Computers
Gentlemen,
computers will always do what their programming tells them to do. Sure.
First caveat is "programming" takes human beings, who make mistakes, be they engineers in a design committee, or pilots on a flight deck.
Second caveat is when physical failures affect the computerized system.
Is it not obvious in our present case that a "physical" fault occured : wiring ?
BEA offhandedly ascribing it to "PRIM2 rejected ADR1" is a feeble excuse for an explanation. No mention of "wiring" ?
I have reliable confirmation from the relevant documents that this failure :
WRG:ADIRU1 BUS ADR1-2 TO FCPC2
is indeed a "wiring" fault, between ADR1 and PRIM2.
This fault appears "simultaneously" (look at ACARS and CMC time stamps) with the acknowledgement by the system that speeds have gone haywire :
PROBE PITOT 1X2,2X3,3X1
These faults are unrelated : wiring + icing. How can this be ?
Has this strangest of dual failures ever been foreseen ?
How can one expect the design to operate as advertised in this likely un-designed for situation ?
Does anyone have reliable information as to the exact state of PRIM2 operation after this combination of faults ?
How can anyone be certain that PRIM2 did indeed latch Alternate 2 Law ?
How can one be sure it did compute identical to PRIM1 & PRIM3 when it is obvious its state is different ?
What happens if PRIMs differ in their assessment of the outlier ADR ?
What happens if, after their 10 seconds ADR cross-checking "window", PRIMs end up in different states, deciding on different flight laws ?
Has anyone considered what could happen to PRIM2 if it lost datalink with ADR1 at the very moment when the PRIMs tried to eliminate the outlier ADR ?
Has anyone studied carefully the first BEA interim report and extracted the PRIMs behaviour at the start of UAS sequence ?
I did. PRIM2 could very well have reverted to Normal Law. With erroneous data fed into it. Definitely not designed for. But quite possible.
Please, do prove me wrong. Do not recite the manufacturer's mantra, I know it and I do not care what the salesmen say. Sh't happens but it does not sell.
So many people posting here assume that the computers reacted "as expected", confusing it with "as programmed". I am deeply disturbed at seeing so many people who work in science and technology embrace blind religious faith into man-made technology. Where has the scientist's healthy doubt and critical judgement gone ?
Any high-tech item is an artifact : man-made. It is never perfect. It fails, even if rarely. It errs. It does unexpected things.
I am of the opinion that in this instance, statistically remote, it did unexpectedly err, compounding a surprising but otherwise manageable situation into something far more dangerous and incredibly difficult to understand in a limited amount of time.
The initial pitch-up, more than 10 degrees nose-up attitude, up to +7000fpm vertical speed, +3000ft altitude deviation, has been discussed quite a lot. Such discussion is always along the lines of :
- deliberate pilot action : then why ?
- unintended pilot action : then how ?
Outraged whys and hows all over. Naive reaction to a very narrow extract of all the available data, delivered to the press at a commercially critical time. Understandable coincidence.
So few are those who suggested it could have been undesired, an unexpected reaction from the aircraft itself, its flight controls computers confused.
Why is this possibility unacceptable for so many involved people ? All aircraft types, from all manufacturers, have at times suffered serious design-induced malfunctions which caused crashes. Such problems are rare. All modern jet airliners are statistically safe. Why the reluctance to acknowledge a very specific flight controls problem ? Why the brand of blasphemy when such problem is invoked ? Why the need to invoke "pilot error" when questions point towards the manufacturer and its design ? This blame-shifting attitude is contrary to the necessary openness and honesty that could improve flight safety. I find it very much akin to religious intolerance.
If pilot error is to be found in this case, it is twofold :
- calling for the Captain to come back to the flight deck used up resources which should have been entirely allocated to flying and cross-checking instruments, control inputs and results between PF and PM, especially in the early stages of the accident sequence. This could have allowed identification and isolation of a flight controls issue.
- failure to quickly and decisively use manual pitch trim, against training, in a flight law that usually excludes its use, to effect the desired attitude and trajectory if sidestick was found insufficient. This could have maintained a safe path against the undesired actions of confused computerized flight controls enough for extended troubleshooting.
These are real things that can really be corrected both in the attitude and flying skills of modern age airline pilots. These can improve flight safety. But the initial 3000 feet climb, 10 degrees and more pitch-up is unlikely to be "pilot error", even though some powers that be, and hordes of blindly faithful technology worshippers would prefer it to be so.