What happened
During taxi operations for takeoff, an aircraft experienced a sudden loss of brake pressure. The pilot reported that the brakes failed to function when applied to slow the aircraft during a turn following a back-taxi maneuver on the runway. As a result, the airplane traveled off the side of the runway and continued down a slope into a ditch, where it eventually rolled onto its right wing. The pilot was not injured.
The investigation
The investigation focused on the functionality of the braking system. According to the pilot, the parking brake had been applied while the aircraft was being fueled, and the brakes had operated correctly during both that period and the subsequent engine run-up.
Investigators found no evidence of brake fluid leaks on the hangar floor where the aircraft was stored, nor was any fluid detected along the taxi route used by the aircraft. Upon disassembly, the master brake cylinder appeared to be in working order and showed no signs of leaking. Notably, the aircraft featured a placard required by Airworthiness Directive 85-02-05 R1, which warns: "NO BRAKING WILL OCCUR IF AIRCRAFT BRAKES ARE APPLIED WHILE PARKING BRAKE HANDLE IS PULLED AND HELD."