(P)ilot (I)nduced (T)rim (R)unaway - for those that don't create acronyms in their sleep, like I seem to do....
I had an interesting experience - totally my own fault) on my recent trip up to Oshkosh - thought that sharing it might help others to recognize/understand what can happen. I was cruising along, VFR above a haze layer, autopilot on, no bumps - everything normal, just waiting for the mileage to the fuel stop to click down. I had pulled out my bound chart book and was looking at some interesting feature to pass the time when I suddenly felt a significant pitch up, looked up, and saw clouds - the airplane appeared to be trying to loop!
My first reaction was forward pressure on the stick, and that quite quickly and successfully arrested the motion, so nothing bad happened - I probably gained 300 feet total. I started trimming nose down, and glanced at the indicator - sure enough, it was significantly nose up. My first thought was a malfunction, but that lasted only a second before I recognized what had happened. I had obviously hit the coolie hat with my map book. I do not have a trim sensing altitude hold unit, so it held altitude as long as it could, and then suddenly disconnected when the forces became to much for it. That accounted for the "sudden" nature of the pitch up. According tot he G-meter, I never got more than 2 G's (and that might have been leftover from a turn on climb out), so it really wasn't much of an event - but could certainly surprise someone if they'd never heard of it.
I'm not going to over-react and include a trim disable switch for when I'm reading maps....just going to be more careful now that I had it happen. I guess the most significant "new" information was how the autopilot let it get significantly out of trim before releasing. Watch for it, don't panic - and don't' bump your trim hat with your maps!
Ya' learn something new every day....or you're not trying hard enough!
Paul
I had an interesting experience - totally my own fault) on my recent trip up to Oshkosh - thought that sharing it might help others to recognize/understand what can happen. I was cruising along, VFR above a haze layer, autopilot on, no bumps - everything normal, just waiting for the mileage to the fuel stop to click down. I had pulled out my bound chart book and was looking at some interesting feature to pass the time when I suddenly felt a significant pitch up, looked up, and saw clouds - the airplane appeared to be trying to loop!
My first reaction was forward pressure on the stick, and that quite quickly and successfully arrested the motion, so nothing bad happened - I probably gained 300 feet total. I started trimming nose down, and glanced at the indicator - sure enough, it was significantly nose up. My first thought was a malfunction, but that lasted only a second before I recognized what had happened. I had obviously hit the coolie hat with my map book. I do not have a trim sensing altitude hold unit, so it held altitude as long as it could, and then suddenly disconnected when the forces became to much for it. That accounted for the "sudden" nature of the pitch up. According tot he G-meter, I never got more than 2 G's (and that might have been leftover from a turn on climb out), so it really wasn't much of an event - but could certainly surprise someone if they'd never heard of it.
I'm not going to over-react and include a trim disable switch for when I'm reading maps....just going to be more careful now that I had it happen. I guess the most significant "new" information was how the autopilot let it get significantly out of trim before releasing. Watch for it, don't panic - and don't' bump your trim hat with your maps!
Ya' learn something new every day....or you're not trying hard enough!
Paul