What happened
At approximately 0710 Pacific daylight time, a Bell 206B helicopter, registration C-GSLV, departed from a service landing area near Alice Arm, British Columbia. The aircraft was performing a routine crew change for a resource exploration site located roughly 6 nm to the north. While flying northeast across a tidal estuary under visual meteorological conditions, the helicopter crashed into the estuary approximately 0 and.5 nm from its departure point. The impact, characterized by a steep descent and a nose-down, left-side-low attitude, resulted in the destruction of the aircraft and three fatalities.
The investigation
Investigators examined the wreckage and the flight history of the aircraft. The pilot was experienced, with over 9,100 total flight hours, and there were no indications of fatigue, medical incapacitation, or engine failure. While the engine showed evidence of mud ingestion due to the impact, no pre-impact mechanical failures were found within the engine itself. The aircraft's weight and balance were estimated to be within safe limits for the flight.
Technical examination focused on the flight control systems and the main transmission. Investigators discovered that the right-hand pylon support spindle had fractured. Metallurgical analysis performed by the TSB Engineering Laboratory revealed that the fracture was caused by a progressive fatigue failure. This failure was traced back to a dimensional restoration repair previously performed on the spindle journal, which had introduced a stress concentration feature at the subsurface radius.
Findings
- The failure of the right-hand pylon support spindle in flight caused the helicopter to become uncontrollable and collide with the ground.
- A dimensional restoration repair on the spindle journal created a stress concentration that led to a fatigue crack and subsequent structural failure.
- The repair process for this critical component may have been conducted without sufficient original design data or verified stress analysis to ensure the part maintained its required integrity.
Safety action
Following the investigation, several regulatory actions were taken:
- Transport Canada issued Airworthiness Directives (AD CF-2007-02 and CF-2007-02R1) mandating the removal of specific Bell 206B pylon support spindles that had undergone certain repairs.
- Bell Helicopter Text тексту issued an Operational Safety Notice reinforcing opposition to these specific dimensional restoration repairs.
- The United States FAA issued a similar Airworthiness Directive to remove affected spindles from service.