What happened
On 12 October 2012, a Diamond DA42NG Twin Star, registration A6-HIC, was conducting a training flight from Al Ain International Airport with a student pilot and an instructor on board. During the initial climb phase, shortly after establishing a positive rate of climb, the instructor noticed an unusual and increasing noise coming from the rear of the aircraft.
Upon investigation, a gap was observed between the door sill and the lower edge of the passenger door. The instructor attempted to manually hold the door handle to maintain the door's position; however, the intense aerodynamic loads made this impossible. While the aircraft was performing a left turn to join the circuit at approximately 400’ AGL, the rear passenger door separated from the airframe. The instructor took control of the aircraft to manage the high power demands and non-uniform aerodynamic loads caused by the missing door. The aircraft was subsequently able to land safely without further incident.
The investigation
Investigators examined the wreckage and the door assembly to determine how the separation occurred. The investigation established that the passenger door detached as a complete unit. Analysis of the door hinges revealed damage consistent with a failure that exceeded the design limit load. Furthermore, the gas-operated strut, which is intended to support the door in the open position on the ground, failed under the aerodynamic pressure encountered during flight.
Physical evidence on the fuselage, including an abrasion line, indicated that the door had lifted upward against the airframe before the hinges failed. The investigation also reviewed the aircraft's maintenance and the manufacturer's history regarding similar incidents involving the DA40 and DA4/NG series.