What happened
On a morning news-gathering flight over the Montreal metropolitan area, a Robinson R44 II helicopter, registered C-GDSF, experienced a critical mechanical failure while flying near the Champlain Bridge. The aircraft, operated by Groupe TVA Inc., was performing a routine mission to transmit television images when the rotor speed dropped below safe operating limits.
As the rotor speed decreased, the pilot notified air traffic control of an emergency landing at Mel's Studios. During the descent, the pilot attempted a 180-degree turn, but the aircraft's control response became increasingly sluggish. The helicopter ultimately struck a ditch between the studio and the Bonaventure Expressway, landing heavily on its side. The crash resulted in two serious injuries for the pilot and the reporter on board.
The investigation
Investigators examined the wreckage and flight data, including radar, voice recordings, and onboard video. While no physical defects were found in the engine or rotor components, the investigation focused on why the rotor speed (Nr) decayed so rapidly.
Technicians discovered that the Clutch/Start circuit breaker had tripped. The investigation explored whether this occurred due to pilot action or impact, but ultimately focused on a hypothesis where the breaker tripped in flight due to a temporary overvoltage. Because the breaker powers both the clutch actuator and the associated warning light, its activation left the pilot without visual or auditory notification that the belt tensioner had ceased functioning. This prevented the pilot from realizing the clutch was no longer engaged until the low rotor RPM horn sounded.
Findings
- The primary cause of the accident was the tripping of the Clutch/Start circuit breaker, which led to a reduction in rotor speed.
- The malfunction occurred at a low altitude, providing the pilot with insufficient time to execute a proper autorotation.
- The pilot's inability to detect the failure early was exacerbated by the fact that the breaker also powers the clutch warning light, leaving no visual indicator of the malfunction.
- The investigation noted that the pilot's recent recurrent training was not as frequent as required for commercial operations, which may have impacted the execution of the emergency maneuver.
- The design of the electrical system allowed a single breaker to control both an essential flight component and non-essential systems, increasing operational risk.