NTSB Final: Trike Fatality Caused by Tumble
On March 13, 2010, a ski-equipped Antares trike impacted terrain about two miles north of the Birchwood Airport in Chugiak, Alaska. The aircraft was substantially damaged, and the experienced 54-year-old private pilot was fatally injured. There were no witnesses, and initially the cause of the accident eluded investigators. There was evidence of in-flight airframe failure. The pilot was found about 10 feet from the wreckage, but there were no tracks in the snow and the automotive-style seatbelt had apparently failed. Some weeks later a digital video camera that had been mounted on the trike was found at the site after a snow melt, and investigators learned the camera had captured the tragic crash.
The pilot was said to be highly experienced in hang gliders and in paragliders, holding numerous state records. He had flown trikes for about 10 years. The video revealed the craft had flown well outside the normal operating envelope and entered a “tumble mode” which is known to be possible in hang gliders and trikes but is seldom witnessed. Investigators were suspicious that this might have been the case because the wing breakage was almost identical to a prior UK tumble accident report. All of the upper and lower flying wires were intact and still attached. But the trike control bar was broken, and the internal backup safety cable was severed.
The video revealed the trike had been flying at a low altitude over the snow-covered flats when it entered a steep climbing right turn that continued to nearly 90 degrees. The climb appeared to stop at which point the nose fell through the horizon rapidly. A frame-by-frame analysis of the video confirmed the in-flight breakup characteristic of the tumble mode which is said to be capable of reaching a rotation rate of 400 degrees per second in the longitudinal axis.
During the tumble, the camera mount broke and the camera departed the aircraft, but it continued to record as it fell alongside. The camera attained a position below the aircraft and showed the pilot separate from the aircraft above the treetops or about 80 feet from the impact surface. The tumble mode can be triggered in weight-shift trikes and hang gliders when the wing stalls at extreme bank angles or extremely high pitch attitudes, or when the pilot attempts aerobatic maneuvers. You can see an example of a trike tumble here. For more details about the accident, read the National Transportation Safety Board report.