AF447 Thread No. 3

[RR_NDB]

System "Pitot DSP are amplifying" Pitot problems?

Hi,

From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).

BEA sequence is: AP quits, AT quits, RH roll, PF action, SW, SW... Sharp fall from LH Pitot then a few moments later from ISIS Pitot

I suspect the "processing" of Pitot data (signal conditioning, voting, etc.) is amplifying Pitot problems. Probably (to be confirmed by FDR) AP, AT quit before ISIS showed lower speed.

The speed falling seems typical of stagnation point and not drain. And the event seems to be "short lived". Question? The a/c System needs this kind of sensitivity? Why can not during short duration failures remain alive? Well, this was discussed earlier and IIRC they are developing a "band aid" to deal with this "short term" Pitot failures.

In summary, my rationale is:

1) An EW seems to be simple to implement and may be could be useful (as a band aid) to alert to something more serious.
2) May be the a/c System can still operate properly using "improved" algorithms or even also using alternate data (while Pitotīs during short period are not delivering same output).
3) We need to power modulate Pitotīs with extra Watts (last but not least) while waiting R&D, Cert. and perhaps new type of sensors for "real redundancy".