Maule M 7-235C N6447M accident near Klamath Falls, Oregon

Probable cause

The pilot's failure to follow the pre-takeoff checklist and the failure of the left main landing gear brake due to a damaged brake master cylinder piston rod, which resulted in a stuck left brake and subsequent loss of control during the landing roll.

NTSB analysis

The commercial pilot reported that he did not note any drag or restrictions from the wheel brakes during taxi or takeoff. When the airplane touched down at the destination airport, it immediately began to veer left. The pilot was unable to overcome the uncommanded movement despite his application of right rudder and right brake, and the airplane nosed over and came to rest inverted.

The pilot reported that as he was preparing the airplane for the flight, he removed the chocks and the airplane started to roll backwards. He assumed that his son had released the parking brake and replaced the downhill chocks the night before the accident when he finished washing the airplane. The pilot completed the preflight but did not follow the checklist to confirm that the parking brake was disengaged before departing on the flight. Postaccident, the brake knob was found in the ON (engaged) position. However, the pilot reported the absence of any drag during ground operations indicating that the parking brake may not have been engaged before taking off, which can occur if the toe brakes are not fully extended when the parking brake is set.

Postaccident testing revealed that the left brake became stuck multiple times due to the interference of circumferential gouges and ridges on the left brake master cylinder piston rod and bushing, which likely resulted from normal operation of the parking brake. Because the parking brake knob was in the ON position during the flight, the left brake could have been set by depressing the toe brake. The rod damage would have then prevented the free travel required for the piston to release brake pressure and disengage the left brake, thereby causing the airplane to veer left after touching down. Although a visual inspection of the rod could have detected the wear, review of the maintenance logs since 2010 showed that the master cylinder had not been disassembled and inspected, nor was it required to be.

Text from the NTSB. Open the NTSB docket for WPR17LA192 for the full record.