What happened
On 1 August 2017, a Rockwell Commander 114, registration G-TWIZ, was performing a private flight departing from Lydd Airport, Kent. Shortly after takeoff from Runway 21, the pilot attempted to retract the landing gear. While the gear lever was moved to the up position, the green light for the left main landing gear remained illuminated, indicating the gear had failed to retract. Despite several attempts to cycle the gear, the left mainwheel remained extended, though the pilot was able to confirm the gear was down and locked upon return to the airport.
During the landing roll on Runway 21, the left main landing gear leg folded inwards. The aircraft subsequently came to rest on the grass adjacent to the runway. There were no fatalities and no injuries to the two occupants. The aircraft sustained damage to the left wing and the left cabin access step.
The investigation
AAIB investigators examined the fractured left main landing gear upper side-brace. Metallurgical analysis of the component, which was manufactured in 1977, revealed that a fatigue crack had started at a 'cold shut' casting defect. This defect occurred when liquid metal solidified prematurely during the manufacturing process. The crack had progressed to cover approximately 14% of the side-brace's cross-sectional area before the component ultimately failed due to ductile overload.
Further examination of the casting revealed additional internal and surface-breaking defects, as well as sand particles within the metal. Although the component was classified as a 'Class 1A' casting—which mandates radiographic (X-ray) inspection to detect such flaws—the defect was large enough that it should have been identified during the original manufacturing process.