Narrative:

I am a check airman and just gave a simulator [training session]. We finished early and the crew asked to go through some trim scenarios. This may be common knowledge; but if not; I wanted to put it on paper. 1) the qrc/QRH guidance for 'trim runaway' has 'grasp and hold' as the final step. This does not work with fast trim. It works with slow autopilot trim; but if the wheel is spinning under fast trim; there is no human way to grasp it and stop it. I burned my hand; nobody else was able to stop it running away. When 'trim runaway' was presumed to be an autopilot-only situation; this made sense; now that we know the aircraft can command fast trim; this needs to be addressed. This manual needs to be updated. 2) when the trim is set very far forward; and the pilot flying is hauling back on the yoke to keep from descending; the manual trim wheel (stab trim cutout switches to off) resists turning. This may have to do with pressure on the jackscrew; the trim is forcing down; the elevator forcing up; but once the trim is really far out of sync with flight conditions; it is nearly impossible to manually move the trim wheel to regain proper trim. The force is exceptionally difficult; it feels like there is a brake on the trim (probably the jackscrew). The pilot flying 'gave up' less than a minute into manually trimming. High airspeed (I pushed the throttles forward on him) made it much worse. He had to pull the throttles back to even get a turn in.this might all be coming out in testing; but from a ten-minute exercise; it became clear that there are more complicating factors to examine than just training on hitting the stab trim cutout switches. If the trim is too far out before that happens; what we've been taught doesn't seem to work very well; or at all. 'Grasp and hold' being the directive that simply is unfeasible except under autopilot trim runaway and then manually trimming to regain neutral control inputs is also nearly impossible. I wanted to put my experience down for you to look at. I've rarely been surprised by aircraft response; [so] watching the trim wheel bind up was an eye-opener. Simulator trim experiment shows inadequacy of guidance.

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Original NASA ASRS Text

Title: Air Carrier Captain reported the runaway stabilizer procedure was inadequate when demonstrated in the aircraft simulator.

Narrative: I am a Check Airman and just gave a simulator [training session]. We finished early and the crew asked to go through some trim scenarios. This may be common knowledge; but if not; I wanted to put it on paper. 1) The QRC/QRH guidance for 'trim runaway' has 'grasp and hold' as the final step. This does not work with fast trim. It works with slow autopilot trim; but if the wheel is spinning under fast trim; there is no human way to grasp it and stop it. I burned my hand; nobody else was able to stop it running away. When 'trim runaway' was presumed to be an autopilot-only situation; this made sense; now that we know the aircraft can command fast trim; this needs to be addressed. This manual needs to be updated. 2) When the trim is set very far forward; and the Pilot Flying is hauling back on the yoke to keep from descending; the manual trim wheel (stab trim cutout switches to off) resists turning. This may have to do with pressure on the jackscrew; the trim is forcing down; the elevator forcing up; but once the trim is really far out of sync with flight conditions; it is nearly impossible to manually move the trim wheel to regain proper trim. The force is exceptionally difficult; it feels like there is a brake on the trim (probably the jackscrew). The Pilot Flying 'gave up' less than a minute into manually trimming. High airspeed (I pushed the throttles forward on him) made it much worse. He had to pull the throttles back to even get a turn in.This might all be coming out in testing; but from a ten-minute exercise; it became clear that there are more complicating factors to examine than just training on hitting the stab trim cutout switches. If the trim is too far out before that happens; what we've been taught doesn't seem to work very well; or at all. 'Grasp and hold' being the directive that simply is unfeasible except under autopilot trim runaway and then manually trimming to regain neutral control inputs is also nearly impossible. I wanted to put my experience down for you to look at. I've rarely been surprised by aircraft response; [so] watching the trim wheel bind up was an eye-opener. Simulator trim experiment shows inadequacy of guidance.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.