LAX07LA065

Prior to flight, the pilot checked the weather and also received a weather briefing from a Flight Service Station. The briefing revealed high winds and mountain obscuration along his route of flight. In order to avoid the adverse weather, the pilot departed on a westerly heading and climbed to 12,500 feet rather than his usual altitude of 8,500 feet, on a northwesterly heading across mountainous terrain. Thirty minutes into the flight he encountered strong downdrafts and wind shear on the lee side of the mountains. He applied full power, and initiated a 180-degree turn but was unable to maintain altitude. The airplane descended into a cloud layer, and continued to experience severe turbulence; the airplane subsequently stalled and entered a spin. The pilot recovered from the spin momentarily, before the airplane again stalled and entered a second spin. The airplane then exited the clouds at approximately 500 feet agl. The pilot then force landed the airplane into rising terrain.

History of flight

On December 27, 2006, about 1330 Pacific standard time, a Beech A36, N4598S, collided with terrain after encountering severe turbulence near Lake Hughes, California. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The private pilot sustained serious injuries; the airplane sustained substantial damage. The cross-country personal flight departed General William J. Fox Airfield (WJF), Lancaster, California, about 1300, with a planned destination of Chico Municipal Airport, Chico, California. Visual meteorological conditions prevailed, and a visual flight rules (VFR) flight plan had been filed.

In a written statement, the pilot reported that on the morning of the flight he checked the weather via the computer, and he also called a Flight Service Station for a weather briefing. The briefing revealed high winds and mountain obscuration along the route of flight. During the preflight inspection, the pilot noted dark clouds in the Tehachapi Pass area, and clear skies to the west. He stated that his usual flight path would take him on a northwesterly heading at an altitude of 8,500 feet. To avoid the weather, he decided to depart on a westerly heading, and climb to 12,500 feet mean sea level (msl) over the Lake Hughes area. Once he had attained his cruise altitude, he observed clear skies, and estimated that he was approximately 5,000 feet above the cloud tops. He then encountered "a strong downdraft/windshear of huge proportions." He applied full power, and initiated a 180-degree turn, but was unable to maintain altitude. The airplane descended into the cloud layer. While in the clouds, the pilot experienced heavy turbulence; the airplane stalled, and entered a spin. The pilot recovered from the spin momentarily before the airplane again stalled, and entered a second spin. The airplane then exited the clouds at approximately 500 feet above ground level (agl). The pilot reported he was "boxed in" and unable to escape rising terrain without entering the clouds. The pilot then found an upsloping hill, slowly bled off airspeed, and performed a "pancake" landing.

Meteorological information

The closest official weather observation station was WJF, which was 24 nautical miles east of the accident site. An aviation routine weather report (METAR) for WJF was issued at 1256. It stated: winds from 250 degrees at 27 knots, gusting to 31 knots; visibility 10 miles; light rain; few clouds 3,000 feet, 4,200 feet overcast; temperature 10 degrees Celsius; dew point -1 degree Celsius; altimeter 29.78 inches of mercury.

AIRMETS for mountain obscuration, turbulence and low level wind shear, as well as SIGMETS for occasional severe turbulence below 15,000 feet, were all issued for California, including portions of the airplane's route of flight.

Around the time of the accident, pilot weather reports from Southern California indicated widespread moderate to severe turbulence, at altitudes ranging between 3,000 and 37,000 feet.