NTSB Identification: LAX04FA271.
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Accident occurred Saturday, July 17, 2004 in Bishop, CA
Probable Cause Approval Date: 10/27/2005
Aircraft: Beech 58, registration: N807Q
Injuries: 3 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 airplane impacted a glacier at 12,270 feet mean sea level (msl) after the pilot attempted to reverse course out of a bowl-shaped valley in the Sierra Nevada mountain range. Ground scar analysis and crush angle measurements on the airplane disclosed that it descended in a near vertical nose down attitude to impact on the glacier. The valley was surrounded by higher peaks and ridges, and the accident site was about 1.3 nautical miles southeast of the direct point-to-point course between the departure and destination airports. At the northeast end of the valley, an opening led down slope through lower mountains and valleys to the airplane's departure point. Satellite imagery indicated that a low layer of stratiform clouds was present over the mountains during the time period following the airplane's departure. The accident site was under the northern edge of these low clouds. Based on the cloud radiative temperatures observed on the satellite imagery, the cloud tops were 16,000 feet mean sea level and the cloud bases were between 10,000 and 14,000 feet msl. The bowl-shaped valley was about 2,450 feet in diameter near the tops of the higher peaks and about 1,200 feet at the elevation of the wreckage. The bank angle required for a turn radius of 1,225 feet at an airspeed of 104 knots (best rate of climb) is 40 degrees. At 156 knots (maneuvering airspeed), the airplane's bank angle would have been 65 degrees. Using a radius of 637.5 feet (the accident site elevation diameter) and 104 knots, the bank angle would have had to have been at least 60 degrees to complete the turn. At 156 knots, the required bank angle would have been about 75 degrees. According to stall speed versus angle of bank data for the airplane, the stall speed would be 85 knots at 40 degrees of bank varying to 105 knots indicated air speed at 60 degrees of bank. No evidence of mechanical malfunction or failure was found during a post accident examination of the airplane and engines. Internal signatures in the propeller hubs disclosed that both engines were producing power symmetrically at the time of impact.

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

the pilot's continued VFR flight into marginal weather conditions with lowering ceilings in a box canyon in mountainous terrain, and his subsequent inability to maintain an adequate airspeed while maneuvering to reverse direction, which led to an accelerated stall and spin.

Full narrative available

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