DULUTH, MN, USA
N44VK
CIRRUS VK30
The pilot of N44VK was attempting to verify stall characteristics at the aft center of gravity limit. The pilot of a chase plane and an on board video confirmed that N44VK departed controlled flight. Recovery from the uncontrolled flight was not made prior to impact with the terrain. The airplane came to rest in an upright position with a descent angle measured at 77 degrees. All airframe components recovered were found within 30 feet of the main wreckage. The airplane was not equipped with any antispin or deep stall recovery devices. The investigation revealed flight control continuity. Indications of engine power at impact were evident throughout the engine, propeller, and drive shaft.
HISTORY OF FLIGHT On March 22, 1996, at 1220 central standard time (cst), an Experimental Cirrus VK30, N44VK, piloted by a commercial pilot, was destroyed after a collision with terrain, following an uncontrolled descent. The commercial rated pilot was fatally injured in the accident. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 flight was not operating on a flight plan. The airplane was on a local test flight, attempting to validate stall characteristics with different settings of wing flaps and landing gear. The pilot of the chase airplane, and the on board video camera confirmed that N44VK departed controlled flight before impacting the terrain. FLIGHT RECORDERS A video camera on board N44VK was recording the reactions of yarn tufts attached to the upper surface of the right wing during stalls. The video tape's case and tape were damaged during the accident. On Sunday, March 24, 1996, at the office of Pro Video Productions, Duluth, Minnesota, the original video was repaired. All of the tape was recovered except for approximately one second at the end of the tape. The video tape ends before N44VK impacts with the terrain. A video technician stated that during the maneuver the tape most likely pulled away from the heads of the recorder, causing the recorder to terminate recording. The unedited duplicate of this tape is included as an attachment to this report. WRECKAGE AND IMPACT INFORMATION The airplane came to rest in a upright position on a magnetic heading of 150 degrees. The coordinates obtained from a police global positioning satellite system were north 46 degrees 56.12 minutes, and west 92 degrees 11.91 minutes. Using a police inclinometer the descent angle was measured at 77 degrees. All of the airframe components recovered were found within 30 feet of the main wreckage. The top portion of the right side door was not located, until several weeks after the on scene investigation. The hinge which attached the door to the fuselage was bent, and the gas spring which held the door in the open position was bent with one end missing. The right landing gear was extended and attached to the wing. The left landing gear was separated from the left wing. The gear selector switch was found in the down position. The wing flaps were down at approximately one quarter deflection. All control surfaces and balance weights were found attached. Airspeed indications were 160 knots indicated airspeed on the copilot's side, 136 knots indicated airspeed pilot's side. The pilots seat was bent into a U shape. The horizontal stabilizer was found near the maximum leading edge up position. All three wooden blades of the variable pitch propeller had sustained damage. The drive shaft between the engine's gear box, and the propeller hub showed signs similar to a torsional overload failure. The gear box casting was cracked. Black marks similar in color to the drive shaft dampener were seen on the floor beneath the drive shaft. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was performed on March 23, 1996 at the St. Luke's Hospital, in Duluth, Minnesota. The toxicological testing performed by the Federal Aviation Administration in Oklahoma City, Oklahoma, was negative for all items tested. TESTS AND RESEARCH Before moving the aircraft all engine and airframe controls were checked for continuity. The aileron system was continuous from the chain in the cockpit to both ailerons on the wing. The chain in the cockpit area was broken, and the broken chain link showed evidence similar to an overload failure. Both ailerons could be actuated by pulling on the cables in the cockpit. The on board video showed the right aileron moving during the airplane's descent. The elevator system was continuous from the cockpit to the rod end on the elevator. The elevators could be actuated by using the control cables in the cockpit. The rudder push-pull cables were found still attached to the rudder pedals, and the rudder could be actuated in the cockpit using the push-pull cables. The jack screw which controls the horizontal stabilizer position was found attached, and it operated when a 24 volt battery charger was attached. Both flap jack screws were found attached to their mounts and during the video taping of the stall series, the right flap appeared to operate normally. No evidence of any preexisting rubbing, binding or chaffing was found on any control surface of the aircraft. All engine controls were found attached at the control quadrant in the cockpit, and in the engine compartment. The engine oil and fuel filters were both clean and showed no evidence of contamination. The engine's compressor blades showed evidence of rubbing on the compressor case. The red indicator on the scavage filter case was extended, and the airframe oil scavage pump filter contained numerous pieces of contamination. Two chip detectors from the engine were removed. Both chip detectors were filled with metal chips, and had continuity when checked with a volt-ohm meter. The engine gear box chip detector was removed, and tested positive for continuity when checked with a volt-ohm meter. At this point in the investigation the engine, gear box and engine filters were crated up, and shipped to the engine manufacturers facilities in Indianapolis, Indiana. Investigation of the engine at the manufacturer's facilities on July 8, 1996, revealed no abnormalities with the engine, and indications of power at impact were evident throughout the engine. The engine inspection report is included as a supplement to this report. ADDITIONAL INFORMATION The pilot of N44VK was attempting to verify the stall characteristics of this airplane with the center of gravity at 33 percent mean aerodynamic chord, which was intended to be the aft center of gravity limit for this airplane. The pilot's log book contained an entry for a flight from the previous day for .9 hours, with the center of gravity at 33% mean aerodynamic chord. During the last stall, N44VK was configured with the landing gear down, and the flaps fully extended. A former test pilot who had worked with Cirrus Aircraft was contacted by the IIC on April 8, 1996. The former test pilot recalled three occasions while he was testing the piston engine version of the VK30, where the aircraft departed controlled flight. The former test pilot said that with the flaps extended 40 degrees and the landing gear down the aircraft did not recover as well from stalls when compared with clean configuration stalls. The former test pilot said that the stick force gradient was positive, but very light during all stall tests. The former test pilot said that the original prototype aircraft had differences in the amount of wash-out between the left and right wings, which may have contributed to the departure characteristics. On April 3, 1996, a group of six NASA employees who specialize in high angle of attack and spin research reviewed the video tape showing the departure from controlled flight of N44VK. The group said that when the yarn tufts were indicating air flow toward the leading edge of the right wing, it was a result of a very high angle of attack, and was not uncommon to see during spin research. The group agreed that the aircraft's pitch attitude decreased, during the departure. The airplane was not equipped with any antispin or deep stall recovery devices. Parties to the investigation were the Federal Aviation Administration, Cirrus Design, Allison Engines and the National Aeronautics and Space Administration.
the inadequate handling/performance design capabilities of the airplane which resulted in the inability to recover from an aft center of gravity spin. Factors were the lack of any antispin or deep stall recovery devices, and the aft center of gravity.
Source: NTSB Aviation Accident Database
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