Having grown up around General Aviation, I've only seen one 421 accident that was due to mechanical failure. That occurred at Ft. Payne, Alabama some time ago when the aircraft carrying the city fathers experianced nose gear failure-linkage that locked the strut in the down position broke during the landing roll. No one hurt but the airplane was in the shop for some time thereafter. I saw it about a week after the accident and while it wasn't a writeoff, it was going to require extensive work. It was a nice airplane and I'd had a chance to take a ride in it around the circuit some time before the accident.
1millionflyer, my folks are indeed highly experianced pilots. Dad's certificate has Instrument, twin, aerobatic, glider and commercial ratings. Mom has Instrument, twin and seaplane ratings. They've always flown high performance aircraft, our first plane being a Cessna P210. We only had it for a few years, three or four at most. We decided that it lacked certain creature comforts that we desired given the frequent long flights that we made. They considered transitioning to a turboprop but decided on the Cessna 414 given that it had lower operating costs while outperforming many comparable King Airs and others. We've had the 414 longer than any other plane, going on fifteen years now.
Safety, as you mentioned is dependant on quality training, retraining and maintenance. Both Mom and Dad attend simulator training annually and do refresher and familiarization courses provided by the FAA and our maintenance company at TUS
. Most of the accident pilots are hobbiests for all practical purposes. They do not fly regularly and are often overconfident. All the technology can't save a fool from him/herself. A bad case of "getthereitis" can throw all safety technology to the wind. We've had times that we set down for hours just short of our destination to let the wx improve so that we could safely get in. As the old addage says, "Fools rush where angels fear to tread."
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."