What happened
While performing aerial surveillance of a fishing dispute near Tabusinterc, New Brunswick, an AS350-B3 helicopter, registration C-FMPH, experienced a sudden cockpit alarm and the illumination of a red GOV warning light. During a right turn at 700 feet, the pilot attempted a precautionary landing toward the shore. Following the warning, the rotor rpm increased beyond maximum limits, triggering intense vibrations throughout the aircraft.
In an attempt to manage the situation, the pilot reduced the twist grip throttle and lowered the collective; however, the rotor rpm continued to rise. Believing manual throttle control was lost, the pilot moved the throttle back to the "FLIGHT" detent and attempted to switch the fuel control mode to manual, but the vibrations prevented the switch from being properly engaged. The aircraft entered a rapid descent. After landing, the pilot experienced ground resonance and performed a second landing before eventually shutting down the engine using the fuel shut-off lever. The pilot and two passengers exited the aircraft without injury.
The investigation
Investigators examined the engine's digital engine control unit (DECU) and the hydro-mechanical unit (HMU). While the HMU was found to be within functional limits, testing of the DECU by the manufacturer revealed that an internal component, an optocoupler, failed at approximately 70°C, which triggered the red GOV light.
The investigation also reviewed the pilot's training history. The pilot had significant experience in other helicopter types but had received limited in-flight emergency training specifically for the AS350-B3's FADEC system. Furthermore, the investigation found that the pilot's recent recurrent training was conducted on an AS350-B, a model lacking the complex electronic fuel management system present in the B3.
Findings
- The red GOV light was caused by a malfunction in the DECU's internal optocoupler.
- The pilot mishandled the emergency because they were unaware that the twist grip throttle still provided manual fuel flow control during a GOV light event.
- The pilot's actions—specifically reducing the collective and throttle simultaneously during a descending turn—masked the effect of the throttle adjustment, leading to the rotor overspeed.
- The pilot had not received sufficient in-flight emergency training for the specific FADEC/governor failure procedures on the AS350-B3.
- A lack of required proficiency or competency checks within the operator's manual meant there was no mechanism to detect the pilot's training deficiencies prior to the accident.