What happened
On 26 March 2009, a Diamond DA 42 Twin Star, registration G-OCCX, was performing a training flight at Cranfield Airport in Bedfordshire. The flight involved a student pilot practicing an asymmetric approach into runway 21 amidst a 7 kt crosswind from the right. During the landing, the instructor noted that while the approach was initially normal, the crabbed alignment was not corrected. The aircraft touched down on the left main wheel and began drifting toward the left side of the runway.
Immediately upon touchdown, the left main landing gear collapsed. This caused the aircraft to veer off the runway and come to rest on the grass, approximately 8 metres from the runway edge. Following the excursion, the instructor shut down both engines and the electrical systems. The two occupants, both crew members, were uninjured and exited the aircraft via the cockpit canopy.
The investigation
The investigation focused on the structural integrity of the landing gear assembly. The aircraft sustained damage to the left wing, the left engine, the left propeller, and the left main landing gear.
Technical examination of the failed gear revealed that the attachment of the side brace to the primary structure had failed. Specifically, the separation of the GRP assembly from the aircraft showed that two of the three inspection holes had been drilled into an area where a bond defect existed. The investigation found a large void—representing roughly one-third of the surface area—between the upper flange of the assembly and the underside of the wing skin, where the necessary bonding paste was absent.
Findings
- The collapse of the left main landing gear was caused by a failure in the bond between the side brace attachment assembly and the wing skin.
- A significant void existed in the bond area, which had been identified by a previous inspection.
- Although the mandatory inspection procedure (MSB 42-031) had been performed on G-OCCX, the required repair/reinforcement procedure for discovered voids had not been implemented.
- The failure was directly attributed to the absence of the required structural reinforcement following the detection of a bonding void.