Incident Overview
During a dual instructional flight, the instructor and student pilot identified a left brake failure while taxiing for takeoff. The instructor attempted to steer the aircraft using asymmetric engine power, but was unable to control the turning motion. The aircraft subsequently ran off the edge of the taxiway and came to rest in a ditch.
Post-Accident Findings
Following the accident, examination revealed that the left brake master cylinder was empty of hydraulic fluid. The cause of the fluid loss was a failed 'O' ring within the master cylinder, which allowed hydraulic fluid to escape into the right brake system. No other failures or system anomalies were reported.
Aircraft and Flight Details
The flight was a dual instructional sortie. Specific aircraft type, registration, operator, date, location, and number of occupants were not provided in the source material. No information regarding injuries or damage extent is available beyond the aircraft's entry into the ditch. No weather conditions or air traffic control involvement were mentioned.
Conclusion
The investigation identified a mechanical failure of the 'O' ring in the left brake master cylinder, leading to loss of brake fluid and subsequent inability to maintain directional control during taxi. The asymmetric power technique employed by the instructor was insufficient to overcome the brake failure.