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Old 7th Nov 2018, 14:19
  #733 (permalink)  
DingerX
 
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That "journalistic" website that doesn't like to cite sources claims to have posted the bulletin in question:
The Indonesian National Transportation Safety Committee has indicated that Lion Air flight 610 experienced erroneous AOA data. Boeing would like to call attention to an AOA failure condition that can occur during manual flight only.

This bulletin directs flight crews to existing procedures to address this condition. In the event of erroneous AOA data, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds. The nose down stabilizer trim movement can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 seconds after the electric stabilizer trim switches are released. Repetitive cycles of uncommanded nose down stabilizer continue to occur unless the stabilizer trim system is deactivated through use of both STAB TRIM CUTOUT switches in accordance with the existing procedures in the Runaway Stabilizer NNC. It is possible for the stabilizer to reach the nose down limit unless the system inputs are counteracted completely by pilot trim inputs and both STAB TRIM CUTOUT switches are moved to CUTOUT.

Additionally, pilots are reminded that an erroneous AOA can cause some or all of the following indications and effects:

- Continuous or intermittent stick shaker on the affected side only.
- Minimum speed bar (red and black) on the affected side only.
- Increasing nose down control forces.
- Inability to engage autopilot.
- Automatic disengagement of autopilot.
- IAS DISAGREE alert.
- ALT DISAGREE alert.
- AOA DISAGREE alert (if the AOA indicator option is installed)
- FEEL DIFF PRESS light.

In the event an uncommanded nose down stabilizer trim is experienced on the 737-8 /-9, in conjunction with one or more of the above indications or effects, do the Runaway Stabilizer NNC ensuring that the STAB TRIM CUTOUT switches are set to CUTOUT and stay in the CUTOUT position for the remainder of the flight.
In short, bad AOA data is sufficient to cause the reports of UAS and STS acting backwards. The maintenance writeups implicitly made a diagnosis, and it looks like nobody down the line went back to the causes and inferred the problem. For that matter, go back and read the discussion here and see what was said about the AOA sensors. It's still a head-scratcher.
And, to reply to a comment from pages above, no this is not a case where "just hand-fly" would be the worst thing to do. The sensor failure kicked off the automatics, and there was no choice. The guidance in the bulletin is a "reminder" of the procedure to follow if the aircraft is trying to trim the nose into the ground.
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