WPR09LA463 · Frazier Tangent

The pilot was performing high speed taxi tests in an experimental category airplane that he had designed and built. The airplane was configured with a T-tail, a canard wing forward of the cockpit with elevator control surfaces, and had two 28-hp engines mounted facing aft along the trailing edge of the wings in a pusher type design. The main landing gear were located forward of the engine nacelles. To address a lack of pitch response experienced during previous tests, the pilot had increased the size of the canard control surfaces, and moved the center of gravity further aft. During the first taxi run the electronic flight information system (EFIS) recorded a maximum pitch of 9 degrees, and maximum airspeed of 67 knots. During the test run that precipitated the accident, the airplane became airborne at the end of the taxi run and rose to about 122 feet above ground level (agl), entered a right-hand turn, stalled, and impacted terrain in a flat attitude. Audible engine sounds could be heard from the airplane throughout the event and the recorded data supported normal engine operation. The last 16 seconds of data recovered from the EFIS corroborated the witness reports, recording the airplane pitching up suddenly from 8 degrees to 45 degrees, the airspeed decaying from 55 to 22 knots, and then entering a rapid vertical descent. A colleague of the pilot stated that in this pusher configured airplane where the propellers are located aft of the main landing gear, a sudden reduction in thrust could cause a pitch up rotation moment around the main landing gear when on the ground. Toxicology testing was consistent with the recent use by the pilot of a medication containing diphenhydramine, an over-the-counter sedating antihistamine that commonly results in impairment; however, the investigation was unable to conclusively determine whether the use of this medication contributed to the accident.

Verbatim NTSB analysis and probable cause from the NTSB dataset