What happened
On April 8, 2010, a Piper PA-34-220T, registration PT-WOO, was performing a ferry flight from Bacacheri to União da Vitória, Brazil. The aircraft was carrying a pilot and two passengers. During the landing on runway 17 at the União da Vitória Aerodrome, the pilot experienced a failure of the right brake system.
After an initial attempt to use the brakes resulted in a leftward yaw, the pilot managed to stabilize the aircraft and return to the centerline using differential engine power and rudder input. However, upon a second application of the brakes, the aircraft yawed sharply to the left. The pilot shut down both engines, but the aircraft could not be contained on the runway, eventually exiting the left side and colliding with a ditch. The impact caused significant damage to the left wing, radome, propellers, and the right landing gear strut.
The investigation
CENIPA investigators examined the wreckage and the brake assembly of the PT-WOO. The inspection revealed a small brake fluid leak at the right wheel. Investigators determined that one of the brake pads had detached from the backing plate because two rivets securing the pad had sheared. The backing plate itself was found to be warped, likely due to the loss of the pad.
The investigation also looked into maintenance practices. Mechanics at the maintenance facility reported that the shearing of these pins was a known issue and that, because the manufacturer only sold the complete brake assembly rather than individual pins, workshops often manufactured their own pins or reused old ones. Furthermore, the aircraft frequently operated on short, demanding runways, which placed intense stress on the braking system.
Findings
- The right brake failure was caused by the shearing of two rivets, which allowed a brake pad to detach from the backing plate.
- The aircraft's frequent operations on short runways required heavy braking, contributing to the premature fatigue of the components.
- The 100-hour inspection interval may have been insufficient to detect the progressive wear and degradation of the brake pins.
- The lack of availability of individual replacement pins from the manufacturer encouraged the use of non-standard, locally manufactured parts.
- The presence of a ditch on the side of the runway increased the severity of the aircraft damage.