Not a pilot, but I’d love to see an incident report on that. What the heck would make a trim system do that? Sounds like a pretty serious bug…
Mike: I’m about as mystified as you. If you pull enough breakers the motor is supposed to stop, that’s for sure. I’m not an expert on the King Air, an American design from the 1960s that has been pushed aside by competition from the single-engine Pilatus PC-12 (Swiss-made). One possible explanation is that the autopilot and trim system had been modified/upgraded. Thus it is possible that the breakers were no longer labeled correctly and/or that the training program wasn’t 100% applicable to this particular aircraft.
Trim runaways are very rare but they have caused accidents. The newer the design of the airplane the more safeguards there are against something like this. On the PC-12 (first delivered 1994), for example, you need to press two switches to get the trim to move. There is a warning tone if the trim is moving and the buttons are pressed. There is an interrupt switch right by the power lever. And then there are breakers as a last resort.
I imagine wiring harnesses might develop shorts that can bypass the circuit breakers.
Not being an electrician, I can imagine that if the hot to a motor were to short with another hot, the motor would runaway and the circuit breaker would do nothing having in effect been diked out of the circuit.
I have a friend who had an uncommanded gear retraction eventually traced to such a short.
“an American design from the 1960s that has been pushed aside by competition from the single-engine Pilatus PC-12 ”
That’s an odd thing to say, considering that Beechcraft can’t make King Airs fast enough to meet the demand.
Jim: when Beech filed for Chapter 11 bankruptcy protection I took that to be a sign of poor financial health.
Is it not safe to fly without a teenage girl present in the cabin?
The real last resort is to physically grab and hold the trim wheel which is apparently what they did here. If this was not so rare an occurrence, it would make sense to have some kind of lock or clamp on the trim wheel that you could apply so you wouldn’t have to restrain it with your hand (but then you have the problem of the lock getting applied accidentally).
I suppose it is possible to develop a short so that the trim wheel motor is getting power from another circuit or maybe the aircraft was somehow modified improperly so that the breakers on the checklist weren’t really the right ones, but if I had to guess, I would guess that in the panicky moments when this happened, the pilot threw the wrong breakers and that’s why it didn’t go off. Pilot error accounts for something like 90% of general aviation accidents.
Not a pilot, but I’d love to see an incident report on that. What the heck would make a trim system do that? Sounds like a pretty serious bug…
Mike: I’m about as mystified as you. If you pull enough breakers the motor is supposed to stop, that’s for sure. I’m not an expert on the King Air, an American design from the 1960s that has been pushed aside by competition from the single-engine Pilatus PC-12 (Swiss-made). One possible explanation is that the autopilot and trim system had been modified/upgraded. Thus it is possible that the breakers were no longer labeled correctly and/or that the training program wasn’t 100% applicable to this particular aircraft.
Trim runaways are very rare but they have caused accidents. The newer the design of the airplane the more safeguards there are against something like this. On the PC-12 (first delivered 1994), for example, you need to press two switches to get the trim to move. There is a warning tone if the trim is moving and the buttons are pressed. There is an interrupt switch right by the power lever. And then there are breakers as a last resort.
I imagine wiring harnesses might develop shorts that can bypass the circuit breakers.
Not being an electrician, I can imagine that if the hot to a motor were to short with another hot, the motor would runaway and the circuit breaker would do nothing having in effect been diked out of the circuit.
I have a friend who had an uncommanded gear retraction eventually traced to such a short.
“an American design from the 1960s that has been pushed aside by competition from the single-engine Pilatus PC-12 ”
That’s an odd thing to say, considering that Beechcraft can’t make King Airs fast enough to meet the demand.
Jim: when Beech filed for Chapter 11 bankruptcy protection I took that to be a sign of poor financial health.
Is it not safe to fly without a teenage girl present in the cabin?
The real last resort is to physically grab and hold the trim wheel which is apparently what they did here. If this was not so rare an occurrence, it would make sense to have some kind of lock or clamp on the trim wheel that you could apply so you wouldn’t have to restrain it with your hand (but then you have the problem of the lock getting applied accidentally).
I suppose it is possible to develop a short so that the trim wheel motor is getting power from another circuit or maybe the aircraft was somehow modified improperly so that the breakers on the checklist weren’t really the right ones, but if I had to guess, I would guess that in the panicky moments when this happened, the pilot threw the wrong breakers and that’s why it didn’t go off. Pilot error accounts for something like 90% of general aviation accidents.