Meadow Lake Airport, CO, USA
N17TD
GLASFLUGEL H201B
The glider flight was being conducted to test the operation of a prototype winch launch system utilizing a computer aided launch control (CALC) hydrostatic system. During the launch, a programming anomaly within CALC limited the maximum winch speed to 32 miles per hour, causing the winch cable to release as the glider climbed away from the ground. The pilot pushed the nose of the glider down, but insufficient altitude was available to recover the glider. The glider impacted the runway in a level attitude, cracking the fuselage.
On May 5, 2009, at 1307 mountain daylight time, a Glasflugel Libelle H201B model glider, N17TD, was substantially damaged during a forced landing following an attempted winch assisted takeoff. The private pilot was seriously injured. The flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 91 without a flight plan. The local flight was departing from Meadow Lake Airport (00V), Colorado Springs, Colorado. Visual meteorological conditions prevailed at the time of the accident. The flight was being conducted to test the operation of a prototype Hydrowinch, LLC Club Series winch launch system. The pilot stated that during the launch the glider suddenly stopped accelerating and the tow cable disconnected. Video of the accident sequence showed the glider becoming airborne in approximately 30 feet and reaching a maximum height of about 20 feet. The tow cable parachute, which inflates after release from the glider, was seen to inflate as the glider started to become airborne. The glider then nosed over, changed to a level attitude, and impacted the runway. Examination of the glider revealed the fuselage cracked aft of the cockpit. The winch was powered by a diesel engine connected to a computer controlled hydrostatic drive system. The hydrostatic drive system was controlled by a computer aided launch control (CALC) system. CALC was designed to adjust winch acceleration and maximum speed produced through the hydrostatic system based on glider type and weight. In the case of the Glasflugel Libelle H201B, acceleration force should have been limited to about 50 percent of system capability and a desired speed of 65 miles per hour. A review of the computer data for the accident launch showed the computer limited maximum speed to 50 percent, or 32 miles per hour, as opposed to the acceleration force. The winch had conducted seven successful launches in 2008 before suffering a mechanical break down and subsequently having a new computer installed. The accident flight was the second flight operation for the repaired unit. The first attempted flight operation after repair resulted in an aborted takeoff due to a non-CALC related, winch operator error.
A programming anomaly within the winch's computer aided launch control system, which incorrectly limited the maximum winch speed during launch of the glider.
Source: NTSB Aviation Accident Database
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