Eurocopter BK 117 C-2, Albert Lea, Minn., Jan. 1, 2011–The NTSB found the pilot’s inadequate preflight inspection of the engine cowling latches resulted in the opening of the cowling door in flight and subsequent damage to the main rotor blades. The pilot told investigators that he had completed a preflight inspection at the beginning of his shift, but then at the request of a mechanic he verified the fuel control settings on the helicopter, which required opening the engine cowling doors. The pilot said that before the flight he visually checked the doors and latches, but after starting the number-one engine, the flight medic reported hearing an unusual sound. He asked her to check the security of the cowling door latches and she reported they seemed to be secure. Half a mile from the destination helipad, the pilot heard a loud bang and thump from the rear of the helicopter and vibration set in. He landed at the destination, and examination of the rotor revealed substantial damage to all four main blades, while the lower portion of the left engine cowling door was missing.

Bell 222U, Santa Maria, Calif., April 9, 2010–The pilot’s inadequate preflight inspection failed to ensure that all tiedown straps were removed before takeoff, according to the NTSB. The pilot was dispatched around 1 a.m. for a patient pickup and during the walkaround inspection in the dark he saw a flight-duty nurse head to the opposite side of the helicopter. The pilot told investigators that he assumed the nurse had untied the tail-rotor tiedown strap, so he removed only the main rotor tiedown. Upon engine start up, the tail-rotor tiedown strap broke, causing damage to a tail rotor blade and the pitch-change links. Unaware, the pilot flew to the destination and picked up a patient. During the loading process, a flight nurse noticed strap material wrapped around the tail-rotor driveshaft. The pilot shut down the engine and helped the nurse remove the material. The pilot then flew the patient to the next hospital, where inspection revealed damage to the tail rotor. The company’s director of maintenance ruled the helicopter unairworthy with a compromised flight control system.

Contributing to the accident was the pilot’s improper management of sleep opportunities during the preceding rest period, which likely contributed to fatigue. Despite the awareness that he was on duty for a night-time shift, the pilot stayed awake for 15 hours before going to sleep around 11 p.m. that evening. He had gotten just two hours of rest before being awakened for the mission.