What happened
On 12 May 2018, a Piper J3C-65 Cub, registration G-CGIY, was conducting a private flight from Gamston Airport to Leeds East Airport. While en route, the pilot experienced vibrations through the rudder pedals, followed by an uncommand to yaw and a significant jolt. Shortly after, a loud bang occurred, accompanied by a violent nose-down pitch.
Upon regaining control, the pilot noted heavy stick forces and found it necessary to apply constant pressure to the rudder pedals to prevent them from oscillating. A visual inspection revealed that the rudder had become displaced to the right and had partially detached from its upper hinge. The pilot declared the situation to air traffic control and elected to land at Leeds East on Runway 24. The aircraft landed without further incident, and no injuries were reported.
The investigation
Investigators examined the aircraft and found that the upper hinge pin and bearings were missing. The lower hinge lug had also detached from the rudder's leading edge, leaving the rudder held in place solely by the control cables. This instability caused the rudder to oscillate in the slipstream, which damaged the inboard edge frames of both elevators.
Technical analysis of the hinge assembly revealed that while a washer was present at the lower end of the pin, the specified washer that should sit directly under the head of the pivot pin was absent from the upper hinge. Because the diameter of the pin head was slightly smaller than the outer diameter of the bushes, there was nothing to prevent the components from working loose.
Findings
- The partial rudder detachment was caused by the loss of the upper hinge pin and bushes.
- The loss of these components was made possible because the required upper washer was not installed.
- The absence of the washer allowed the pin and bushes to migrate out of the hinge assembly.
- The resulting rudder oscillation caused structural damage to the elevator ribs and distorted the lower hinge lug.
- A random inspection of other similar aircraft identified two other examples missing the same upper washer, suggesting a potential fleet-wide assembly issue.
Safety action
- The CAA has been notified and is evaluating necessary safety actions for owners and operators.
- The LAA has issued safety advice to Cub owners regarding the correct assembly and integrity of rudder hinge pins.