Piper PA 28-180 N4871L accident near Santa Rosa Valley, California

Probable cause

The pilot's exceedance of the airplane's critical angle of attack while intentionally maneuvering in a steep bank at low altitude, which resulted in an accelerated aerodynamic stall and subsequent loss of control.

NTSB analysis

The commercial pilot and his son were conducting a personal flight. About 15 minutes after takeoff, the airplane flew a series of passes over a horse arena where the pilot's daughter was riding. The arena was situated within a geographic bowl depression, surrounded by hilly terrain and adjacent to three sets of power transmission lines. A pilot witness in an airplane flying above the accident airplane described the accident airplane's flight path as low and erratic, and a witness close to the arena described the initial pass as "aggressive." The pilot conducted the final pass over the arena at a much lower altitude than the previous passes. Multiple witnesses described the engine noise as "sputtering" and then going quiet either during the descent for the final pass, or just as the airplane flew over the arena. The engine sound then increased as the airplane climbed and entered a steep right bank, then descended into power lines and impacted the ground about 600 ft south of the arena. Calculations based on witness reports and impact geometry indicated that the radius of the turn before impact would have required a high angle of bank, resulting in an increase in stall speed, which would have led to an accelerated stall at an altitude too low for recovery.

Examination revealed no anomalies with the airframe or engine that would have precluded normal operation, and damage signatures and witness accounts indicated that the engine was producing power at the time of the accident. Damage to the airplane's fuel tanks indicated that they contained fuel at the time of impact.

The pilot's son, who was not a pilot, was seated in the front left seat. Since the airplane was equipped with dual controls, it could not be determined who was flying the airplane at the time of the accident.

The pilot was familiar with the terrain in the area of the accident site. Witnesses stated that he had performed low passes there multiple times in the past and was aware of the power lines at the edge of the arena. The reduction in engine noise as reported by witnesses could have been the result of an actual loss of engine power or a power reduction made by the pilot to descend more rapidly in order to perform the pass at a lower altitude; however, if the pilot had been flying at an appropriate and safe altitude and the airplane had experienced a loss of engine power, it would have been within gliding distance of open terrain adequate for a forced landing. Given the pilot's previous behavior and the circumstances of the accident flight, it is likely that the pilot was performing an intentional, ostentatious display at low altitude when the accident occurred.

Toxicology testing of the pilot indicated the presence of multiple impairing medications, as well as tetrahydrocannabinol carboxylic acid, a metabolite of tetrahydrocannabinol (THC), the active compound in marijuana. However, no blood was available for toxicology testing, and there is no known relationship between tissue levels and impairment. As a result, whether the pilot's use of multiple potentially impairing substances contributed to the accident could not be determined.

Text from the NTSB. Open the NTSB docket for WPR17FA120 for the full record.