Air France 447 - On topic only!

[Theoddkiwi]

I don't know what ACARS reports. Since it is maintenance oriented, perhaps a message would indicate high EGT or low thrust indications, or RPM instability. I really don't know.

I would suggest an ACARS message would be generated due to en Exceedance occurring of one form or another.

This would make sense as one of the big reasons for ACARS is to allow maintenance workers top prepare for an aircraft with a defect before it arrives. Exceedances cannot be cleared by pilots and must be recorded assessed and cleared by a LAME.

The beauty of ACARS is that Maintenance staff can be informed early rather than depend on the pilots to report problems before they land or at the gate. It also means issues are not errr over looked by the flight crews

I would be very surprised if 447 suffered some form of pre-crash engine problems. Given the initial info from the BEA and Airbus that no immediate issues have been found with the aircraft, this would support that.

[Evan]

From the reports anyway, there was a sudden and significant lifting, nose-up, and this in turn led to the stall. You seem to have it that the compressor stall occurred first, this leading to the pitching up and eventual wing stall (if I'm understanding).

No, I mean first of all I am only throwing out a list of possible factors. I think compressor stall or even flameout is a possible factor. I'm not convinced of anything beyond UAS at this point. But, sure, I suppose it could have gone that way.

[Fear_of_Flying]

No, I mean first of all I am only throwing out a list of possible factors. I think compressor stall or even flameout is a possible factor. I'm not convinced of anything beyond UAS at this point. But, sure, I suppose it could have gone that way.

Ok, well humor me a bit then. Suppose it happened that first the airspeed errors occurred, then the pilots commanded pitch up, and this in turn led to a deep stall (also reported) from which they were unable to recover. What are the possibilities that would have caused the pilots to increase the AoA to such a critical degree? I read that, not knowing their airspeed, it's possible they increased throttle, and this in turn could have pushed the nose up. Would this in itself have been sufficient? Could this simply have been an effort to avoid losing altitude? Another knee-jerk reaction?

Something else I read said that the autopilot could have commanded a surge in thrust (resulting in the pitch up), but if memory serves, that disengaged early on in the sequence of events. Plus one has to keep in mind the other report regarding pilot error.

[Gabriel]

... deep stall...

I thought I'd comment that a deep stall did not occur because this kind of planes are not susceptible to one. A deep stall happens when the the horizontal tail is "shadowed" into the wake of a stalled wing, thus loosing its ability to act as a stabilizer and its authority as pitch control. Of course, due to simple geometric reasons, this can only happen in T tails.

(FoF, I know that you are just quoting a newspaper article quoting a non-disclosed source reportedly close to the investigation)

[Evan]

Ok, well humor me a bit then. Suppose it happened that first the airspeed errors occurred, then the pilots commanded pitch up, and this in turn led to a deep stall (also reported) from which they were unable to recover. What are the possibilities that would have caused the pilots to increase the AoA to such a critical degree?

It's hard to imagine a qualified crew with a lot of flight hours between them stalling even under these circumstances. Perhaps the systemic issues I and Gabriel have previously identified, combined with the loss of stall protections, could have led to an inadvertent stall. IF they stalled the aircraft, it was probably the result of a sequence of misleading, confusing or distracting factors, and possibly the wrong survival instincts telling them to maintain altitude at all costs.

As for the pitching up moment associated with thrust, I think that is mostly a consideration at lower altitudes. When flying at FL35, there are two things to consider: Firstly, at that altitude and weight you are already using a high thrust setting for M.82, in the 85-90% N1 range I think. Even if they were slowing for turbulence they would probably have been using around 70% N1. Secondly, thrust has a very diminished effect due to the low density of the air, so thrust inputs need to be aggressive to have any real immediate effect. I don't think they could have done anything that would have resulted in a pitching moment that could lead to stall. The memory item calls for holding 5° pitch at full climb thrust (or maximum continuous power if one engine was surging). I can't imagine them going beyond that setting without airspeed data.

[Gabriel]

I read that, not knowing their airspeed, it's possible they increased throttle, and this in turn could have pushed the nose up.

Not if the flight control computers remained in abnormal alternate law (we know that they reverted from normal to abnormal alternate because there is an ACARS message, we don't know if it remained that way throughout the event).

Something else I read said that the autopilot could have commanded a surge in thrust (resulting in the pitch up), but if memory serves, that disengaged early on in the sequence of events.

Exactly. Unreliable airspeed comes with AP and AT disconnect, abnormal alternate law, rudder limmiter freezing at the last setting, and a dozen of instrument flags and EICAS messages.

[Fear_of_Flying]

I thought I'd comment that a deep stall did not occur because this kind of planes are not susceptible to one. A deep stall happens when the the horizontal tail is "shadowed" into the wake of a stalled wing, thus loosing its ability to act as a stabilizer and its authority as pitch control. Of course, due to simple geometric reasons, this can only happen in T tails.

(FoF, I know that you are just quoting a newspaper article quoting a non-disclosed source reportedly close to the investigation)

I apologize for so many amateur posts in one day, but it does feel that we're on the verge of learning what happened, and it's been a long time coming. With all this half-information now out there, I expect more will "slip out" soon, probably before the official release on Fri.

[Fear_of_Flying]

IF they stalled the aircraft, it was probably the result of a sequence of misleading, confusing or distracting factors, and possibly the wrong survival instincts telling them to maintain altitude at all costs.

As unlikely as it may seem, that's sort of what I'm thinking at this point.

[Evan]

Not if the flight control computers remained in abnormal alternate law (we know that they reverted from normal to abnormal alternate because there is an ACARS message, we don't know if it remained that way throughout the event).

Good point. The automated pitch trim on the A330 compensates for variations in thrust, and it was in effect throughout as far as we know.

[Gabriel]

It's hard to imagine a qualified crew with a lot of flight hours between them stalling even under these circumstances. Perhaps the systemic issues I and Gabriel have previously identified, combined with the loss of stall protections, could have led to an inadvertent stall. IF they stalled the aircraft, it was probably the result of a sequence of misleading, confusing or distracting factors, and possibly the wrong survival instincts telling them to maintain altitude at all costs.

And then, 35,000 ft is a lot of altitude to recover from a stall.

[Gabriel]

As unlikely as it may seem, that's sort of what I'm thinking at this point.

Whatever happened, it was something unlikely. In the current state of air travel safety every accident is an outlier.

[Fear_of_Flying]

I thought I'd comment that a deep stall did not occur because this kind of planes are not susceptible to one. A deep stall happens when the the horizontal tail is "shadowed" into the wake of a stalled wing, thus loosing its ability to act as a stabilizer and its authority as pitch control. Of course, due to simple geometric reasons, this can only happen in T tails.

(FoF, I know that you are just quoting a newspaper article quoting a non-disclosed source reportedly close to the investigation)

I did happen to find some differing opinions on deep stall on the pprune forum discussion which may explain the term's use in the media reports (http://www.pprune.org/tech-log/39510...esume-150.html)

A couple of comments:

Yes, [you need a T-tail a/c] for a classical deep stall. But if combined with a spin, you can produce a similar effect (a vortex) with non T-tail a/c. At which point, deep stall simply means a stall which you cannot terminate unless positive power input is available to re-attach air flow across control surfaces.

It depends how you define "deep stall". For some it just means an AoA substantially greater than that at which the stall first manifests itself. The T-tail problem is the airplane being "locked-in" in that condition.

[Harding]

I'd really feel safe flying with Evan & Gabriel at the controls.
/Spectator since june 2 -2009.

[Black Ram]

I'd really feel safe flying with Evan & Gabriel at the controls.

Highkeas and Theoddkiwi will take care of the maintenance. Myndee can take pictures.

[Peter_K]

I'd really feel safe flying with Evan & Gabriel at the controls.
/Spectator since june 2 -2009.

I would feel safe with Evans' Grandmother at the controls.