Maintenance personnel’s failure to perform required fuel system tests to ensure that the airplane met its original type certification basis after modifying the fuel system and the Federal Aviation Administration’s improper approval of the fuel tank modification via the field approval process during which it did not ensure that the required fuel system tests were performed, which led to the pilot’s inability to determine the airplane’s actual amount of usable and unusable fuel and the subsequent loss of engine power due to fuel starvation.

The pilot's selection of unsuitable terrain for landing, which resulted in a runway excursion, collision with terrain, and nose over.