What happened
On 1 May 2021, an Edge 540, registration G-EDGY, was performing a planned aerobatic routine over the disused Tempsford Airfield in Bedfordshire. The pilot was executing a series of maneuvers, including a vertical climb and a stall turn, when the aircraft was subjected to approximately 5 to 6 g during a recovery from a dive.
As the pilot initiated an aileron roll to the left, a loud bang was heard, and the right aileron began to fail. The control input caused the centre hinge attachment to fail, leading the aileron to bend upwards and partially detach from the wing. Although the aircraft felt heavy in roll and the pilot was concerned about potential jamming, the remaining control authority allowed for a safe return to Little Gransden Airfield. The pilot performed a landing at a higher speed than usual to compensate for the single aileron and landed without further incident.
The investigation
An AAIB field investigation examined the aircraft and the detached aileron components. The investigation focused on the centre hinge attachment assembly of the right aileron, which consisted of two aluminium 'L' shaped brackets.
Metallurgical analysis conducted at a specialist laboratory revealed that the failure was caused by multi-origin fatigue cracks developing in the corner radii of the brackets. The examination of the left aileron's centre hinge revealed similar, though less advanced, cracking. By analyzing striation marks under a scanning electron microscope, investigators estimated the hinge had undergone approximately 14,000 load cycles prior to the failure. This figure was consistent with the owner's estimate of roughly 23,000 full-deflection left rolls performed over the aircraft's life.
Findings
- The right aileron centre hinge attachment failed because fatigue cracks had progressed to a point where the parts could no longer support the flight loads.
- The cracks originated from multiple points, suggesting they were not caused by a specific material flaw or manufacturing defect.
- The left aileron hinge showed evidence of similar fatigue cracking, indicating a systemic issue with the component under repeated loading.
- Routine inspections had not identified the developing cracks, partly because the hinge assemblies are difficult to inspect without removal.