Incident
During a positioning flight, the pilot observed that the airplane required aileron trim to maintain level flight. The airplane subsequently landed without further incident.
Inspection Findings
A post-flight examination of the airplane revealed two missing rivets on the underside of the left wing, located between the heat shield and a factory-installed doubler. The lower forward spar cap was found cracked at wing station (WS) 114, at a rivet hole just outboard of the outboard engine beam. Both the forward and aft web doublers were split near the end of the inboard wing spar web at WS 112.5. Additionally, the skin was cracked from the front spar lower cap up to the first stringer location behind the front spar.
Examination Details
At the time of the incident, the airplane had accumulated approximately 20,510 total operational hours. It was subject to Federal Aviation Administration Airworthiness Directive (AD) 2000-23-01, which required inspections of the forward, aft, and auxiliary wing spars for cracks at intervals not exceeding 110 hours time-in-service.
The cracked portion of the forward spar, skin, and aft web doubler were removed for further examination. This examination revealed fatigue damage that originated at the forward portion of the rivet hole on the spar cap at WS 114. Blackening and corrosion were observed on the fracture surface, consistent with the fracture being present at the time of the airplane's most recent inspection, which had been conducted approximately one week earlier, at 12 operational hours before the incident flight.