What happened
On January 1, 2009, an AT-6D aircraft, registration PT-LDO, departed from Campo de Marte (SBMT) as part of a formation flight destined for Santos Dumont (SBRJ). While cruising at 5,500 feet under visual flight rules, the pilot detected engine vibrations approximately 15 minutes after takeoff. Upon determining that insufficient power remained to maintain level flight, the pilot initiated an emergency procedure to land on a small, unpaved grass strip used for ultralights.
During the landing roll, the aircraft exceeded the boundaries of the grass runway and traveled 100 meters beyond the opposite end. The aircraft encountered uneven terrain consisting of ditches filled with water and mud due to the summer rainy season, causing the aircraft to nose over. The aircraft ended up in an inverted position, and the pilot was unable to exit the cockpit without external assistance because the mud and water levels had risen near the canopy. The pilot remained uninjured.
The investigation
CENIPA investigators examined the engine components at the Institute of Aeronautics and Space (IAE). Technical analysis revealed that the failure was caused by the failure of connecting rod number 9. The investigation established that the failure originated from material fatigue, which likely began at corrosion pits.
Investigators also reviewed the pilot's decision-making regarding the landing configuration. While the aircraft's technical manuals for unprepared terrain recommended landing with the landing gear retracted to mitigate impact, the pilot chose to extend the gear, likely in an attempt to minimize damage to the airframe. Additionally, the investigation looked into the maintenance history, noting that the engine had undergone a restoration process using reconditioned parts due to the scarcity of new components at the time.
Findings
- Engine fatigue: The primary cause of the engine failure was the failure of a connecting rod due to fatigue and corrosion pits.
- Maintenance and supervision: The engine maintenance involved a manual restoration process, and the operator had not implemented more rigorous inspections to detect fatigue or corrosion in critical components.
- Pilot judgment: The pilot's decision to extend the landing gear during the forced landing on unprepared terrain contributed to the severity of the accident.
- Aircraft damage: The AT-6D sustained severe damage to the engine, propeller, landing gear, and empennage.