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Comment by jabl | Hacker News Reader

Here's one example where loss of an elevator trim tab caused the pilot to experience +17G, leading to incapacitation/unconsciousness and a fatal crash: https://www.ntsb.gov/investigations/AccidentReports/Reports/...

(also a non-pilot, I found the above surprising, but there it is..)

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The plane in question was a highly-modified P-51 taking part in the Reno air races. Looking through the report it was routinely pulling 4G in the turns already (at ground speeds of 360-380kts) so quadrupling that in the face of structural failure isn't beyond belief.

It was pulling 4G turns by using the elevators. My surprise was that losing such a tiny piece as a single trim tab would cause a 17G pitchup.

But yes, that was a highly modified plane pushed way past any sensible operating limits, so maybe one shouldn't generalize too much from it.

This is where the NTSB report most directly addresses the issue: "...the loss of the left trim tab’s downward force on the elevator resulted in a concurrent sudden upward deflection of the elevator, a sudden and forceful aft movement of the control stick, the pitch-up of the airplane, and the rapid increase in G."

At this point, the trim tab was still attached, but its link assembly had broken.

In addition, the report notes "two major modifications to the elevators each made the airplane more sensitive in pitch control: the substantially increased elevator counterweights (about twice that of a stock P-51D) that overbalanced the elevators and the substantially decreased elevator inertia weight (less than half that of stock)."

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