Accident Overview
On June 24, 2020, at about 1145 Pacific daylight time, a Thatcher CX4, registration N274DR, was substantially damaged during an accident at Cable Airport (CCB), Upland, California. The pilot was seriously injured. The flight was conducted as a Title 14 Code of Federal Regulations Part 91 personal flight.
Sequence of Events
The pilot reported that he was returning to CCB after an uneventful local flight when the propeller separated from the engine. At that time, the airplane was about 1 mile from the airport at an altitude of about 1,100 ft above ground level. Oil covered the windscreen and canopy, restricting forward visibility. Despite this, the pilot continued flying toward the airport. As the airplane crossed the runway threshold, it was about 50 ft above ground level and traveling at a high speed. The pilot attempted to align the airplane with the runway by looking out to the side. The airplane touched down near the end of the runway and bounced. It continued over a fence and collided with a dirt berm.
Aircraft Damage and Examination
Postaccident examination by the pilot revealed substantial damage to both wings and the fuselage. The propeller assembly and a portion of the engine crankshaft had separated and were not located. The remaining portion of the crankshaft from the Hummel VW 2400CC engine was sent to the National Transportation Safety Board Materials Laboratory for examination.
Crankshaft Examination
Examination of the crankshaft revealed two fractures that initiated at the termination of a square keyway slot. The presence of ratchet marks at the fracture origins and progression marks along the fracture path were indicative of fatigue fracture initiation and growth.