On July 6, 2003, at 1235 mountain daylight time, a Mooney, M20J, N37JK, was substantially damaged when it impacted terrain during departure from Lake County Airport, Leadville, Colorado. The airline transport pilot, the sole occupant, was seriously injured. Visual meteorological conditions prevailed, and an instrument rules flight plan had been filed, but had not been activated, for the cross-country flight being conducted under Title 14 CFR Part 91. The flight was originating when the accident occurred, and was en route to Sedona, Arizona. According to the pilot's accident report, he took off and accelerated in ground effect to normal climb speed. When he initiated the climb, airspeed dropped 20 to 25 knots in just a few seconds. The airplane settled back onto, and went off the end, of the runway. The pilot said the wind was from 160 to 200 degrees at 12 knots with gusts to 16 knots. At 1256, the recorded METAR (routine aviation weather report) at Leadville was as follows: Wind variable at 3 knots; visibility, 10 statute miles; few clouds, 11,000 feet; temperature, 21 degrees Celsius; dew point, minus 7 degrees Celsius; altimeter, 30.35 inches of mercury; peak wind, 180 degrees at 35 knots; rain began at 1235, and ended at 1246; sea level pressure, 1009.0 millibars. The computed density altitude was approximately 12,575 feet above mean sea level. According to a Lake County deputy sheriff who examined the accident site, the airplane struck two runway end lights, traveled 40 feet through the air, struck the ground, became airborne for 158 feet, struck the ground, became airborne for 479 feet, struck the ground and went over a steep hillside, struck a barbed wire fence and post, and slid 422 feet before coming to a halt. The empennage separated from the airplane during the accident sequence. Total distance from the runway end to where the airplane came to a halt was about 1,100 feet.