Accident Sequence
Television news crews filming general aviation operations at an airport captured a takeoff accident on video. The footage begins with the airplane on its takeoff roll, accelerating for nearly two-thirds of the runway before becoming airborne. After liftoff, the airplane climbed to approximately 40 feet, at which point the wings began to wobble. The airplane then settled back to the ground into rising terrain off the end of the runway, slid along the ground, and abruptly flipped onto its back.
Environmental Conditions
The windsock at the approach end of the runway appeared limp, indicating little to no wind. The outside air temperature was 96°F, and the field elevation was 1,286 feet msl, resulting in a density altitude of 4,125 feet. The highest terrain elevation directly ahead of the airplane was 1,350 feet msl, approximately 4,860 feet from the start of the takeoff roll. The elevation difference between the point the airplane left the runway and the elevated terrain ahead was 80 feet. Video analysis showed that immediately after liftoff, the airplane crabbed to the left about 7 degrees while remaining over the runway centerline, indicating a sudden transition from calm wind to a left crosswind early in the climb. The video also depicted a left crosswind at the departure end, with trees in the background waving in what appeared to be a moderate breeze. No determination could be made whether the crosswind had a tailwind or headwind component.
Aircraft Information
The airplane was equipped with an engine turbonormalizing system. A supplemental type certificate (STC) for this system allowed an increase in gross weight to 4,000 pounds when operated in the normal category. The airplane's weight at takeoff was 4,095 pounds. The aircraft was also instrumented with a JPI EDM-800 Engine Analyzer, which recorded consistent engine operation throughout the takeoff and climb at a power level between 91 and 94 percent.
Performance Analysis
A video study concluded that the airplane's ground speed was 80 ± 4 knots as it crossed the end of the runway, consistent with the Pilot's Operating Handbook (POH) recommended climb speed. Based on the STC documentation, the calculated takeoff distance to clear a 50-foot obstacle was 4,030 feet. An independent computer model simulating the airplane's performance at a weight of 4,100 pounds and a density altitude of 4,100 feet msl resulted in a climb rate of 911 feet per minute and predicted that the airplane would clear the terrain ahead by 148 feet.
Pilot Report and Probable Cause
The pilot reported feeling a gust of wind from the left shortly after takeoff. Based on the evidence, it is likely that the airplane encountered a sudden wind from the left during the initial climb, which degraded the airplane's climb performance and led to a stall/mush condition.