There have been several aircraft that have had major accidents due to equipment problems. These problems have been electrical components that have gone “outside their regular job functions” and over controlled the aircraft causing a serious accident or accidents. One of the recent problems has involved out of control trim problems.
When I was at Braniff years ago, and I mean “years ago,” we had an emergency runaway stabilator problem on the Boeing 727 that required three (3) measures to stop the problem. One was switch off the “stabilator trim switch.” The second was pull the circuit breaker. And finally, the last resort was the Flight Engineer had to rotate his seat around and put his foot on the large stabilator trim wheel. This was to stop an extreme out of control pitch change problem in a very large aircraft, that being the Boeing 727.
What do we do on large pressurized aircraft? The procedure is to chase down the circuit breaker if the trim disconnect (some autopilots have them some don’t) does not stop the trim problem. Trim problems can be very serious. A recent Twin Cessna 340 with a retired American Airlines pilot lost an aircraft on an autopilot flight check. The plane went totally out of control. What was the solution?
The key was GET RID OF THE ELECTRICAL INPUT. We have consistently taught on the large aircraft piston or turbine, TURN OFF THE BATTERY AND THE ALTERNATORS. YOU HAVE TO DO BOTH AND THERE IS A “GANG BAR” FOR THESE IN THE TWIN CESSNA AIRCRAFT. You do not have to chase the circuit breaker if you just turn off the main electrical source. If it is an electrical problem, turn off the battery and alternators. If you just kill the batteries the alternators will continue to power the main bus. Don’t chase the circuit breaker! Pull the main power source.
Train Hard. Fly Safe.