NTSB Identification: CHI90LA074.
The docket is stored on NTSB microfiche number 40656.
Accident occurred Tuesday, January 30, 1990 in JANESVILLE, WI
Probable Cause Approval Date: 12/30/1992
Aircraft: MBB BK-117A-1, registration: N117M
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

THE PILOT STATED THAT HE AND A COMPANY MECHANIC WERE IN CRUISE FLIGHT AT 2,000 FEET MSL ON A MAINTENANCE FLIGHT TEST, WHEN HE HEARD A NOISE, 'OBSERVED DEBRIS IN ALL DIRECTIONS FROM THE MAIN ROTOR...(AND) SEVERE VIBRATION WAS EXPERIENCED.' THE PILOT MADE AN EMERGENCY LANDING IN A SNOW-COVERED FIELD. POST-ACCIDENT EXAMINATION REVEALED THAT THE ENGINE COWLING ON THE LEFT SIDE OF THE AIRCRAFT HAD SEPARATED WHILE IN FLIGHT, CONTACTING AND DAMAGING THE MAIN ROTOR BLADES. SEVERAL PIECES OF THE SEPERATED COWLING WERE RECOVERED AND INSPECTED. THE LATCHES SHOWED NO MALFORMATION/STRETCHING, AND APPEARED TO BE CAPABLE OF NORMAL OPERATION.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

THE PILOT-IN-COMMAND FAILED TO ENSURE THAT THE ENGINE COWLING LATCHES WERE PROPERLY SECURED PRIOR TO DEPARTING ON THE MAINTENANCE TEST FLIGHT; THE COWLING CAME LOOSE DURING FLIGHT, AND CONTACTED THE MAIN ROTOR BLADES BEFORE IT SEPARATED FROM THE HELICOPTER.

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