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by cjbprime
2638 days ago
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It doesn't present as runaway trim, though. It's a small change in the trim, repeated every few seconds, which can be counteracted on the control column but will eventually add up. Small trim changes are usually happening all the time. |
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In a typical run-away trim, the trim wheel will move a great distance. It's very noticeable, both audibly (the wheel makes a clack-clack-clack noise) and visibly (there are white paint flashes on the wheel). And, obviously, the plane nose goes up or down by more than expected. The correct remedy is to disable the auto trim control via switches on the panel (located near the trim wheels).
The MCAS will adjust the trim in small increments every 10 (or is it 20?) seconds. Yes, a pilot should notice this, but because it's intermittent, it's more likely they don't "see" it as run-away trim, and just a slightly abnormal trim (EDIT - problem made worse because pilots were not informed MCAS existed - it's not a failure more they have trained on). They may attempt to remedy this with the manual trim control (a rocker switch on the control yoke). This does NOT disable MCAS, it only re-trim the plane. MCAS will re-engage due to faulty AoA sensors repeatedly until either the pilot disables all auto-trim with the switch on the panel OR the plane runs into the ground.