On October 21, 2000, about 1407 Eastern Daylight Time, a homebuilt Sonerai II, N188P, was substantially damaged during a forced landing at the Manassas Regional/Harry P. Davis Field Airport (HEF), Manassas, Virginia. The certificated private pilot received minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight conducted under 14 CFR Part 91. According to the pilot, he departed the Winchester Regional Airport (OKV), Winchester, Virginia, and was en route to Washington Executive/Hyde Field Airport (W32), Clinton, Maryland. Shortly after departure from OKV, he crossed the Blue Ridge Mountains at 3,300 feet and encountered severe turbulence and heavy winds. The pilot reported the winds were from the northwest and paralleled his route of flight. He stated the turbulence was "the worst he had ever seen." In a period of 1-2 seconds, the airplane was thrown from 4,500 feet to 2,700 feet and back to 3,600 feet. During the turbulence encounter, the VSI indicated a descent of more than 5,000 feet per minute, and the pilot recalled "pulling at least 4 G's." The pilot reported that as he encountered the turbulence, his right knee came in contact with the dashboard and broke the right and left fuel pump switches. He stated that the right fuel pump switch was "totally shattered," and the left fuel pump switch was partially broken in the "ON" position. The pilot reported that during normal operations, the fuel pump switches would light up when the fuel pumps were operational. After he encountered the turbulence, the right switch did not illuminate, and the left switch was lit intermittently. He also observed erratic fuel pressure indications from the fuel pressure gauge. The pilot stated that he declared an emergency with Dulles Approach Control while at 2,400 feet, and was instructed to contact the Manassas Regional Airport control tower. Shortly after he was cleared to land at Manassas, the left fuel pump light extinguished, and the engine lost power. About 1 mile from the end of the runway, the airplane encountered a downdraft, which caused the airplane to descend from 800 to 200 feet. When the pilot realized he would not make the runway, he landed in an open field. The pilot reported that he received a weather briefing prior to the flight and no wind or turbulence advisories were issued. He additionally stated that he had accumulated 1,600 hours of total flight experience. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed the right fuel pump switch was broken and the left fuel pump switch was partially operational. Additionally, the inspector observed about 4 gallons of fuel in the fuel tank. According to the inspector, fuel was provided to the engine through the operation of the right and left fuel pumps. According to weather data provided by the National Weather Service (NWS), no weather advisories were issued for the route of flight concerning turbulence. The surface observation at HEF, at 1355, was: wind calm, visibility 10 statute miles, sky clear below 12,000 feet, temperature 26.0 degrees C, dew point temperature 12 degrees, altimeter 30.16 inches of mercury. Additionally, the Sterling, VA upper air sounding for 1200Z indicated a strong surface based inversion to 2,090 feet, and decreasing temperatures above. Wind speeds were recorded with the inversion at 32 knots from the northwest to west, and decreasing above the inversion. It should be noted that the NWS does not report mountain wave turbulence unless the area covers more than 5,000 square miles.