What happened
On May 4, 2018, a PZL-SW4 helicopter, registration PP-MHJ, was performing a passenger transport flight from Curitibanos Aerodrome (SSKU) to Porto Belo Aerodrome (SDEN) in Santa Catarina, Brazil. Approximately ten minutes into the flight, while cruising at an altitude between 600 and 1,000 feet AGL, the pilot and four passengers heard a loud noise.
Following the noise, the pilot initiated an autorotation procedure and landed the aircraft in an open cornfield. While the pilot and all four passengers escaped without injury, the aircraft sustained substantial damage. The impact during landing also caused damage to the outer portions of the main rotor blades, the tail cone, and the horizontal stabilizer.
The investigation
CENIPA investigators focused on determining the source of the loud noise and the subsequent loss of power sensation. Extensive testing was performed on the Rolls-Royce M250-C20R/2 engine. Laboratory analysis of fuel and oil samples showed no evidence of contamination, and bench tests of the engine, including pneumatic lines and chip detectors, revealed no mechanical abnormalities or internal failures. The aircraft was also confirmed to be within its specified weight and balance limits.
Investigators examined the transmission fairing on the right side of the aircraft and discovered a fracture in the door, aligned with the path of the main rotor blades. The examination of the locking latches showed no significant damage or failure of the hardware itself. The investigation concluded that the door had been left in a position that allowed it to open during flight, leading to the collision with the rotor blades.
Findings
- The primary cause of the noise and subsequent emergency procedure was the insecurely closed transmission fairing door, which opened in flight and was struck by the main rotor blades.
- An attitude of complacency during the pre-flight exterior check likely led the pilot to fail to verify that the fairing latches were properly secured.
- The pilot's judgment contributed to the severity of the event, as an inadequate assessment of the aircraft's controllability led the commander to disregard a precautionary landing with a normal approach in favor of an immediate autorotation.
- The damage to the tail cone and horizontal stabilizer was attributed to an involuntary or excessive movement of the cyclic control during the landing phase.