On the 4th of April 1976 I had a runaway trim on a Aztec VH-MBU. If I remember correctly the trim cable was a nine strand affair and seven strands severed and poked through the cabin ceiling lining. The nose went down and the only way I could regain control was to lower the flaps (way outside the flap limit). With reduced power and flaps I was able to make a safe landing. The Aztec had a large nose up pitch tendency with the application of any flap up to the 'E' model. Piper then redesigned the tail plane on the 'F' model to eliminate this. If I had been in an "F' I probably wouldn't be here.
Part of the redesign of the tail plane included small horns on the leading edge and these would love to collect ice causing the control column to pump in and out. Interesting to see the accident aircraft here is an 'E'.
The janitrol heater required careful operation and would pop the circuit breaker if outside its temperamental parameters. I never liked that design.