Beech H35 N4689D accident near Parker, Arizona

Probable cause

The improperly attached fuel line and cracked fuel diaphragm due to unknown personnel’s inadequate maintenance, which resulted in the loss of engine power during cruise flight and the subsequent forced landing onto rough terrain.

NTSB analysis

The flight instructor and pilot-rated owner were operating the airplane in cruise flight when the engine lost power. They manipulated the engine and fuel controls in an attempt to regain engine power, but the engine would not restart. They subsequently conducted a forced landing onto rough terrain. During the landing roll, the nose landing gear folded underneath the airplane, and the right wing sustained substantial damage.

The engine was test run, and it would not maintain power unless the electric boost pump was operating. During a postrun examination of the engine, the fuel return line from the engine-driven fuel pump was found loose at the pump connection, and fuel was noted dripping from the rigid fuel line near the pump connection. The line was removed, and the "B" nut ferrule was found cracked. The "B" nut and the fuel pump fitting threads were damaged. The fuel pump and fuel control assembly were found intact, and, during a test run, functioned properly. During testing of the fuel manifold valve, a leak was observed at the vent port, indicating that the diaphragm was compromised. Based on this evidence, it is likely that the improperly attached fuel return line on the fuel pump and the leak from the fuel manifold valve led to a loss of pressure in the engine fuel delivery system, which resulted in the loss of engine power. The investigation could not determine when or by whom the maintenance was performed.

Text from the NTSB. Open the NTSB docket for WPR14LA199 for the full record.