What happened
The pilot reported that the approach and touchdown were conducted normally. However, as he began to apply wheel brakes to slow the aircraft on the runway, the right brake system failed to function. To prevent the aircraft from departing the end of the runway and striking trees located in the vicinity, the pilot intentionally applied significant pressure to the left brake pedal. This action caused the aircraft to pivot sharply, resulting in a ground loop.
The investigation
Following the incident, mechanics performed a detailed disassembly of the right master brake cylinder to determine the root cause of the failure. Inspection of the internal components revealed that one of the O-rings within the cylinder assembly had fractured into two distinct pieces. This structural failure of the sealing component likely prevented the hydraulic system from building or maintaining the necessary pressure on the right side.
Findings
The investigation identified a mechanical failure in the braking system as the primary factor. Specifically, the broken O-ring within the right master brake cylinder resulted in the loss of braking capability on that side. The pilot's decision to use asymmetric braking was a direct response to the emergency situation to avoid a more severe collision with obstacles at the runway end.
Safety message
Regular maintenance and inspection of hydraulic brake systems are critical for flight safety. Ensuring that all seals and O-rings are intact during routine checks can prevent sudden loss of braking power during critical phases of flight such as landing and rollout.