Incident
On September 23, 2017, about 1415 Pacific daylight time, an experimental SC Aerostar SA, Yak-52W airplane, registration N52KF, sustained substantial damage while taxiing at Gillespie Field Airport (SEE) in El Cajon, California. The airline transport pilot and the passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight under visual meteorological conditions. No flight plan had been filed.
Sequence of Events
The pilot conducted a normal preflight inspection and completed the starting engine checklist. He attempted to start the engine but was unable 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. The individual realized they had brought the wrong adapter and left to find the correct one. A second individual arrived and offered to manually turn the propeller to start the engine. The pilot accepted, and the engine was started.
The pilot completed the post-start checklist and began to taxi. Shortly thereafter, he experienced a loss of braking performance, which affected the airplane's steering capabilities, as steering is accomplished through differential braking and the brake system requires pneumatic pressure to operate. The pilot realized the compressed air supply valve was still shut off and attempted to turn it back on while turning the engine off and maintaining steering control. Due to the cockpit's size constraints, he could not reach the supply valve without unstrapping his seat belt and turning around. The airplane impacted a fence before he could do so, resulting in substantial damage to the left wing.
Investigation Findings
Further investigation revealed that the Yak-52 checklist does not require the pilot to check air pressure or the valve position during the preflight, engine start, or before takeoff phases. There was no noted preimpact mechanical malfunction that would have precluded normal operations.