Aviat Aircraft Inc A 1B N299CA accident near Prairie Du Chien, Wisconsin

Probable cause

The fatigue failure of the aileron hinge bracket tubing for reasons that could not be determined based on the available evidence.

NTSB analysis

Following the aerial photography portion of the flight, the commercial pilot climbed the airplane to 3,500 ft mean sea level and proceeded toward the destination. About 5 minutes later, he felt "light buffeting" as the airplane rolled left. He attempted to counteract the left roll by applying right control stick pressure, but the airplane continued to roll left. He input right rudder to stop the left roll and decided to return to the airport of origin, 10 nautical miles away. He used the rudder to maneuver the airplane and landed uneventfully. After parking the airplane, he moved the control stick left and right several times and the outboard end of the left aileron fell to the ground.

Review of airplane maintenance records revealed that, about 9 years before the accident, the left wing tip was replaced due to "hangar rash," though there was no specific mention of damage to the left aileron. There were no other logbook entries that mentioned the left wing or left aileron.

Metallurgical analysis of the aileron hinge bracket revealed two fatigue fracture origins that led to two regions of final overstress fracture. The fatigue fractures occurred under low stress over an extended period of time. No anomalies were noted in the origin regions and there was no specific evidence of bending at the fracture area. Since there was no specific evidence of bending, it could not be determined if the previous damage to the wing tip resulted in unidentified stress to the fracture area. Wing tip damage as a result of hangar rash could have resulted in residual tension in the aileron tube and precipitated the low-stress fatigue fracture; however, the severity of previous damage to the wing tip and whether the aileron was affected could not be determined.

Text from the NTSB. Open the NTSB docket for CEN17LA344 for the full record.