NTSB Identification: LAX92LA360.
The docket is stored on NTSB microfiche number 47598.
Accident occurred Saturday, August 22, 1992 in BIG BEAR, CA
Probable Cause Approval Date: 09/14/1993
Aircraft: SOCATA TB-10, registration: N20BN
Injuries: 4 Minor.

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

IN HIS WRITTEN STATEMENT THE PILOT SAID THAT AFTER DEPARTURE ON RUNWAY 25 HE TURNED IN A SOUTHWEST DIRECTION TO CROSS A RIDGE LINE AT AN ALTITUDE OF ABOUT 7,900 FEET MSL. HE SAID THAT NEAR THE RIDGE LINE THEY ENCOUNTERED A SUDDEN DOWN DRAFT AND HE COULD NOT ARREST THE DESCENT PRIOR TO COLLIDING WITH TREES. AN EYE WITNESS TO THE CRASH SAID THE AIRCRAFT NEVER ACHIEVED MORE THAN ABOUT 300 FEET AGL AT ANY TIME AFTER TAKEOFF. THE WITNESS OBSERVED THE AIRCRAFT IN A NOSE HIGH ATTITUDE BEGIN A RIGHT TURN, THEN IT DESCENDED BELOW THE TOPS OF SOME TREES AND OUT OF VIEW. TWO OTHER WITNESSES REPORTED HEARING THE SOUNDS OF A LOUD AND STRONG ENGINE UNTIL THE SOUNDS OF TREE IMPACTS WERE HEARD. THE AIRPORT IS IN A MOUNTAIN VALLEY AT AN ELEVATION OF 6,750 FEET. MOUNTAIN RIDGES AND PEAKS RISE AN AVERAGE OF 2,000 FEET ABOVE THE VALLEY FLOOR ON ALL SIDES OF THE AIRPORT. THE AIRPORT IS AT THE EAST END OF THE VALLEY AND A LARGE LAKE. A DAM IS AT THE WEST END OF THE VALLEY AT A 'V' NOTCH IN THE SURROUNDING MOUNTAINS. WEST OF THE DAM THE TERRAIN DROPS OFF RAPIDLY TO THE GREATER LOS ANGELES BASIN. THE DENSITY ALTITUDE WAS CALCULATED TO BE ABOUT 9,400 FEET. OTHER PILOTS WHO DEPARTED FROM THE AIRPORT REPORTED THAT TURBULENCE EXISTED OVER THE VALLEY NEAR THE SURROUNDING RIDGES.

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

THE PILOTS DECISION TO ATTEMPT CROSSING A RIDGE LINE AT AN ALTITUDE INSUFFICIENT TO ALLOW FOR CONTINGENCY ACTIONS IN THE EVENT OF AN ENCOUNTER WITH DOWN DRAFTS OR TURBULENCE. FACTORS IN THE ACCIDENT WERE THE HIGH DENSITY ALTITUDE AND THE FLIGHT'S ENCOUNTER WITH A DOWN DRAFT.

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