Coming out of Quarantine
Presumably, this afternoon, you guys have been discussing the BEA "Update on Investigation". For what it's worth, I've been in voluntary quarantine since just before it came out. As soon as it appeared on the BEA website, I cut myself off completely from PPRuNe, all other media, and any contact with aviation-minded people; and that situation still pertains as I write. I deliberately progressed very slowly through the paper, taking notes and some very long stretch-breaks. There were a number of surprises. Since then, I've been mulling it over, and drafting this.
So what you are about (not/partially) to read are questions and comments arising from my own interpretation of the BEA account, uncoloured since its publication by the wisdom of third parties such as your good selves, and burdened by my limitations. No doubt, I'll have missed many points that, to you, are already "old hat". Nevertheless, here are my thoughts.
QUESTIONS & COMMENTS ARISING
(1) Why no R/H ASI parameter in DFDR? Would it be in QAR? The two recorded ASIs use pitots on the L/H side. (The PF was in R/H seat, presumably.)
(2) "From" 02:10:05, at what stage did the L/H (PNF's) ASI and ISIS ASI readings fall sharply from 275 to 60? After the two stall warnings, or before?
(3) Why did PF allow/encourage/command A/C to climb 3000ft and up to +16 pitch after receipt of stall warnings? One of the pilots had selected TOGA thrust, presumably in response to them.
(4) Why did/does the FBW system in Pitch-Alternate Law continue nose-up trimming of the THS past the stall-warning level of AoA?
(5) As the THS remained at 13 deg UP throughout the descent, is there any possibility that the THS motor stalled during down-elevator inputs? (The BEA "finding" is that "the inputs by the PF were mainly nose-up"[my emphasis of "mainly"].
(6) At about 02:11:04 (at the apogee of FL380), the L/H ASI and ISIS ASI showed 185kts. Was the R/H ASI showing a higher value – possibly due to a blocked drain-hole PLUS the climb of 3000ft?
(7) Quote from BEA: "At around 2 h 11 min 40 [6], the Captain re-entered the cockpit. During the following seconds, all of the recorded speeds became invalid and the stall warning stopped.
Note: When the measured speeds are below 60 kt, the measured angle of attack values are considered invalid and are not taken into account by the systems. When they are below 30 kt, the speed values themselves are considered invalid."
[FONT=Verdana][SIZE=2]Why are the AoA values considered invalid below 60kts IAS when the A/C is not on the ground?
(Looks at this stage that: first the PF has mis-controlled the A/C into an inappropriate, steep climb, despite a stall warning; but now the systems are failing to inform him that he has stalled the A/C.)
(8) In the descent, why did neither pilot seem to recognise that the A/C was even in a stall, let alone a deep/super stall? Why was idle thrust selected?
(9) At 02:12:02, several thousand feet below FL350, does the PF's comment that he had no more indications indicate that his ASI reading had only just dropped to a value that he no longer believed? Is it remotely possible that, perhaps unlike the others, the drain hole of his pitot tube had blocked at the same time as the intake? During the initial climb, could he have thought that his ASI was still valid, and that he was trying to avoid an overspeed? [See (6) & (7), above.]
SUMMARY OF KNOWN ENERGY ASPECTS (from BEA text and diagram)
02:08:07 – 02:10:05 (~15nm)
FL350 (about 37000ft amsl). Average GS ~450kts.
[FONT=Verdana]02:10:05 – 02:10:51 (~5.4nm)
FL350, then climbing steeply. Average GS ~420kts.
02:10:51 – 02:11:40 (~4.3nm)
Climbing to apogee of FL380 (about 40000ft amsl), then descending steeply through FL350, all with TOGA thrust. Average GS ~320kts.
02:11:40 – 02:14:28 (Tear-drop track-distance unknown)
Descent from (passing) FL350 (about 37000ft amsl) to sea-level, Thrust reduced from TOGA to ~IDLE by 02:12:02.
Footnote
During the couple of hours I spent reading this short report (including going back and forth), making notes, and referring to system diagrams, I made several unnecessary errors with my printer. Some sheets had to be discarded and fresh attempts made. The flight crew had less than three minutes to diagnose the problem, take action, and recover from any mistakes.