Cessna 170B N170HT accident near Cameron Park, California

Probable cause

A failure of the right brake master cylinder piston due to a faulty return spring, which resulted in a seized right main landing gear brake and a runway excursion

NTSB analysis

The pilot was landing at his destination airport when the airplane veered to the left after touchdown. . The pilot attempted to correct the movement and turn the airplane back to the runway centerline with the addition of power and right rudder inputs, but the airplane then veered to the right and departed the right side of the runway.

The pilot did not recall experiencing any mechanical anomalies with the brakes during the accident flight and observed normal resistance during the landing. Postaccident examination of the brake system revealed that the right brake master cylinder failed to release pressure twice during testing and the piston had to be manually lifted before the cylinder would release pressure, which the pilot was unlikely to have been able to do during landing. The seized brake master cylinder was likely due to a deformed return spring that had bowed at some point during its service life. The manufacturer reported that the failure of the cylinder to release pressure would have resulted in a locked brake.

Although the pilot could not recall if he applied brakes, both his and the witness’ recollection that the airplane abruptly turned right and departed the runway suggests that he may have applied right brake as the airplane was veering left. During this time the piston likely failed to release pressure due to the faulty return spring, which resulted in a runway excursion.

Text from the NTSB. Open the NTSB docket for WPR24LA045 for the full record.