NTSB Identification: LAX96FA096.
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Accident occurred Friday, January 19, 1996 in CEDARVILLE, CA
Probable Cause Approval Date: 12/16/1996
Aircraft: Beech 55, registration: N4088A
Injuries: 2 Fatal.

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 was operating on a VFR on top IFR clearance when he inadvertently encountered a mountain wave condition while flying in a dark moonless night. The radar data showed that the airplane began a 612 FPM descent for 1,000 feet and then abruptly climbed 300 feet before the airplane's transponder code disappeared from the sector controllers radar screen. The pilot did not make any radio transmissions during the accident sequence of events. The airplane crashed in a vertical nose-down attitude into a lake and was buried about 20 feet in the muddy silt terrain. The wreckage examination disclosed no evidence of an in-flight breakup or any preexisting airplane malfunctions or failures.

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

the pilot's poor preflight planning by not obtaining a weather briefing and his inadvertent encounter with a mountain wave condition. The moonless dark night was a factor in this accident.

Full narrative available

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