What happened
On 28 April 2016, a Diamond DA42 Twin Star, registration G-CTCB, was completing a training flight at Bournemouth Airport. The flight involved a student pilot in the left seat, an instructor in the right seat, and a student passenger in the rear. The approach to runway 26 was conducted as a practice asymmetric power approach, with the left engine idling at approximately 18% power.
As the aircraft touched down, the instructor noted a firm landing. Shortly after contact with the runway, a continuous beeping sound began, which the crew identified as the landing gear 'unsafe' warning. The left main gear green light was extinguished, and the red warning light was flashing. The instructor took control and taxied the aircraft to a nearby taxiway. Upon stopping and shutting down the engines, the crew discovered that the left main landing gear leg had partially collapsed. There were no injuries to the two crew members or the passenger.
The investigation
The investigation focused on the structural integrity of the landing gear assembly. Examination of the aircraft revealed that the composite drag brace rib, which connects the left main landing gear drag brace to the centre wing section, had detached.
Technical analysis by the aircraft manufacturer determined that the failure was caused by an overload failure of the bonding between the composite rib and the composite centre wing section. The manufacturer's examination suggested that the component had sustained damage during a previous hard sideslip landing, which eventually led to the final separation during the landing on 28 April.
Records indicated that a Mandatory Service Bulletin (MSB-42-031/1) regarding the inspection and repair of this specific bonding had been performed on this aircraft in 2007. Physical evidence suggested that this specific repair had been executed correctly.