NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
Radar data revealed that the introductory instructional flight departed and proceeded toward mountainous terrain adjacent to the intended destination. As the airplane approached the foothills, it entered a series of turns. The radar data did not include altitude information, most likely because the altitude reporting mode of the airplane's transponder was inoperative. A witness, located in her residence near the accident site, observed the airplane flying unusually low along the ridgeline. The airplane then made an abrupt, swooping, and descending turn. As it began to roll out of the turn, the wings started to rock from side to side, and the airplane then immediately descended nose-down into the ground. The airplane did not appear to be trailing smoke or vapor, and the engine was producing a sound consistent with high power throughout the maneuver.
Examination of the wreckage revealed that the airplane struck the ground in a near vertical nose-down attitude. The impact attitude and the witness’s description of the rocking wings followed by an immediate nose-down descent both are consistent with an aerodynamic stall. Analysis of the radar data revealed that, in the final turn, the airplane was flying at a speed of about 77 knots with a turn radius of about 400 feet. To achieve the turn radius observed would have required a bank angle between 50 and 60 degrees with an associated increase in load factor that would have caused the airplane's stall speed to match or exceed its airspeed. The airplane's design was such that uncoordinated flight control input close to stall speed could result in an unrecoverable spin.
Examination of the airplane's structure, the majority of which was consumed by postaccident fire, and the engine, which sustained heavy thermal damage, did not reveal any mechanical malfunctions or failures that would have precluded normal operation.