Piper PA-23-250 N6521Y accident near Hemet, California

Probable cause

Maintenance personnel’s failure to properly inspect and replace damaged aileron control cables, which resulted in fatigue separation of the aileron control cable and loss of control of the aircraft.

NTSB analysis

The accident pilot and a second company pilot were flying in the same general area to photograph parcels of land. As the pilots were beginning their photography passes, the company pilot heard the accident pilot make distress calls on the radio. The accident pilot did not respond when asked to clarify the radio calls.

ADS-B data revealed the airplane approached the area to be photographed from the west, made a turn north to enter the area, then made a turn back to the southwest. The airplane then started a right descending turn about the time it intercepted its inbound course to the area. The last data captured the airplane, about 1,000 ft above the ground, about 177 knots groundspeed, in a 2,000 ft-per-minute descent, and about 950 ft northwest of the accident site. The camera system mounted in the airplane recorded the airplane, at that time, in a 31° nose-down attitude, and a 79° right roll.

The airplane struck steep mountainous terrain at a high speed, and the fuselage sustained substantial damage throughout. The wings, the vertical stabilizer, and the right side of the stabilator separated from the airplane.

Examination of the aileron control by the NTSB materials laboratory revealed that a cable had broken under fatigue in a location near the aileron control bellcrank, likely resulting in a loss of control of the airplane. The airplane was maintained in accordance with the operator’s annual maintenance schedule; however, postaccident examination of the aileron control cable revealed that in addition to the fatigue break, multiple individual broken wires were discovered protruding from the strands, which would have required replacement of the cable upon discovery during required checks of the cable.

The toxicology report for the pilot identified positive results for a cannabis metabolite; however, amounts discovered were unlikely to have been impairing. Given the circumstances of the accident, it is unlikely that the pilot’s use of cannabis contributed to the accident and that the pilot lost control of the airplane due to the fatigue failure of the aileron cable.

Text from the NTSB. Open the NTSB docket for WPR20LA135 for the full record.