Serious incident Beechcraft B200 Super King Air N770M, Monday 22 July 1991

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Date:	Monday 22 July 1991
Time:	09:05 LT
Type:	Beechcraft B200 Super King Air
Owner/operator:	Marshall & Isley Bank
Registration:	N770M
MSN:	BB1330
Engine model:	P&W PT6A-42
Fatalities:	Fatalities: 0 / Occupants: 8
Other fatalities:	0
Aircraft damage:	Minor
Category:	Serious incident
Location:	Greenbay, WI - United States of America
Phase:	En route
Nature:	Executive
Departure airport:	Milwaukee, WI (KMKE)
Destination airport:	Greenbay, WI (KGRB)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
THE TWIN-ENGINE TURBO PROP AIRPLANE WAS CRUISING AT 8000' MSL, WHEN THE LEFT ENGINE'S OUTBOARD AFT UPPER ACCESSORY CASE COWL DOOR SEPARTED FROM ITS MOUNT. THE COWL DOOR STRUCK THE TOP SURFACE OF THE LEFT WING (OUTBOARD OF THE ENGINE NACELLE) & PENETRATED THE WING'S FUEL CELL. THIS RESULTED IN FUEL SIPHONING & PROMPTED THE PILOT TO PERFORM A PRECAUTIONARY ENGINE SHUTDOWN. THE AIRPLANE WAS LANDED WITHOUT FURTHER INCIDENT. AIRWORTHINESS DIRECTIVE (AD) 91-18-11 (EFFECTIVE 9/3/91) REQUIRED STRUCTURAL MODIFICATION OF THE AFT UPPER COWL ASSEMBLY DOORS TO PREVENT INFLIGHT SEPARATION.

Probable Cause: INADEQUATE AIRFRAME DESIGN, WHICH RESULTED IN THE IN-FLIGHT SEPARATION OF THE LEFT ENGINE'S OUTBOARD AFT UPPER COWL DOOR.

Accident investigation: