Usually solid state stuff should be pretty dependable, but silicon
devices don't like reversed polarity spikes. These can happen if the
master contactor ever stutters when the starter is engaged. I'm
surprised there isn't more transient protection in avionics and solid
state regulators.

I realize that this particular failure sounded like a vibration
problem, but a few more isolating and shunting diodes in our
electronics would seem to help reliability a lot.