[lemetier]

Originally Posted by eluded

Maybe bad tubes that indicated incorrect air speed? Plane was probably not under manual control at the time. This causes bad things to happen when automation relies on correct air speed. If you're not trained properly you won't notice until bad things start to happen and then it will be too late.

This wasn't a "Pitot Tube" issue and the plane was being hand flown. I suspected an AoA problem early on and this was released overnight:


The Boeing Company

Flight Crew Operations Manual Bulletin

Number: TBC-19

Issue Date: November 6, 2018

Airplane Effectivity: 737-8 / -9

Subject: Uncommanded Nose Down Stabilizer Trim Due to Erroneous Angle of Attack (AOA) During Manual Flight Only

Reason: To Emphasize the Procedures Provided in the Runaway Stabilizer Non-Normal Checklist (NNC).

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.
- [COLOR="DarkRed"]IAS DISAGREE alert[/COLOR].
- [COLOR="DarkRed"]ALT DISAGREE alert[/COLOR].
- AOA DISAGREE alert (if the AOA indicator option is installed)
- [COLOR="DarkRed"]FEEL DIFF PRESS light[/COLOR].

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 [COLOR="DarkRed"]and stay in the CUTOUT position for the remainder of the flight.[/COLOR]