CHI07LA104 · Piper PA-22-108

The passenger reported that during cruise flight the airplane inexplicably began a shallow left turn that the pilot was unable to counteract. The pilot reportedly moved the yoke to the left and right without any effect on the left bank angle. The airplane continued the unintended left turn with an increasingly steeper bank angle for three complete turns. The passenger reported that the airplane's pitch was vertically nose-down at the completion of the third turn, at which time the airplane impacted trees and terrain. The aileron control cable circuit was examined during the investigation. The inboard end of the right aileron upper cable was missing its eye splice and thimble. The cable had an approximate 90 degree bend at the location corresponding to the eye, consistent with residual deformation associated with an eye loop. The cable separation did not exhibit any kinking or heavy rubbing. The remaining sleeve (nicropress) on the right aileron upper cable did not conform to the manufacturer's specified crimp dimensions and had tooling markings that were not consistent with the use of the specified installation tool. In a properly installed eye splice, the cable should fracture before pulling out of its corresponding sleeve. The aileron cables used had a specified limit load of 2,000 pounds. The remaining eye splice on the right aileron upper cable pulled out of its sleeve at 476 pounds. The other five eye splices tested held more than 1,600 pounds before failure occurred in the cable. A review of the aircraft's maintenance logbooks did not reveal any specific mention of aileron control cable replacement. However, given the variability in the appearance and characteristics of the other aileron cable sleeves, it is likely that the nonconforming sleeves were not of original manufacture.

Verbatim NTSB analysis and probable cause from the NTSB dataset