Eurocopter Deutschland Gmbh MBB-BK 117 C-2 N145SM accident near Albert Lea, Minnesota

Probable cause

The pilot's inadequate preflight inspection of the engine cowling latches prior the flight, which resulted in the cowling door opening in-flight and striking the main rotor blades.

NTSB analysis

The pilot said that he completed a preflight inspection at the beginning of his shift. He noted that earlier in the day, prior to the accident flight, he verified fuel control settings at the request of one of the mechanics. Both of these required that the engine cowling doors be opened. The pilot stated that prior to the accident flight, he visually checked the security of doors and cowlings, leaking fluids, tie downs, and the overall condition of the aircraft. He reported that after starting the number one engine, the flight medic commented that she heard an unusual sound. He subsequently asked her to check the security of the cowling door latches. When the flight medic returned, she informed him that the latches appeared to be secure. He stated that the flight proceeded without incident until about 1/2-mile from the destination helipad, he heard a loud bang and thump from the rear of the helicopter. Shortly thereafter the helicopter started to vibrate and he thought that the noise and vibration might be something from the rotor system. He elected to continue the approach to the destination helipad and subsequently landed without further incident. A postaccident examination revealed substantial damage to all four main rotor blades. The lower portion of the left engine cowling door was separated. No anomalies were observed with respect to the airframe side of the cowling door latches. The separated portion of the door was not recovered.

Text from the NTSB. Open the NTSB docket for CEN11CA152 for the full record.