Incident Details
On February 15, 2011, at 0930 central standard time, a Beech E-90 airplane, registration N51DN, sustained substantial damage when the right aileron departed the aircraft in-flight near Des Moines, Iowa. The airplane was operated by D-W Corporation of Des Moines, Iowa, under 14 Code of Federal Regulations Part 91 as a local test flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight departed Des Moines International Airport (DSM) at 0900.
The airplane had recently undergone maintenance, including an 800-hour inspection of the ailerons that required removal, reinstallation, and a functional check. Prior to the test flight, the pilot performed a preflight inspection and a flight control free and correct check, noting no anomalies.
After departure from runway 13L, the pilot turned right to 160 degrees, then right to 270 degrees, and was cleared to flight level (FL) 180. While level at FL180 with the autopilot engaged, the pilot and a pilot-rated maintenance crew member conducted various checks of the engines and flight instruments. Following these checks, the pilot requested and received approval for a left 180-degree turn back to DSM. During the turn, approximately 140 degrees into the turn, the autopilot jerked, stabilized, and jerked again as the aircraft leveled off. The pilot then observed that the right aileron had separated. The aircraft landed at DSM without further incident.
Examination Findings
Post-flight examination revealed that the inboard and middle airframe aileron hinge brackets remained attached to the aft spar, intact and without visible damage. The outboard airframe aileron hinge bracket had pulled away and separated from the aft spar. The aileron itself was not located.
The aileron is attached to each of the three hinge brackets using two upper and two lower bolts (four total) that engage into nut plates mounted on the aileron. The King Air 90 Series Maintenance Manual aileron installation procedure specifies: "Carefully align the three hinges with the aileron and install the bolts in each hinge bracket and the aileron. Pull on the aileron straight away from the wing. If any movement is detected, carefully check the bolt installation."