NTSB Identification: FTW96LA050.
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Accident occurred Tuesday, November 21, 1995 in ESTANCIA, NM
Probable Cause Approval Date: 06/22/1996
Aircraft: Beech M35, registration: N9886R
Injuries: 2 Minor,1 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.

While cruising at 9,500 feet MSL, the pilot noticed 'vibrations' accompanied by a 'slight' loss of power. He then 'heard a loud noise,' observed smoke, and the engine lost 'all power.' Subsequently, the airplane collided with trees during a forced landing on wooded/mountainous terrain. Engine examination revealed the following: A hole, 3 inches in diameter, was found adjacent to the #1 cylinder's attachment point on the right side of the crankcase. Debris from the #1 and #2 pistons and the #1 and #2 connecting rods was found throughout the interior of the crankcase. According to an FAA inspector's report, 'Cylinders 1 and 2 evidenced a catastrophic failure similar to that caused by detonation from uneven fuel distribution.' The rear crankcase journals were dry and displayed thermal damage. The interior of the crankcase and rear section of the crankshaft displayed impact damage associated with internal engine component failures. Part of an air intake bypass door from the throttle body air intake was found lodged in the intake port of the #6 cylinder. Examination of the throttle body revealed that a replacement air intake door had been installed, but maintenance records did not reveal service performed on (or a replacement of) the bypass door.

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

improper maintenance and inspection of the engine, ingestion of an air intake bypass door into the engine intake, detonation (or preignition), and failure of the #1 and #2 piston and connecting rod assemblies. A factor relating to the accident was: the lack of suitable terrain for a forced landing.

Full narrative available

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