What happened
On September 19, 2007, an AS 365 N3 helicopter, registration PR-RFF, was positioned at the Helibras helipad in Itajubá, Brazil, for a delivery flight following maintenance and painting services. During the engine start sequence, specifically after the completion of the right engine start cycle, the aircraft suddenly tilted forward and to the left. This movement caused the main rotor blades to strike the ground, leading the helicopter to rotate approximately 180 degrees and eventually come to rest on its left side.
The impact caused severe damage to the main rotor, the right engine, the main transmission, and the left stabilizer. The main rotor blades were destroyed upon contact with the ground. While the pilot escaped without injury, the co-pilot and a mechanic standing outside the aircraft sustained minor injuries.
The investigation
CENIPA investigators examined the aircraft's maintenance history, the crew's operational procedures, and the mechanical design of the flight controls. The investigation focused on the cockpit procedures used during the start sequence and the physical state of the collective pitch control.
Investigators discovered that the crew was using a condensed checklist created by the pilot rather than the official manufacturer's Flight Manual. This custom checklist omitted critical warnings regarding the neutral position of the cyclic and the necessity of securing the collective pitch control before starting an engine. Furthermore, the investigation analyzed the mechanical design of the collective pitch locking mechanism, which was found to be susceptible to a specific failure mode.
Findings
- False Locking Mechanism: The design of the collective pitch locking pin allowed for a "false lock," where the pin rests on a protrusion on the locking plate. This condition is difficult for pilots to identify visually and can lead to the control unexpectedly releasing under load.
- Inadequate Procedures: The crew utilized an unauthorized, abbreviated checklist that lacked essential safety warnings and required checks found in the official Flight Manual.
- Human Factors: The investigation identified elements of complacency and overconfidence among the crew, driven by their extensive flight experience. This led to a disregard for standardized procedures and a reliance on informal operational culture.
- Lack of Oversight: The absence of a dedicated Flight Safety department within the organization contributed to a lack of standardized operational doctrine and insufficient management supervision.
- Crew Coordination: At the moment of the uncontrolled movement, neither pilot was actively guarding the flight controls, as both were focused on post-start tasks.