CEN09LA523 · From Here TO There PDQ Inc RV-8

Witnesses reported seeing the airplane perform a maneuver similar to a hammerhead stall. The airplane recovered and then entered a second similar maneuver. One witness reported that during that second maneuver, as the airplane began to descend, the engine made a popping noise and sounded like it lost power. The witness said that the airplane was doing a “twirling effect” until it impacted the terrain. Another witness said that he saw the airplane climbing until it was “almost standing still, then it cut left” and entered a 45-degree nose-down spin. He reported that after the first or second spin he heard the engine “cut out then backfire about 3 times and then it sounded like it quit.” The witness stated that the airplane kept spinning until it was near the ground, at which time it appeared to “straighten out.” He stated the airplane then disappeared behind a hill and, a second later, he heard the impact. The engine monitoring system recorded data throughout the flight. The data indicated that the engine rpm and manifold pressure fluctuated at different times throughout the flight. The engine rpm increased from a low of 518 rpm to 1,896 rpm then back down to 1,554 rpm in the last 5 seconds of recorded data. During the same time, the manifold pressure increased from 16.3 inches up to 22.5 inches then down to 7.3 inches at the last recorded data. A postaccident inspection of the engine did not reveal any preexisting failures or malfunctions that would have resulted in a loss of engine power.

Verbatim NTSB analysis and probable cause from the NTSB dataset