What happened
On June 29, 2011, a single-engine Diamond DA 40 D, registration PH-TIN, was conducting a private flight departing from Lelystad Airport. Approximately thirteen minutes into the flight, while cruising at 1,000 feet at roughly 120 knots, the pilot observed an "open door" warning on the primary flight display. Upon inspection, the pilot saw the door handle moving away from the closed position. Within seconds, the passenger door detached from the airframe and flew over the tail section. The pilot immediately reduced speed, notified Lelystad Radio, and performed an emergency return to the departure airfield, landing safely. No injuries were reported, and no damage was sustained by the aircraft, though the door was later recovered from a field near Biddinghuizen.
The investigation
The Dutch Safety Board (OVV) coordinated with the Austrian Aircraft Accident Investigation Branch to examine the detached door. Physical inspections of the aircraft revealed that the rear hinge bracket had broken off, while the front hinge bracket had torn. Investigators examined the locking mechanism, noting that the two locking pins were not engaged in their respective guides in the fuselage. This lack of engagement indicated that the door had not been properly secured using the primary locking mechanism. Furthermore, the investigation looked into the possibility of mechanical failure, but testing by the manufacturer, Diamond Aircraft Industries GmbH, found no evidence of component failure in the door itself.
Findings
Investigation results concluded that the door handle was not in the locked position at the time of the incident. Because the handle was not fully engaged, the locking pins were not seated in the fuselage guides. This allowed the front of the door to move upward, which subsequently deactivated the safety latch. A significant contributing factor was identified as excessive play in the front hinge bracket, which facilitated the door's movement and eventual detachment. While the aircraft had recently undergone a mandatory modification to the safety latch bracket, this modification could not prevent the door from breaking away under these specific conditions of an unlocked handle and hinge instability.