Incident Details
The airline transport pilot reported that at the start of his second flight of the day, the airplane's brakes appeared to be locked, despite the parking brake not being set. He was able to unlock the brakes by manipulating the parking brake several times, applying engine power, and moving the nose gear steering via the rudder pedals several times. The brakes released, but he did not report the brake problem to the operator.
While landing at the end of the third flight, as soon as all three landing gear tires were on the ground, the airplane began a gradual right turn. The pilot applied left brake and left rudder with minimal effect. The left main landing gear tire produced a skid mark on the runway as the airplane overshot the planned taxiway exit, and then departed off the right edge of the runway. The airplane received structural damage to the fuselage and wing spars.
Examination Findings
The airplane was equipped with hydraulic brakes and a hydraulic parking brake valve. The parking brake valve is activated by a cable between the valve and the parking brake handle. Setting the parking brake involves applying brake pedal pressure and then pulling out on the parking brake handle.
After recovery from the ditch, an FAA inspector, accompanied by a mechanic from the operator, examined the airplane. Their examination revealed that the parking brake cable was not securely fastened to the airframe by its attaching clamp. This could allow the outer cable housing to move independent of the inner wire attached to the parking brake valve, and could prevent parking brake release. Partial valve activation could hold hydraulic brake pressure on the airplane's brakes, if the brakes were touched during flight.