What happened
On 8 October 2016, a Flight Design CTSW, registration G-CGVG, was taxiing across a grass parking area at Hunslot Airfield, Hertfordshire, following a routine landing on grass Runway 03. During the taxi, the aircraft's left main landing gear leg suddenly collapsed. The impact caused the aircraft to settle onto its left wingtip, resulting in damage to the wingtip, the left landing gear leg, and the surrounding fuselage structure. The pilot and one passenger were both uninjured and were able to exit the aircraft safely.
The investigation
Investigators examined the left main landing gear leg, which consists of a tapered 7075-T6 aluminium alloy beam. The examination revealed that a fatigue crack had originated at the aft lower edge of the main attachment bolt hole. This crack had progressed through approximately 60% of the thickness of the lower section of the leg before the component ultimately failed due to ductile overload. The investigation also noted damage to the left fuselage skin and the delamination of the left rear reinforcement plate, caused by the upward rotation of the gear leg during the collapse.
Regarding maintenance history, the aircraft's logbook for the period in question was unavailable because it had been lost during a burglary. While the aircraft's operator manual requires dye penetrant testing of the landing gear legs every 300 flying hours, it was unclear if this specific inspection had been performed. Because the aircraft was manufactured in 2011, it was not subject to the one-time inspection mandated by Service Bulletin CT123, which applied only to aircraft built before February 2007.
Findings
- The left main landing gear leg failed because of a fatigue crack spreading from the rear edge of the main attachment bolt hole.
- The aircraft was not required to undergo the specific one-time inspection outlined in SB CT123 due to its 2011 manufacture date.
- It could not be confirmed if the 300-hour in-situ inspection required by the operator's manual had been completed due to missing maintenance records.
- No heavy landings had been reported that would have necessitated an inspection under existing service bulletins.
Safety action
Following the accident, the UK agent announced plans to issue Service Bulletin CT145. This new bulletin will require the removal and dye penetrant inspection of the main landing gear legs on all CT2K and CTSW aircraft every 300 flying hours. The new bulletin will also introduce a modification to peen the edges of the main attachment holes to help prevent the initiation of fatigue cracks.