What happened
On a return flight from Prince Rupert to a logging camp near Kumealon Inlet, a Robinson R22 helicopter, registration C-FILW, experienced a catastrophic in-flight breakup. The aircraft, operated by Bear Creek Contracting Ltd., was being used by the logging manager for private transport. While the initial leg of the flight had been smooth, the aircraft disappeared during its return trip. A search operation located the wreckage in a forest near the intended destination a day later.
The pilot sustained fatal injuries during the structural failure, and the wreckage showed significant damage consistent with a mid-air disintegration. At the time of the accident, approximately 1240 Pacific standard time, local weather conditions included significant turbulence. Nearby crews in a Boeing 107 reported severe atmospheric instability and winds reaching 30 to 40 knots, describing the turbulence as powerful enough to displace liquids within a cockpit.
The investigation
Investigators examined the wreckage and the surrounding environment, noting that while tree branches above the crash site were damaged, there were no evidence of main-rotor blade strikes on the trees themselves. The debris trail and the state of the airframe indicated the aircraft broke apart while still airborne.
Technical analysis focused on the rotor system. Evidence showed that a powerful downdraft caused the rotor system to unload, leading to excessive movement that damaged the droop stops and aluminum brackets. The investigation established that the elastomeric bumpers failed, allowing the rotor to teeter with enough force to overload the pitch change rod. This failure led to the separation of one of the two main-rotor blades after a coning hinge bolt broke under extreme loads.
Findings
- The helicopter encountered severe turbulence that unloaded the main-rotor system, causing mechanical damage that rendered the aircraft uncontrollable.
- The resulting forces caused a coning hinge bolt to fail, leading to the separation of a main-rotor blade.
- The massive imbalance created by the loss of the blade caused the transmission to shift violently, deforming the airframe and the cabin firewall.
- The structural deformation caused the pilot's restraint system to loosen, resulting in the pilot being ejected from the cabin.
- The operator had exceeded the service life limits for the freewheel unit sprag clutch by more than 700 hours.
- The operator continued to fly the aircraft despite certain components having exceeded their operational life limits.