Air Tractor Inc AT-502 N198LA accident near Forrest City, Arkansas

Probable cause

The in-flight separation of the left aileron's push-pull rod and hardware. Contributing to the accident was the failure of maintenance personnel to apply proper torque to the self-locking nuts.

NTSB analysis

After making an agricultural application, the pilot made a climbing left turn; the airplane then began vibrating and shaking. The pilot was able to return the airplane to level flight, but it rocked left and right, with the left aileron going up and down from stop to stop. The pilot chose to perform an emergency landing in a field next to an airport. A postaccident examination of the airplane revealed that the two aileron push-pull rod bolts were missing. The bolts and associated hardware were not located among the wreckage. The airplane had undergone extensive maintenance about 5 months before the accident. A review of the airplane's maintenance manual revealed that the nuts installed in the airplane control system are self-locking nuts, which can loosen if insufficient torque is applied to them. It is likely that maintenance personnel applied improper torque to the aileron's push-pull rod self-locking nuts, which resulted in the eventual loosening of the nuts and the separation of the left aileron's push-pull rod and hardware.

Text from the NTSB. Open the NTSB docket for CEN13LA168 for the full record.