Amateur-built YAK 52W N52KF accident near El Cajon, California

Probable cause

The pilot's failure to maintain directional control during taxi after a reduction in braking performance and steering capabilities due to his failure to reopen the air supply valve after the nonstandard engine start.

NTSB analysis

After completing an uneventful preflight inspection, the pilot was unable to start the engine due to low pressure in the pneumatic system. An individual arrived with a tank of air to pressurize the system while the pilot remained in the airplane. The pilot shut off the compressed air supply valve, as required during a pneumatic system recharge; however, the recharge could not be accomplished due to an incorrect adapter. While the individual left to find the correct adapter, another individual offered to help start the engine manually by turning the propeller. After the engine started, the pilot forgot to reopen the compressed air supply valve and, during taxi, the airplane experienced a loss of braking performance that affected its steering capabilities (the steering is accomplished through differential braking, and the brake system requires pneumatic pressure to operate). The pilot was unable to maintain directional control, and the airplane subsequently collided with a fence and sustained substantial damage to the left wing.

The checklist for the make/model airplane does not require the pilot to check the air pressure or valve position during the preflight, engine start, or before takeoff phases.

Text from the NTSB. Open the NTSB docket for WPR17LA214 for the full record.