What happened
On January 31, 2011, a Piper PA-25-235 agricultural aircraft, registration PT-BII, departed from a private airstrip at Fazenda Bananal in Miracatu, São Paulo, to perform aerial spraying operations. During the flight, the pilot experienced intense vibrations centered in the aircraft's empennage. Unable to maintain level flight, the pilot attempted an emergency landing on the nearby SP-193 highway.
During the landing sequence, the aircraft's right wing struck a traffic sign. This impact caused the aircraft to veer off the roadway and undergo a nose-over (pilonamento). The aircraft sustained substantial damage to the fuselage, wings, empennage, engine, and landing gear. The pilot was uninjured.
The investigation
CENIPA investigators examined the engine components following the accident. Upon disassembly, the investigation revealed that the crankshaft was fractured near the counterweights. Subsequent analysis by a certified facility determined that the part number of the installed counterweights did not match the specifications required for that specific engine model.
Further investigation into the engine's maintenance logs during its last overhaul showed no record of compliance with Lycoming Service Instruction 1143B. This instruction specifically addresses the rectification of counterweight bushings. The investigation established that failure to follow this service instruction renders the counterweights ineffective at absorbing engine-generated vibrations.
Findings
- The installation of incorrect crankshaft counterweights for the engine model.
- Failure to comply with Lycoming Service Instruction 1143B during engine maintenance.
- Inadequate maintenance oversight regarding the verification of parts and maintenance records following engine overhauls.