JD-EE

Lone - politicians tell the lawyers what they want in a law in response to their electorate's demands and trial lawyer campaign contributions.

- Enough OT....

wallybird7

MartinM

"I was not trying to blame the PF at this stage. I did not say hang him. All I try is to figure out what made him pull after disconnecting the AP. But obviously there is no real data around to get a conclusion on this.

Yes, maybe BEA will release at some point further details of the FDR and CVR. A reconstruction of the instrument situation would be interesting."

Everyone seems to be saying that the PF pulled the plane up. The only reference to that is that the elevator increased into a nose up trim condition.

What if a strong updraft pushed the plane up to 38,000 while at the same time the nose dropped. Then trim would autmatically apply in the opposite direction, to trim up.

We're not getting precise information on exactly when the icing occurred, and when the auto systems kicked off or on again.

Or what the pilots were saying at that same time.

Wild turbulent excursions create a lot of strange inputs that I question the auto-systems can cope with. Which is why they kicked off.

DozyWannabe

And this is not specific to Airbus aircraft CONF. The fact is that when you have pitot/static failure, all bets are off when it comes to warnings/indications and the crew must concentrate extremely hard to work out what's going on.

alf5071h

From a simplified description of the residual high-speed protection in alternate law:- “A nose up command is introduced any time the airplane exceeds VMO / MMO to keep the speed from increasing further, which CAN be overridden by the sidestick.”

Will the protection-generated nose up command result in (time delayed) trim movement, or is trim only activated by a sidestick input?

Is a fly-level stick command interpreted as an override of the protection command? I suspect not as how else will the protection work; thus does the sidestick have to be moved forward to effect the override?

Would the FDR differentiate between a protection-generated nose up command and that of the sidestick?

Are there any default values for VMO / MMO for failure or invalid airspeed / Mach inputs to the limit computations?

JD-EE

CONFiture, I tend to agree with you. Too many laws. Unless the control laws decay nicely with a tactile feedback signal via the stick it's really hard to keep all the "if" clauses together in your mind in a crisis.

PickyPerkins

I don't think Wainwright's talk mentioned AoA.

My main reason for thinking that Wainwright's talk might be of interest on this thread was (and is) his reference to the use of trim in upset recovery.

--- START EXTRACTS -----
Thus, for us (manufacturer's test pilots), an aircraft that is out-of-trim, for whatever reason, human or mechanical failure, should be re-trimmed. Whereas the airline instructors were against the use of trim .............

We spent a lot of time discussing the use of elevator trim, and we never reached agreement.

All the major US airlines were adamant on their policy to recover first using “primary controls” which excluded any reference to trimming. ...........

Again, a compromise was necessary ...............

And, the use of trim is not mentioned in the simplified lists of actions to be taken. .............
--- END EXTRACTS -------

So after two years of debate, the test pilots were forced into a "compromise" where although they considered the recovery sequence shoukd be:
first, trim the a/c --> then, regain flying speed --> finally, start recovering, in that order, the airline representitives refused to allow trim to appear at all in the short list of actions to be taken.

From some comments on this thread I gather that trim is still often not a priority action in airline upset recovery training.

Perhaps someone with recent experience can comment?

HazelNuts39

And the cosine of 61 degrees is 0.4848, so the longitudinal component of 151 kt is 73 knots?

HazelNuts39

In that case the airspeed would increase, and the total energy. That did not occur. Total energy decreased slightly until the stall, then dropped rapidly.

Ashling

Hi speed protection (Normal Law) cannot be overridden. The pitch up can be reduced, possably delaying recovery, but not overridden even with full forward stick. If you leave it alone to do its thing the altitude deviation will be no more than 700'. This is why Airbus advise against making pitch up commands during hi speed protection.

Importantly the autopilot disconnects on activation and if you pitch up strongly you can end up in AoA protection. Source Airbus Safety First Magazine.

Green-dot

Question 1:
What are the differences between Alternate 1 and alternate 2 laws regarding pitch? (Info below taken from an A330 Vacbi.)

Alternate 1:
The pitch attitude (Theta) protection is lost. High speed and stall protection are alternate.

Alternate 1A:
In addition the stall protection is lost.

Alternate 2:
The pitch attitude is lost and high speed and stall protection are alternate.
In addition the lateral normal law is lost and replaced by the lateral alternate law (roll direct and yaw alternate).

Alternate 2A:
In additition stall protection is lost.

Alternate 2B:
Pitch attitude, high speed, and stall protection are lost and the lateral normal law is replaced by lateral alternate law (bank angle protection lost).

With regards to "Pitch attitude is lost" in Alternate 2: Does this aggravate the situation perhaps in combination with a loss of- or unreliable pitch indication on the PFD (ADI portion) due to faulty/rejected ADIRU's? With the PF commanding a/c nose up, could he have been looking at an ADI telling him (erroneously) the a/c nose was pointing down?

Question 2:
Does the A330 FBW have a Flight Control System Self-test?

I remember way back in the 80's when I was a crewchief on the Viper. During launch, the pilot did pre-flight checks as I monitored launch procedures in concert with the pilot. One of them was the flight control self-test which was performed with assistance of the crewchief to monitor flight control surface deflections.

On one occasion the aircraft passed the flight control self-test as far as cockpit indications were concerned but I observed a jittering LH flaperon. I informed the pilot and he did a second self-test with the same results, the system passed the test but the jittering flaperon returned. After the sef-tests were completed, when the pilot moved the stick manually, the jittering was also observed as soon as the flaperon moved up or down from the neutral position. Obviously the flight was aborted and subsequent trouble shooting revealed a bad ISA (Integrated Servo Actuator). If I remember correctly a voting spool was the culprit.


Could the A330 FBW system have similar failures go undetected?

DJ77

Worst case is alarms that don't help.
May I add this to the debate:
14 CFR 25.207 (extract): "Once initiated, stall warning must continue until the angle of attack is reduced to approximately that at which stall warning began."

HazelNuts39

DJ77;

EADS A330 TCDS A.004 mentions two Special Conditions which may be relevant: SC F-1 Stalling and scheduled operating speeds, and SC F-5 Flight envelope protections.

The wording of the FCOM suggests that there is no stall warning in normal law. Alternate law is a low-probability failure condition in which an airplane is not required to meet all requirements that apply normally.

RetiredF4

17.th Performance and Operations Conference in Dubai May 2011

Interesting
- the emphasize on AOA in relation to stall
- the problems concerning destiction of approach to stall and already stalled
- the date of publishing May 2011 !!

Question? The title sounds funny. Would have expected something like

"update on stall avoidance & recovery procedure airbus"


Edit: Jusdt saw, that it is on the other thread in R+N, its really getting hard to keep track on two different threads. Sorry for that.

NigelOnDraft

HN39 My understanding is that Stall Warning is available in Normal Law - however, AoA protection means that you should not get to the AoA required to trigger it. Perpignan showed this where there was a Stall Warning in Normal Law (2(?) AoA probes frozen prevented Alpha protection, 3rd [unfrozen] AoA probe triggered the Stall Warning IIRC.

I would say that even if I am correct, this does not alter the substance of your post

rudderrudderrat

Hi retiredF4,

Thanks for the link to Stall Procedures Airbus May 11.

It is interesting to note that there is now a reference to stab trim.

"2 b) Nose down pitch trim…….………………………………………..As needed"

Mr Optimistic

When the flight control inputs were inappropriate, the stall warning ceased, and when they were appropriate, the stall warning reengaged …

Is there any circumstance were pushing the nose down can initiate or exacerbate a stall ?

auraflyer

I had a long post but after catching up on the huge backlog of posts that accrued while I was busy, much has been covered so will make some numbered points instead:

1. I've read this as a 2 stage process - AP off, an initial upset but the crew possibly thinks they have recovered it by 2:10:50 (when one calls for the captain). By this stage, PF has bled off a large amount of speed. Then a second event around 2:10:51 which causes a stall, apparently unrecovered until impact

2. At FL380, assuming actual airspeed was 215kt, and AoA 4 degrees, how far off stall were they as a function of airspeed? Could it be as simple as decaying airspeed at that point, hidden by UAS problems? (With underlying original cause, an unintentional climb, when trying to control roll, that lost them a large amount of airspeed?)

3. If the first two stall warnings were invalid, but the third one (which lasted a minute, and then reappeared briefly when nose was put down) was valid, could it have been disregarded initially because it followed two invalid ones? That is, crying wolf twice, followed by a true warning that was then ignored.

4. Could at least some of the nose-up commands (after the initial left/up) be due to the large divergence between AoA and pitch? If the plane started dropping hard vertically, causing very large AoA, but the ride was relatively smooth (see gums' posts a long while back), and pitch did not appear to be too high, then wouldn't nose-up commands appear logical? ie the pilot sees altitude dropping with nose apparently not too high, does not believe they are in a stall, and tries to lift it? Instead, consolidating the stall? All this even harder to detect at night, inside bad weather, no moon anyway. And with the effect of moving the THS back so far.

5. During the minute that followed the stall, ISIS airspeed recovers. Then after that minute, airspeeds go "invalid" and the third stall warning stops (having been going for a minute). While considered "invalid", was the airspeed either accurately measured <30 kts (or was it low, but further affected by the angle of incidence for pitots) and merely considered to be invalid because it was so low -- and in that case, we have a true (or nearly true) "invalid" airspeed following, and possibly confused by, original false reports caused by pitot problems? (ie again, the low airspeed was initially pitots crying wolf, but the next time it was for real because so much forward airspeed had been lost)

6. A design error that the (third) stall warning deactivated at unreliable airspeeds, only to reactivate once control started being reestablished (nose down, pushing airspeeds up above the "invalid" threshold, and leading to valid computations again) -- but with the net effect of making the correct input appear to be the wrong one.

(Apologies if anything above is self-evidently wrong to a real pilot - happy to be corrected if that's the case)

Jazz Hands

With reference to somatogravic illusion, without visual cues:

- Can a steadily increasing pitch-up, of the degree experienced by 447, be misinterpreted as acceleration?

- Can the deceleration of the aircraft (either by the initial speed reduction to M0.8, or the slowing resulting from the climb) be misinterpreted as pitch-down motion?

- If so, can the combination of the two - when taken with rapid vertical speed and altitude loss - be sensed as a steep dive instead of a pitched-up fall?

Sciolistes

I completely concur. The Airbus philosophy basically changed the game during a cricial phase of the recovery by altering the system and handling behaviour and produced inconsistent aircraft annunciations just when the crew were desperate for reliable information.

I sinerely hope for a proper objective professional comentary on this story. The Flight Global article and David Learmont blog contain spin, is not factual compared to the BEA report and mixes up the chronology implying the cause lies with the crew when clearly such an assumption is neither fair nor reasonable at this stage. The hand of Airbus Industries at work already?

sensor_validation

@auraflyer

My reading of the BEA document is that at least 2 out of 3 Pitot tubes were actually working correctly just before the real stall, but wouldn't have been trusted. We don't know what the 3rd pitot derived airspeed was displaying - it could have been reading high at this altitude if total pressure locked in from FL350.