NTSB Identification: FTW95FA394.
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Accident occurred Thursday, September 14, 1995 in HOUSTON, TX
Probable Cause Approval Date: 03/21/1996
Aircraft: MBB BO-105C, registration: N650MS
Injuries: 3 Uninjured.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The pilot reported that during cruise flight at 800 feet MSL, a 'whine' was heard, which was 'slightly' different from the normal whine of the engines. A loud 'snap' or 'bang' was heard followed by severe vibrations. After determining a dual engine failure, the number one engine fire warning light illuminated, and the smell of smoke was noticed. An autorotation was initiated to a mall parking lot. During the autorotation, the pilot increased collective to clear trees bordering the parking lot. The helicopter touched down and slid approximately 200 feet to a stop. When the nurse opened the door to evacuate, smoke billowed into the cabin from the 'tunnel area.' After confirming that the flight crew was well clear, the pilot exited the helicopter. Examination of the helicopter revealed the drive shaft for the left engine had separated from the transmission input shaft flange. Examination of the main transmission lower housing revealed debris partially blocking the oil channel for the left side input pinion. Examination of both engines revealed internal thermal and foreign object damage.

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

the failure of the main transmission's #1 (left) input pinion assembly, due to the partially blocked oil passage which reduced oil flow, resulting in the disconnect of the drive shaft.

Full narrative available

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