What happened
On September 26, 2014, a flight instructor and a pilot conducted a proficiency check flight in an Airbus EC 12/0B, registration HB-ZGJ, departing from Lodrino. The flight was intended to renew the pilot's type rating. After performing standard maneuvers, the crew proceeded to the San Vittore airfield to practice emergency procedures, specifically simulated hover autorotations.
During the final maneuver of the session, the aircraft was hovering at an altitude of approximately 0.8 to 1 meter. As the instructor applied the twist grip to simulate the end of the autorotation, a discrepancy in the execution of the maneuver occurred. The instructor reported that the pilot applied a rapid and heavy upward movement on the collective without a prior descent. This caused the helicopter to climb to an altitude of 1.5 to 2 meters while the rotor RPM began to decrease. The instructor intervened by adjusting the twist grip and taking control to land the aircraft safely.
The investigation
The investigation focused on the mechanical and operational aspects of the torque excursion. Upon landing, the crew observed an "over limit detected" warning on the Vehicle and Engine Multifunction Display (VEMD). A subsequent review of the VEMD data revealed that the torque had exceeded the maximum transient rating of 110%, reaching a peak of 139% for a duration of two seconds. The investigation also noted that the crew did not hear any audible warnings during the event. Following the incident, the aircraft's drivetrain was inspected for damage, and maintenance providers and the manufacturer were involved in the technical analysis.
Findings
- The primary cause of the incident was an uncontrolled and rapid application of the collective lever during the transition from a simulated autorotation to a powered hover.
- The pilot's input resulted in a torque excursion of 139%, significantly exceeding the 110% transient limit.
- The maneuver caused damage to the entire drivetrain of the Airbus EC 120B.
- The crew did not perceive any acoustic warning during the over-torque event.