Pilot Report
The pilot of a helicopter emergency medical services (HEMS) flight reported that he had conducted a pre-flight inspection at the start of his shift. Earlier in the day, prior to the accident flight, he verified some fuel control settings at the request of a mechanic. Both of these inspections required opening the engine cowling doors. Before the accident flight, the pilot visually checked for security of doors and cowlings, leaking fluids, tie-downs, and the overall condition of the aircraft.
After starting the number one engine, the flight medic heard an "unusual rattle." The pilot asked her to check the security of the cowling door latches. The medic reported that the latches appeared secure. The flight proceeded without incident until about one-half mile from the destination helipad, when the pilot heard a "loud bang and thump from the rear of the aircraft." A "four per rev" vibration developed. The pilot considered that something might have separated from the rotor system due to the noise and vibration. He continued the approach and landed without further incident.
Post-Accident Examination
A post-accident examination revealed substantial damage to all four main rotor blades. The lower portion of the left engine cowling door had separated and was not recovered. No anomalies were observed with regard to the airframe side of the cowling door latches. At the time of the accident, the helicopter was being repositioned to pick up a patient, and only the pilot and medical crew were on board.