently has the emphasis been changed to the classic stall recovery: stuff the bloody nose down until you get unstalled then sort out the altitude loss!

Aircraft gives up on you, and you've never had to be violent with the aircraft before, especially at high altitude. You'd be a bit reluctant to do anything drastic, especially if you don't normally even "fly" the thing.

The crew will be blamed, but they were set up by the system.

[infrequentflyer789]

Originally Posted by LandIT

I also am stunned.
Do we know who or what caused the THS to go to 13 deg and stay there. Surely this extreme setting is a major contributor to the disaster. If this was HAL then surely Airbus has some explaining to do. I think this is not the first time the THS on an Airbus in trouble has gone to a high setting and the crew didn't notice, or am I wrong?

Not wrong - Perpignan crash. Autotrim put the THS high, in response to pilot input, and then autotrim dropped out - but the pilots never retrimmed manually (leaving them with no pitch autority).

However, this is not a FBW issue, nor just a Bus issue - this sequence:

• autotrim trims THS up
• a/c approaches stall
• autotrim drops out
• pilots fail to re-trim
• no pitch authority available to recover from stall

Is common to a number of incidents and fatal accidents now, and it's happening on non-FBW (eg. 737) planes as well.

Note: I am unclear as to why THS went up in this case, first reading of latest BEA document suggests it was in response to PF nose-up inputs, not HAL It's also not clear if autotrim ever dropped out (or stopped working) in this event.

[john_tullamarine]

Link to 447 thread #3