What happened
On February 22, 2012, an AS350-BA helicopter, registration PT-YAK, was conducting a flight as part of the 2012 Carnival Operation near Marituba, Pará. Approximately 10 minutes after departing from the GRAESP base, while cruising at 600 feet, the crew experienced a strong vibration and identified a surge in the main rotor rotation.
The crew performed emergency procedures to reduce the main rotor rotation and executed an emergency landing in a barren area near the BR-316 highway. During the landing phase, the aircraft exhibited aerodynamic behavior consistent with ground resonance. The resulting vibrations caused substantial damage to the aircraft's cabin, tail boom, tail rotor activation tree, and starflex. The two crew members sustained minor injuries, while the two passengers were uninjured.
The investigation
CENIPA's investigation focused on the mechanical failure and the maintenance environment. Investigators established that the Fuel Control Unit (FCU) had been contaminated with water. This contamination was linked to the transport of fuel in inadequate containers when operating away from the main base, as well as a lack of standardized procedures for fuel testing during refueling.
Furthermore, the investigation examined the maintenance history of the aircraft. It was found that recent maintenance and dynamic balancing of the main rotor blades had been performed in a manner that did not comply with manufacturer-prescribed criteria. The investigation also identified that several components installed in the main rotor head lacked proper traceability, calling the airworthiness of the aircraft into question.
Findings
- Fuel contamination in the FCU was a primary driver of the rotor rotation surge.
- Maintenance of the main rotor blades was performed outside of manufacturer-prescribed limits, which aggravated the ground resonance event.
- An organizational culture prioritized operational missions over flight safety, leading to the omission of critical maintenance inspections and fuel testing.
- The maintenance provider faced high-stress conditions and a shortage of qualified personnel, which contributed to the failure to identify fuel contamination and improper component installation.
- The first officer was operating with an expired technical qualification certificate.
- Several components in the rotor head lacked verifiable traceability.