Originally Posted by
ecto1
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It has a very specific behaviour: 10 or 12 degrees offset, higher on the left at power - up, fairly stable on both sides, then during taxi hardly any real movement at any side, but several (6 or 8) short instances of left AOA vane reading ramping up a few degrees at a time, not vertically (cliff) but at a slope, increasing the offset to about 25 deg, then at rotation the right one increases (normal) the left one decreases (abnormal) and then both set at 22 degrees offset and seem to measure quite faithfully to each other (apart from the offset) for the rest of the flight.
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To me the only two explanations that so far match (loosely) are:
- a slipping shaft that slips with the bumps but sticks with aero forces (but two sensors in a row, I don't think so)
- a intermittent electrical connection outside of the probe somewhere in a encoder-like signal which is disturbed by the bumps of taxi and creates an offset. Perhaps at the control module or power to the probe.
I don't think any of them is very probable, though. There must be a better explanation. Although bit corruption or software bug doesn't fit any better to me.
One report that I have for JT says that, in Jakarta :
The technician cleansed the Air Data Module (ADM) pitot and the left static port to repair the IAS and ALT disagree along with operational tests on land with no results. Then the Technician cleaning the electrical connection at the Elevator Feel Computer is accompanied by an operational test with good results.
Who here knows what those "operational tests" might have involved?
Are there any such, approved operational tests?
What approved operational tests might have been carried out that could have shown "no fault" when a fault still existed?