Amateur-built CX4 N274DR accident near Upland, California

Probable cause

The inflight separation of the propeller assembly due to a fatigue fracture of the crankshaft. Contributing to the accident was the pilot’s restricted visibility during landing, which resulted in an excessive approach speed, a long landing, and subsequent impact with terrain.

NTSB analysis

The pilot reported that while returning to the airport after an uneventful flight, the propeller separated from the engine, which resulted in the windscreen and canopy being covered with oil and restricting forward visibility. The pilot continued toward the airport; however, as the airplane crossed the threshold of the runway, he noted that he was going way too fast as he was attempting to keep the airplane aligned with the runway. Subsequently, the airplane touched down near the departure end of the runway, bounced, and impacted the ground.

Postaccident examination of the airplane revealed substantial damage to the fuselage and both wings. The propeller assembly and a portion of the engine crankshaft was separated and not located.

Examination of the remaining portion of the crankshaft revealed that two fractures initiated at the termination of a square keyway slot in the crankshaft. The presence of ratchet marks at the fracture origins and the presence of progressions marks along the fracture path were indicative of fatigue fracture initiation and growth.

Text from the NTSB. Open the NTSB docket for WPR20LA193 for the full record.