What happened
On October 1, 1995, at approximately 15:10, a Beechcraft BE-65-80, registration PT-BZS, crashed in a mountainous, heavily forested area near Turmalina, Minas Gerais. The aircraft had departed from Belo Horizonte for a flight to Turmalina. Approximately ten minutes into the flight, the aircraft was observed flying at a low altitude with one engine feathered. The aircraft subsequently struck trees, resulting in a post-impact fire and explosion. All five occupants—the pilot and four passengers—were killed, and the aircraft was destroyed.
The investigation
CENIPA investigators examined the wreckage and engine components to determine the cause of the engine failure and the loss of control. The investigation focused on the condition of both engines, the propeller mechanisms, and maintenance records. Investigators discovered that the left engine had suffered a significant loss of oil, with levels found at approximately 1.7 gallons. Notably, the oil used to top off the engine in Turmalina was identified as automotive gear oil (hypoid 90), which is inappropriate for aeronautical engines due to its high viscosity and lack of necessary high-temperature additives.
Analysis of the right engine revealed evidence of over-torque. The propeller assembly showed that the right propeller was at minimum pitch (maximum RPM) at the time of impact, and the impact was severe enough to tear one blade from the hub and fracture the reduction gearbox. The investigation also noted that the pilot had experienced a similar engine failure two days prior but had not reported the incident to the authorities.
Findings
- Deficient maintenance: The use of improper automotive gear oil led to insufficient lubrication and subsequent oil loss through the engine breathers.
- Inadequate supervision: The operator failed to properly oversee the maintenance of the aircraft's engines.
- Operational errors: The pilot proceeded with the flight despite being aware of the engine's precarious condition and previous failures.
- Flight indiscipline: The pilot failed to report a previous similar emergency, violating established safety protocols.
- Engine performance: The right engine was likely operating at a reduced power output due to over-torque and previous irregular operation, which rendered the aircraft unable to maintain single-engine climb performance in the mountainous terrain.