What happened
On August 27, 2014, a Beechcraft F33A, registration PT-JRY, departed from Marília, SP, bound for Franca, SP, carrying a pilot and two passengers. Approximately ten minutes into the flight, while cruising at 550 feet, the engine began operating irregularly, characterized by significant vibration, smoke, and a loss of power.
In response to the engine failure, the pilot reduced power and performed an emergency landing in an unprepared field near Pirajuí, SP. The aircraft struck a contour line in the terrain during the landing. The impact resulted in substantial damage to the aircraft. The pilot escaped without injury, while the two passengers sustained minor injuries.
The investigation
CENIPA investigators examined the engine, a Continental Motors IO-520-BA, and performed a bench analysis of its components. Upon inspecting the engine cowling, investigators discovered a hole in the engine casing. Further disassembly revealed that the connecting rod of cylinder number 3 had broken and undergone a melting process.
Technical analysis focused on the engine's stud assembly and sealing methods. Investigators found that the engine was using an outdated stud design. While Continental Motors had issued Service Bulletin M77-9 in 1977 to modify these studs to prevent torque loss and subsequent bearing wear, there was no record in the engine logbook indicating that this modification had been implemented on PT-JRY.
Additionally, investigators found that sealant wire had been used to close the engine block and around the bearings. This practice, which was not recommended by the manufacturer, facilitated relative movement between the engine halves. This movement caused the bearings to shift, obstructing the oil passages and leading to insufficient lubrication.
Findings
- The primary cause of the engine failure was inadequate maintenance, specifically the failure to implement Service Bulletin M77-9, which left the engine susceptible to torque loss in the studs.
- The use of non-recommended sealant wire contributed to the misalignment of oil passages, leading to the melting of the connecting rod due to overheating.
- The decision to land with the landing gear in the extended position on sandy, irregular terrain may have increased the severity of the aircraft damage.
- Organizational processes regarding maintenance oversight were identified as a contributing factor.