PPRuNe Forums - View Single Post - Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash
Old 1st Apr 2019, 00:02
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ecto1
 
Join Date: Nov 2018
Location: madrid
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I've had a disturbing idea:

IF:

- Resolver coils inside the vane are at 45 degrees with the horizontal (Forming an X , not a +)
- Software block do not stop AOA calculation if a plausibility check is failed (sin^2 + cos^2 = Vmax^2) and does a funny average (AOA= (arcsin(sin) + arccos(cos))/2) instead of AOA=atan(sin/cos)

THEN:

(real nose AOA= resolver angle - 45 deg)

A short SIN to GND or COS to GND inside any computer (stall management for instance) or connector or wiring loom would cause the reading from the vane to have an offset of 22.5 degrees when the real AOA is mostly zero.

And if it's high resistance short, as it is often the case with FOD or chaffing, it may very well pass the installation test because the coil is sending a lot of amps to the short, but burn/short the coil or something after a while (say taxi to runway). That would also explain lack of dampening (something fusing/melting/overheating inside the vane) after the flight. That would also explain why at least two different computers sensed too high AOA, which clearly points to faulty sensors, without having to believe that two sensors failed in a row without any external help, which is an impossible coincidence. That will very well match with the conductive FOD inside computer hypothesis mentioned some posts ago (A/C Cb tripping, invalid AOA, fault SMYD computer...)

question: FDR traces show nose AOA or wing AOA (=nose AOA / 2 from what I read around here)?

I really hope it's not that simple.
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