Starkville, MS, USA
N401MS
Windward OWL
The commercial pilot lost control of the experimental glider during a test flight, following the in-flight separation of both wings. The pilot was ejected from the disabled glider and was able to deploy his emergency parachute for a safe landing. The operator reported that the glider was towed to a pressure altitude of 12,000-feet by a Cessna tow-plane. During the test flight sequence, the aircraft experienced an in-flight break-up when both wings separated from the fuselage while maneuvering at 7,675 feet. Prior tests on the glider indicated the wing flutter speed was approximately 169 knots. The experimental glider was also equipped with an on-board flight data recording system that sent data to a ground station during the test flight. Post flight analysis of the data indicated that during the nose down attitude, the wings separated from the airframe at approximately 162 knots. The flight engineer stated that the glider was equipped with an airspeed indicator that indicated a maximum airspeed of 105 knots. The stop-point for the airspeed indicator was just beyond the maximum indicated airspeed. The pilot was unaware that the "never exceed" speed of 123 knots had been breached during the descent. The glider was reported to have been equipped with a ballistic recovery system (BRS) parachute, which was successfully deployed. The fuselage of the glider came to rest approximately 2.5 miles northeast of the airport.
On October 18, 2006, at 1509 central daylight time, a Windward Performance OWL experimental glider, N401MS, was substantially damaged upon impact with the ground following an in-flight breakup while maneuvering near Starkville, Mississippi. The commercial pilot, sole occupant of the glider, sustained minor injuries after abandoning the glider and deploying his emergency parachute. Visual meteorological conditions prevailed for the test flight. A company visual flight rules (VFR) flight plan was filed for the 14 code of Federal Regulations Part 91 flight. The local flight originated from the Starkville Airport at 1444. The glider, serial number 001, was owned and operated by Mississippi State University Raspet Flight Research Laboratory for flight testing purposes. The flight test research is part of a contract to develop a long term unmanned aerial vehicle (UAV) from a carbon fiber designed referred to as Ultralight Sensor Platform (ULSP). The ultralight glider was registered in June 2006 and had a gross weight of approximately 484 pounds. The glider had accumulated a total of 3 hours flight time, prior to the accident flight. The test pilot held a commercial certificate and was reported to have accumulated a total of 8,696 total flight hours, with 2,156 hours in gliders and 3 hours in the same make and model glider. The operator reported that a preflight briefing for the test flight was held the day before the accident, and an abbreviated briefing was held on the morning of 18 October 2006. The glider departed from Starkville Airport (KSTF) at approximately 1444 hours, being towed to altitude by a Cessna 188 airplane and was chased by the laboratory's Hughes 369A/OH-6A helicopter. The maneuvers for the test flight took place approximately 5 nautical miles north of KSTF at an altitude of 12,000 feet and below. According to the operator, after being released from the tow airplane, the flight proceeded normally through event number 18 prescribed by the flight test cards. Event 19 called for a 2/3 left aileron deflection "up" at 80 knots indicated airspeed. During performing event number 19, the pilot attempted to roll the aircraft left and maintain a 2/3 aileron deflection. As the pilot rolled to the left, the glider began to nose down and rapidly increase in airspeed. The pilot elected to continue to roll the airplane until it the wings were level in the inverted position. As the airplane leveled out, the indicated airspeed reached 105 knots. The pilot then began increasing the back pressure on the yoke in order to recover to straight and level flight. While recovering, the pilot heard what he termed "a loud explosion." The pilot reported on the Pilot Aircraft Accident Report ( NTSB Form 6120.1/2) that the wings separated from the aircraft during the rapid descent. This was confirmed by the chase pilot and other eye-witnesses aboard the chase helicopter. The glider was reported to have been equipped with a Ballistic Recovery System that was installed in the aft portion of the fuselage. The operator added that during the in-flight break up, the interior wing spar connecting the two central wing sections collapsed. A connecting line from the Ballistic Recovery System to a control lever in the cockpit was engaged when the wing spar broke. The abrupt loss of velocity from the Ballistic Recovery system slowed the fuselage while ejecting the pilot and part of the cockpit along the flight path. The test pilot reported that he deployed his emergency parachute shortly after being ejected from the glider. The fuselage of the glider was able to descend to the ground under the recovery parachute and sustained minor damage. The right wing of the glider also sustained minor damage and contained a large section of the central wing spar. The left wing sustained substantial damage as the wing root was a primary fracture point of the breakup. Prior tests on the glider indicated the wing flutter speed was approximately 169 knots. The experimental glider was also equipped with an on-board flight data recording system that sent data to a ground station during the test flight. Post flight analysis of the data indicated that during the nose down attitude, the wings separated from the airframe at approximately 162 knots. The flight engineer stated that the glider was equipped with an airspeed indicator that indicated a maximum airspeed of 105 knots. The stop-point for the airspeed indicator was just beyond the maximum indicated airspeed. The pilot was unaware that the "never exceed" speed of 123 knots had been breached during the descent. Weather reported at Golden Triangle Municipal Airport (KGTR),located approximately 13 miles northeast of the accident site, at 1555 central daylight time was reporting clear skies, 10 miles visibility, and no ceiling. Wind were from the southeast at 5 knots with no gusts, and the temperature was 86 degrees Fahrenheit.
The structural failure of the airframe due to the inadvertent excessive airspeed during maneuvering.
Source: NTSB Aviation Accident Database
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