CEN14FA266

The pilot's failure to maintain airplane control during the aerobatic flight, which resulted in the airplane exceeding its critical angle of attack and entering an accelerated stall at a low altitude.

The pilot was performing an aerobatic flight at an airshow event when the accident occurred. The flight team manager witnessed the accident and reported that the airplane entered an intentional inverted flat spin at the apex of an inside loop maneuver. The airplane completed more than 3 rotations in the inverted flat spin before recovering into a dive. The team manager then saw the airplane pitch up and enter an "aggressive" left turn. A review of ground-based video footage confirmed the sequence of events reported by the team manager and showed that, after the pitch up and left roll, the airplane entered a nose-low, descending left spiral that continued to ground impact. The observed flight path was consistent with an accelerated aerodynamic stall after the pilot had recovered from the inverted spin at a low altitude. The airplane cockpit was equipped with an aft-facing video camera that captured the pilot and his flight control movements. A review of the available cockpit footage confirmed that the pilot remained conscious throughout the accident flight and that the ailerons, elevator, and engine had responded to his control inputs. Although the rudder was obstructed from view in the video by the pilot's helmeted head, his observed leg movements were consistent with expected rudder inputs throughout the flight. Further, a postaccident examination of the airplane did not reveal any mechanical anomalies that would have precluded normal operation.

The Stevens Point Municipal Airport, located about 3 miles northeast of Stevens Point, Wisconsin, was served by two asphalt runways, runway 3/21 (6,028 ft by 120 ft) and runway 12/30 (3,635 ft by 75 ft). The airport elevation was 1,110 ft mean sea level. A Garmin GPSMAP 396, serial number 67014609, was recovered from the wreckage and examined at the NTSB Vehicle Recorder Laboratory. The non-volatile data was recovered through a memory-chip recovery process. The final dataset was recorded on May 31, 2014, and was associated with a 0.8-hour flight from Menomonie Municipal Airport (LUM) to STE. The Garmin GPSMAP 396 device did not contain any data associated with the accident flight. A GoPro Hero 3+ digital video camera, serial number 30C3CDE, was recovered from the wreckage and examined at the NTSB Vehicle Recorder Laboratory. A forensic recovery of the memory card revealed eight video files. Seven of the eight video files were not associated with the accident flight. The remaining video file contained 4 minutes 37 seconds of video footage from the accident flight. A review of the available video footage established that the camera was mounted on the glare shield facing aft toward the pilot. The pilot's helmeted head, torso, hips, upper legs, and knees were in the field-of-view. Also visible were the pilot control stick, the inboard portions of both ailerons, the outboard portions of both horizontal stabilizers, and both elevator horns/counterbalances. The vertical stabilizer and rudder were obscured by the pilot's helmeted head. The video camera also recorded audio that detected changes in wind and engine noise during the accident flight. A review of the video footage established that the flight controls were moving in conjunction with the pilot's control inputs and that he closed and locked the canopy before takeoff. The pilot initiated the takeoff by advancing the engine power lever gradually with his left hand. The airplane became airborne in a level attitude while over the runway 21 centerline. About 8 seconds after liftoff, the pilot activated the smoke system with his right thumb on the control stick, and the airplane briefly entered a slight climb before it rolled to the right into an inverted attitude. The inverted airplane was slightly left of the runway 21 centerline. The pilot then pushed the control stick forward to initiate an inverted climb. During the inverted climb, the pilot turned the airplane away from the showline and eventually rolled the airplane upright and continued in a climbing left turn onto a downwind for runway 21. While on the downwind, the pilot made a radio call and activated the airplane's smoke system several times. The airplane continued to climb on the left crosswind and eventually turned upwind for runway 21. At 03:53 (mm:ss) into the recording, the pilot made a radio call, activated the smoke system, and rolled the airplane inverted. After rolling inverted, the airplane continued to fly level briefly before the pilot applied aft control stick with both hands to establish a descending flight path of about 45°. The airplane then completed 2-1/2 right aileron rolls while descending, and smoke was observed trailing the airplane's flight path. By 04:06, the airplane was upright and wings level. The airplane then entered an inside loop maneuver. While the airplane was ascending, the two intersecting runways were visible outside the airplane's canopy. The longitudinal axis of the airplane appeared to be about 20° offset to the runway 3/21 centerline. At 04:17, the pilot reduced engine throttle, and the recorded audio track was consistent with a partial reduction in engine power. About 1 second later, the unrestrained portion of the pilot's shoulder harness straps (strap ends) fell toward the top of the airplane's canopy indicating the airplane had entered a negative-g environment. The pilot applied slight forward control stick with his right hand. By 04:19, the pilot further reduced the engine throttle and applied additional forward control stick input. The airplane's heading remained offset about 20° from the runway 3/21 centerline. The elevator horns/counterbalances showed that the elevator was near maximum deflection as the control stick approached the full forward position. The pilot then applied a left rudder input while holding the control stick in the full forward position. The observed smoke trail was consistent with the airplane yawing. By 04:27, the airplane was established in an inverted spin and had completed one rotation. The pilot was still holding full forward stick with some right aileron input. The airplane completed several rotations while in the inverted spin before the pilot began to move the control stick forward and applied right rudder. The airplane's rotation rate began to slow, and by 04:31, the control stick was being held in a neutral pitch position. The elevator was observed in a neutral position when compared to the horizontal stabilizer. The pilot then moved the control stick to the right, and both ailerons were observed to move in conjunction with the control stick position. The shoulder harness straps were still floating, consistent with the airplane still in a negative-g environment. The pilot was holding the control stick with a clenched right hand. At 04:32, the pilot applied a rapid left aileron and left rudder control input. The ailerons were observed to respond to the control stick movement. The shoulder harness straps were no longer floating, consistent with the airplane in a positive-g environment. The airplane rotation stopped, and there was an increase in engine noise. About a second after the rotation had stopped, the pilot quickly centered the control stick before moving the control stick aft. The elevator was observed to move in conjunction with the control stick movement. The ailerons appeared to be in a neutral position as the airplane pitched up from a nose-low descent toward level flight. Within the next 2 seconds, the horizon became visible behind the airplane. The upright airplane was banked slightly to the right as the airplane neared a level flight attitude. At 04:34, the pilot moved his head to look over his right shoulder. The airplane continued to pitch up and subsequently entered a level climb. The pilot then turned his head back toward the center of the cockpit, his right hand was still firmly griping the control stick, and his left hand was on the engine throttle. Runway 3/21 was observed directly behind the airplane and perpendicular to the airplane's flight path. The airplane then entered an abrupt left roll with a positive pitch angle. The pilot had not commanded the left roll with aileron or rudder control input. The control stick position was consistent with an aft pitch and a neutral roll input. The observed positions of the ailerons and elevator were consistent with the control stick position. The video footage was analyzed frame-by-frame, and the left roll rate appeared to increase rapidly between frames. The pilot was still griping the control stick with his right hand while his left hand remained on the engine throttle. As the left roll developed, the pilot moved the control stick to the right and partially reduced the aft pitch. The airplane continued to roll left, and the runway 30 threshold markings became visible below the airplane. During the left roll, the pilot added additional right roll control and further reduced the aft pitch input. The ailerons and elevator responded to the control stick movement. Throughout the left roll, the pilot was looking forward, and his right hand remained on the control stick and his left hand on the engine throttle. At 04:37, the video footage ended with the airplane still airborne and rolling to the left. The airplane had rolled beyond 90° to the horizon and the runway 30 threshold markings were still visible under the airplane. The final impact sequence was not recorded by the video camer