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Old 14th Jun 2009, 07:39
  #1438 (permalink)  
The Chaser
Join Date: May 2009
Location: hot on the heels of worthy targets
Posts: 184
grizzled Well said.

JD-EE You ask the most important question above – "does the pilot have any better information?" = That is the question that remains unclear.

We know there is a procedure for the PF to fly pitch and N1, logically for this to happen successfully the PF needs Attitude and Engine data.

Prior to 02h14, there is no indication that engine data/function was irregular, that’s half of the picture, the other is still uncertain. ISIS did raise a fault, however systems experts have suggested that speed rather than attitude may have been affected. It has since been reported that the original ACARS transcript of ATA 3412 ISIS was in error. ACARS ATA 3422 ISIS is considered to be correct - which would indicate an L-gyro problem/indication), so it is possible that the PF did not have any Attitude reference, only N1 until 02h14. Obviously it remains to be seen whether (all things being equal and accurate) that procedure on that particular flight was a reasonable ask, both before and more importantly after 02h14.

What we also know (if the information provided thus far is accurate) is that the Automation decided that the information it was receiving was not (automated decision) sufficiently accurate to continue automated flight.

Hypothetical work through of what I read you to be asking - In the implied (ACARS) flight modes known before 02h14, were the A/P set up so that the PF was required to demand control from the A/P (otherwise the A/P would continue to fly) then the A/P will continue to react based on the data it ‘thinks’ is correct. What would be the A/P driven outcome if (as suggested) some of the speed indication scenarios discussed here were even party true? Would the automation react to chasing speeds, attitude, auto throttle etc in a reasonable and safe fashion? consider that the ‘protections’ would be (in that circumstance) operating on false information as well, in other words no protection at all.

An interesting technical discussion would be one exploring how well A/P and automatics would keep up if it had a ‘fallback’ [ISIS Attitude and N1 cruise] mode available in these sorts of rare circumstances, which is what I am reading your question to be alluding to.

Whether it is a pilot or the automatics, if either/both have no reliable attitude (primary or standby), nor accurate speed data etc, in IMC, the result is likely to be the same.

Good discussion.

Last edited by The Chaser; 14th Jun 2009 at 10:43. Reason: New ACARS transcription correction to ATA 3422 ISIS code
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