Aeronca 15AC N1337H accident near Pontiac, Michigan

Probable cause

The improper installation of the left wheel brake torque plate by maintenance personnel, which resulted in the separation of the torque plate from the axle endplate and a loss of directional control during landing.

NTSB analysis

The private pilot was concluding a local flight in the tailwheel-equipped airplane. After numerous uneventful touch-and-go landings, the pilot attempted a full-stop landing when the airplane suddenly swerved to the left shortly after touchdown. The pilot attempted to regain directional control by applying right rudder and increasing engine power for an aborted landing; however, the airplane swerved to the right and collided with a snowbank next to the runway. The airplane sustained substantial damage to both main wing spars and the rudder.

A postaccident examination revealed that the left wheel brake torque plate had separated from the landing gear axle endplate, which allowed the brake assembly to rotate with the brake disk that was attached to the wheel. The airplane had been modified with Cleveland wheels and brakes through a supplemental type certificate (STC). However, additional examination of the brake torque plates revealed that they had not been installed in accordance with the STC installation instructions. Specifically, the torque plates were not modified with two 0.25-inch holes that were required to ensure proper alignment with the landing gear axle endplate, and improperly sized bushings had been used during the installation. The improper torque plate installation allowed for movement of the torque plate and unintended transverse loading of the anchor bolts, which resulted in the fracture of the anchor bolts that secured the left brake torque plate to the axle endplate. The failure of the left brake likely caused the loss of directional control during landing.

Text from the NTSB. Open the NTSB docket for CEN17LA070 for the full record.