Air Tractor Inc AT 400 N136DB accident near Levelland, Texas

Probable cause

The in-flight separation of the left aileron's attachment hardware at the connection between the long aileron pushrod and the left aileron bellcrank. Contributing to the accident was maintenance personnel’s improper installation of, or failure to install, the left aileron attachment hardware.

NTSB analysis

The pilot reported that, shortly after takeoff on a postmaintenance test flight, the flight controls felt "stiff." The pilot flew a traffic pattern and intended to conduct a precautionary landing on the runway. However, after the pilot turned the airplane to the final leg in the traffic pattern, the airplane started to roll left. While attempting to level the wings, the pilot observed the left aileron traveling up and down. During the landing, the airplane bounced twice, rolled left, and then cartwheeled.

The airplane had undergone extensive maintenance throughout the year before the accident, and, during this maintenance, maintenance personnel reinstalled the ailerons. The accident flight was the first flight following this maintenance. A postaccident examination of the airplane revealed that the hardware that attached the long aileron pushrod to the aileron bellcrank was not present, and the hardware was not found at the accident site; therefore, it could not be determined whether new or existing hardware was installed during the recent maintenance. However, given that the flight control malfunction occurred immediately following the extensive maintenance, it is likely that maintenance personnel either did not install the attachment hardware at all or did not install it properly, either of which would have resulted in the loss of airplane control and subsequent impact with terrain.

Text from the NTSB. Open the NTSB docket for CEN15LA182 for the full record.