What happened
On April 5, 2018, a privately owned Rotorway Exec 162 helicopter, registration F-PFBJ, departed from Caromb for a flight to Eurre. During the flight, the aircraft was traveling at an airspeed of approximately 85 knots. At approximately 14:50 local time, the aircraft's trajectory curved upward, reaching an altitude of 1,505 feet before descending.
Witnesses on the ground observed the helicopter disintegrating in mid-air. The aircraft struck trees and the ground before catching fire. The impact resulted in one fatality and the total destruction of the aircraft.
The investigation
The BEA examined the wreckage found on a dirt path in a wooded area. Investigators noted that the main rotor mast was flexed under the rotor head and the low limits of both main rotor blades were crushed. Evidence of friction was found on the underside of one main rotor blade, and the tail boom had ruptured. The investigation established that the breakage of the tail boom was consistent with interference from a main rotor blade.
Further examination revealed that the cockpit doors and the plexigently canopy were destroyed in flight. The investigation also analyzed the pilot's recent flight experience, noting that while the pilot held a valid private license, they had only performed three hours of flight time in the three months preceding the accident.
Findings
- The aircraft was operating in light to moderate turbulence.
- The pilot was flying at a speed of approximately 85 knots, which exceeded the maximum recommended speed of 65 knots for turbulent conditions specified in the flight manual.
- The investigation determined that mast bumping occurred. This phenomenon was triggered when the pilot likely attempted to recover a level attitude following a rapid climb, leading to a sharp decrease in the load factor.
- This reduction in load factor allowed the rotor system to undergo excessive angular deflection, causing the main rotor blades to strike the tail boom and the airframe, leading to the structural failure of the aircraft.
- The flight manual lacked information regarding the mast bumping phenomenon or necessary recovery procedures, which may have contributed to the pilot's inability to manage the situation.