What happened
On July 11, 2012, a Robinson R22 helicopter, registration PT-HOL, was conducting a flight training mission near the Guarapiranga dam in São Paulo, Brazil. The flight, operated by Go Air / Master Escola de Aviação Civil Ltd., included an instructor and a student.
During the return leg to Campo de Marte Aerodrome, approximately 2.7 nautical miles from the destination, the crew experienced a sudden loss of power and difficulty maintaining directional control at an altitude of approximately 500 feet AGL. The aircraft struck the roof of an industrial warehouse, which caused the tail section to separate. The main fuselage continued through the roof and impacted the ground. The impact destroyed the aircraft, and both pilots sustained fatal injuries.
The investigation
CENIPA's investigation focused on the mechanical integrity of the power unit. While the engine was found to be functioning normally without fuel or carburetion issues, investigators identified a catastrophic failure in the power transmission assembly.
Technical analysis revealed that the power transmission shaft (Part Number A166-1) had broken due to a fatigue mechanism. This fatigue was initiated by corrosion within the fixing hole where the shaft meets the yoke (Part Number A907-4). The investigation found that the maintenance performed on this specific coupling was inadequate. Specifically, the failure to follow the manufacturer's installation instructions regarding the use of approved primers and application methods facilitated the development of fretting and corrosion.
Findings
- Maintenance inadequacy: The primary cause of the accident was the failure of the power transmission shaft due to fatigue, driven by corrosion and fretting caused by improper maintenance procedures.
- Improper materials: The use of non-aeronautical products or incorrect application of primers in the junction between the shaft and the yoke contributed to the structural degradation.
- Managerial oversight: The technical inspector failed to identify that maintenance procedures were deviating from the Robinson Helicopter Company manual, and the operator had processed conflicting technical data regarding manufacturer communications.
- Pilot factors: The investigation noted that the degraded flight conditions and loss of rotor rotation made aircraft control extremely difficult, and an inadequate assessment of a landing site may have contributed to the severity of the impact.