Quick trim and a close shave

[Old Farang]

Quick trim and a close shaveQuick trim and a close shave | Flight Safety Australia (https://www.flightsafetyaustralia.com/2020/06/quick-trim-and-a-close-shave/)

About 90 seconds after take-off, at about 140 knots and a height of about 1400 feet AGL, a ‘pitch trim runaway’ spoken warning sounded and the pitch trim moved nose-down without any pilot or autopilot inputs. Despite pulling on the control yoke with both arms, the pilot was unable to stop a 2000-fpm descent from developing. Working from memory, the pilot enacted the emergency drill for pitch trim runaway. The ATSB found he inadvertently selected the flap interrupt switch rather than the trim interrupt switch. The two switches are close to each other on the central control pedestal.
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I encountered this in a helicopter once. It sure gets your attention! The problem with a helicopter is it may not be possible to let go of either control to pop a circuit breaker, even if you know which one it is! In my case the trim system on the cyclic used bias springs between the trim motors and the linkage, so with a bit of Popeye strength it was still possible to overcome the trim. Managed to get back on the ground for a change of underwear!

[Hugh Jars]

I had a full nose-up trim runaway (well, my student did), during his first session of circuits when I was doing his initial multi-engine endorsement. He was flying, so I didn’t realise until he had this strange look on his face and was pushing the controls hard forward.
By the time I reached over and hit the pitch trim master off, the motor had already stripped the drive at full nose-up.
So I took control with him assisting and we did some controllability checks. It really needed both of us to keep it stable in pitch.
So we made a mayday call and returned to Bankstown to a full turnout of the services[emoji23] We had a top air traffic controller on arrivals that day. He calmly cleared the way for us.
We managed a reasonable landing without further damage.
For our troubles I was abused by the owner’s engineer for writing up the defect! That’s the first and only time I’ve ever told an engineer to go f#%£ himself...

[Pedro_The_Swift]

Ok,, I'll ask.. [bighmmm]

whats a pitch trim runaway?

[JDNSW]

Pitch - aircraft nose up or down, controlled by pushing back and forward on controls

Pitch Trim - adjustment to the 'neutral' position so the nose can stay at the attitude wanted. Needs adjustment with changes in speed and power and whether climbing or descending (and other things as well). Commonly adjusted by an small switch on the control wheel (or purely manual on some basic aircraft). Usually an electric motor and gearbox adjusting some part of the tailplane (or the whole thing) or pulling on a spring.

Pitch Trim runaway - electrical or computer fault that operates the trim without input from the pilot. Can be disastrous - see 737MAX.

[superquag]

"...Pitch Trim runaway - electrical or computer fault that operates the trim without input from the pilot. Can be disastrous - see 737HAL...."

- But when the spoken warning says "I'm sorry Dave, I'm afraid I can't do that..." [bigsad][bigsad][bigsad]