We had a Huey B model that did something questionable and the fleet was grounded. Engineers combed the aircraft, no obvious fault found, did a D service, and I took it up for the Post-D test flight schedule, it was the smoothest in the fleet. But I didn't want to release it yet.
A USN TPS-qualified test pilot who was transiting the base was called in, and the next day he took it out with the original crew who had the incident, and for a completely different reason, the tail rotor and gearbox came off, mast strike, blade separation and ballistic from 1500'.
I felt horror, and I felt lucky.