Accident Overview
During the landing roll, the pilot was unable to maintain directional control, causing the airplane to swerve side-to-side before departing the right side of the runway.
Pilot Report and Brake Condition
The pilot stated that overhauled brake assemblies had been installed prior to the accident. He reported that the brakes felt "spongy" and that the pedals went "almost to the floor, requiring two or three additional pumps for a hard pedal." The pilot was informed that this condition was "normal" because the airplane was not equipped with power brakes or anti-skid.
Maintenance Findings
The brake assemblies were removed and sent to the overhaul facility for examination. Inspectors found that both brake assemblies each had one return mechanism binding. The return mechanism featured a self-adjusting friction bushing designed to slip along the return pin at a predetermined spring pressure. When brake pressure was applied, the pressure plate extended toward the number one rotor, pulling the return pins through the swage and tube assemblies and compressing the return springs. Although the swage was intended to move through the tube freely, one swage on each brake was not moving as designed.
Additional Observations
The investigation noted that the brake travel was greater than normal because the "normal travel" setting had never been established. The binding of the return mechanisms likely prevented proper brake operation, contributing to the pilot's inability to maintain directional control.
Conclusion
The binding of the return mechanisms in both brake assemblies, combined with the absence of a properly set normal brake travel, resulted in the loss of directional control during the landing roll and the subsequent runway excursion.