SUNDANCE, WY, USA
N3021
AS+ Ltd AC-4B
A glider launch was being conducted, using a vehicle tow and a mechanical advantage/pulley arrangement. During the launch, the tow rope became snagged on vegetation (alfalfa crop stuble), then slack developed in the tow rope as the rope came loose from the stuble. When slack was taken up, it 'jerked' the glider, which pitched up. The pilot released the tow rope, but the glider settled (stall) and rolled approximately 25 degrees left wing down. The wing contacted the ground, and the glider spun around and came to rest facing backwards. This resulted in substantial damage to the wings and fuselage.
On September 14, 1997, at 1745 mountain daylight time, an AS + LTD model AC-4 glider, N3021, settled after an auto launch, struck one wing tip on the ground, and crashed on the Canfield Ranch, 10 miles southwest of Sundance, Wyoming. The certified flight instructor pilot was not injured and the glider sustained substantial damage. Visual meteorological conditions existed and no flight plan was filed for this personal flight conducted under Title 14 CFR Part 91. The flight was originating at the time of the accident. According to the attached pilot statement and a telephone interview with the pilot, this was the fourth flight of the day, all of which used a vehicle tow pulley system for launch. The mechanical advantage of this system was 3 to 1, the same as used on the third launch and the wind was a right quartering head wind estimated to be 5 to 7 knots. The pilot said that during the tow, the rope became entangled in some alfalfa stubble. When it came loose from the stubble some slack occurred. When the slack was taken up it caused the tow rope to "jerk" the glider, which then pitched up. Altitude at the time was about one wing span, according to the pilot, and about 800 feet into the takeoff run. The pilot said he released the tow and attempted to set up for a landing; however, the left wing dropped and the glider struck the ground with the left wing in about a 25 degree left wing down attitude. The glider reversed heading and came to rest approximately 900 feet from where the takeoff had started. (See attached narrative and drawing). Substantial damage was done to the fuselage and both wings.
improper planning/decision by the pilot, which led to a snag and sudden slack in the tow rope, and necessitated an aborted launch (emergency landing) after initial liftoff. This in turn led to an inadvertent stall, a wing drop, and the left wing tip dragging the ground. A factor relating to the accident was: the restricted movement of the tow rope after it became snagged on the crop stubble.
Source: NTSB Aviation Accident Database
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