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> It's possible that aerodynamic load (of the stabilizer opposing the elevator) made it physically impossible to manually trim given any mistrim at the time the
by kayfox 8y ago
> It's possible that aerodynamic load (of the stabilizer opposing the elevator) made it physically impossible to manually trim given any mistrim at the time the cutout happened, given the airspeed they had.
Its been noted in previous discussions that while it would be difficult, the load can be overcome if both pilots were to operate the manual trim wheel at the same time.
Not that its a good situation to be in.
- 3JPLW 8y agoIs it still possible at or near VMO? And when the trim is maxed out? I don't think I've seen an authoritative answer on that, and that's the situation they faced.
- cjbprime 8y agoAnother commenter pointed out that the captain is pulling back as hard as he possibly can on the yoke; releasing it to turn a trim wheel instead may have been just as deadly.
- VBprogrammer 8y agoIf my reading of the graphs is correct they are above Vmo for most of the episode. I'm surprised the flight surfaces weren't torn from their hinges.
- na85 8y agoVmo incorporates a factor of safety in its specification, so exceeding it is not a "parts fall off the aircraft" event. Vne is where things start to get scary because it's usually based on flutter, which can catastrophically damage/destroy the aircraft in very short order.
- VBprogrammer 8y agoYes. But it doesn't include full control deflections and certainly not control deflections in opposition to one another. Even at Va rapid control movements and control movements in multiple axes can permently damage the aircraft.
- na85 8y agoCorrect
- cjbprime 8y ago> Its been noted in previous discussions that while it would be difficult, the load can be overcome if both pilots were to operate the manual trim wheel at the same time. I haven't seen that noted anywhere, and have seen it theorized as impossible without motor assist, given their airspeed and with the elevator opposing. Got a link?
- deleted 8y ago[deleted]
- swhitt 8y agoManual Stabilizer Trim Excessive airloads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually. https://www.pilot18.com/wp-content/uploads/2017/01/B737NG_FCTM_31-10-05.pdf https://www.pilot18.com/wp-content/uploads/2017/01/B737NG_FC... page 312 (8.16)
- cjbprime 8y agoTo be clear, that's a link that agrees with me that it can be impossible, not a link that says they just needed to work harder. It's also from a 20 year-old manual, and isn't present on newer manuals, and pilots haven't trained on it in decades. Not appropriate to expect pilots to know, and possibly not helpful here: the pilots were low altitude, so allowing the nose to drop even further (to relieve aerodynamic load) may have been deadly too.
- swhitt 8y agohttps://www.satcom.guru/2019/04/stabilizer-trim-loads-and-range.html https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra... does a pretty good job of summarizing it I think. It sounds incredibly difficult to do.