Incident Overview
On March 14, 2019, at approximately 1730 Pacific daylight time, a Great Lakes 2T-1A-2 airplane, registration N101GL, sustained substantial damage during a personal flight near San Diego, California. The private pilot and passenger were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91.
Pilot Report
About five minutes after takeoff, the pilot observed that the left upper aileron had become loose from its inboard hinge, remaining attached only by the outboard hinge. The pilot returned to the departure airport and landed without further incident.
Damage Examination
Post-accident examination revealed substantial damage to a wing rib aft of the spar at the outboard aileron cutout. The failed aileron hinge strap, consisting of two components, was secured and sent to the NTSB Materials Laboratory for analysis.
The pilot noted that the manufacturer did not provide inspection criteria for the hinge straps; however, all hinge straps were inspected annually.
Laboratory Findings
Examination of the fracture surfaces by the NTSB Materials Laboratory technician identified crack arrest marks and thumbnail-shaped patterns (ratchet marks) on both the top and bottom surfaces of the hinge strap. These features indicated asymmetric reverse-bending fatigue crack propagation. The fatigue cracking extended through nearly the entire cross-section of the hinge strap.