Beech 90B N37OU incident near Chickasha, Oklahoma

Probable cause

The mechanic's improper installation of the aileron.

NTSB analysis

The certified flight instructor (CFI) reported that the airplane was on a downwind leg for landing when a pilot-rated passenger who was sitting in the cabin told him that the right aileron was partially separated from the airplane. The CFI took control of the airplane and landed it uneventfully. The post incident inspection of the airplane revealed that the two inboard aileron hinges were separated from the airframe. The screws (8 screws, 4 upper, 4 lower) which attached the aileron to the aileron hinge points were seated in the aileron skin, but did not screw into the corresponding nut plates on the aileron hinge points. The aileron was not damaged so a mechanic attached the aileron properly to the aileron hinge points and the airplane was returned to service. Maintenance records indicated that the airplane had undergone a phase inspection 10 days prior to the incident. During the phase inspection, the right aileron was removed to repair some light surface corrosion and was reinstalled on the airplane. The incident occurred 5.3 hours after the phase inspection was performed. Eight years prior to the accident, the aircraft manufacturer issued a communique which stated that their technical support department had received reports that during aileron installation, screws missed the nut plates on the aileron hinge points. It stated that this condition can go unnoticed.

Text from the NTSB. Open the NTSB docket for CEN11IA280 for the full record.