What happened
On December 30, 2014, a Beechcraft N3 and registration PT-BQD departed from the Fazenda Bandeirantes aerodrome in Aquidauana, Mato Grosso do Sul, bound for the Estância Teruel Ipanema aerodrome in Campo Grande. The aircraft was operating a private flight with a pilot and one passenger on board.
Approximately fifteen minutes into the flight, while cruising at 5,500 feet, the pilot observed a drop in engine oil pressure, followed by significant vibration and an increase in propeller RPM. Shortly thereafter, the engine seized. The pilot was forced to perform an emergency landing in a field in the municipality of Aquidauana. While the aircraft sustained substantial damage to the engine, landing gear, fuselage, and right wing, both occupants emerged from the crash uninjured.
The investigation
CENIPA investigators examined the Continental IO-520-BB(6) engine, which had recorded 842 hours and 08 minutes since its last overhaul and 13 hours and 20 minutes since its last annual inspection. Physical evidence, including a hole in the upper part of the left engine crankcase near cylinder 6, indicated a severe internal failure.
Following a teardown at an ANAC-certified workshop, the engine was analyzed by specialists from the Institute of Aeronautics and Space (IAE). The investigation established that the failure originated in either cylinder 5 or cylinder 6. Investigators identified the failure of the bolts that secure the connecting rods of these cylinders to the crankshaft. However, because several fragments of these bolts were not recovered during the disassembly, the exact primary cause could not be definitively determined.
Findings
- The engine failure was triggered by the breakage of the bolts connecting the connecting rods to the crankshaft in cylinder 5 or 6.
- Potential causes for the bolt failure include excessive bearing clearance, breakage of the rod cap bolt, or loss of nut torque, all of which could lead to excessive clearance between the rod cap and the crankshaft journal.
- Aircraft maintenance was identified as a contributing factor, specifically regarding the possibility of reusing mandatory replacement parts during the overhaul or improper torque application and bearing seating during the engine's final assembly.