Incident Overview
On September 6, 2020, at approximately 0905 Alaska daylight time, a Eurocopter AS350 B3, registration N354PA, was significantly damaged during an accident near Fort Greely, Alaska. The helicopter was operating under 14 CFR Part 91 as a ferry flight. The pilot and one crew member were not injured.
Flight Events
The pilot reported that while cruising at about 700 feet above ground level and 110 knots, a sudden loud bang occurred, accompanied by an uncommanded left yaw. The left passenger door had detached from the helicopter. During the separation sequence, the door impacted a main rotor blade, causing substantial damage. The pilot performed an emergency landing to a nearby grass area without further incident. The pilot noted that the door had not been used except for preflight security checks, which were conducted by both the pilot and a mechanic.
Maintenance and Service Bulletins
Airbus Helicopters had issued two Alert Service Bulletins (ASB) addressing sliding cabin door separations on AS350-B3 helicopters: ASB No. AS350-52.00.53 and ASB No. AS350-52.00.54. ASB No. AS350-52.00.53 mandated adding a label prohibiting pushing on the rear part of the rear support covers, following reports of cracked rear supports. Compliance was required within six months of the bulletin's issuance on June 18, 2020. ASB No. AS350-52.00.54 required inspection of the upper rail and roller of the sliding doors, with compliance due within 165 flight hours or 13 months and 6 days, whichever came first. Airbus reported 11 door loss events over 28 years, attributed to maintenance or operational errors. The operator stated that these service bulletins had not been complied with prior to the accident.
Post-Accident Examination
A Federal Aviation Administration aviation safety inspector examined the helicopter. The door rollers were displaced and not recovered; a partial slide piece on the lower rail was also missing. Door hinges appeared normal except where door slides had separated. Two witnesses confirmed the cabin door was closed before takeoff. Examination of the door revealed that the latches and locking finger were undamaged. The rubber seal around the door was perforated at the locking finger level. A cargo box in the cabin was positioned close to the door and showed white witness marks consistent with contact. The forward upper fitting rail was undamaged, but the lower forward fitting was deformed, the aft median rail showed deformation, and the lower rail exhibited interference. Airbus Helicopters noted that the damage pattern was consistent with the door lock being ineffective due to interference from the cargo box.