What happened
On 14 March 2013, a Cessna 402B Utililiner, registration G-NOSE, was conducting an aerial photography mission in the Swindon area. The flight crew, which included a pilot, an observer, and a photographer, was in the process of returning to East Midlands Airport.
As the aircraft descended from 5,800 feet to 4,000 feet, the airspeed increased from 14 and 170 kt. While passing through 4,500 feet, the pilot experienced a sudden loud bang and a noticeable change in cabin air pressure. The pilot subsequently realized that the right-hand emergency exit door had detached from the aircraft. The pilot declared a PAN-PAN urgency signal and reduced the airspeed to 140 kt. The detached door was later located on a driveway of a private residence in Shrivenham. There were no injuries to the crew or passengers, though the aircraft sustained minor damage to the door aperture.
The investigation
The investigation focused on the mechanical integrity of the door and the release mechanism. The right emergency exit door was a windowed panel secured by two locking pins. These pins are held in place by shear pins, which are designed to break only when the door release handle is pulled.
An inspection of the aircraft structure and the door's attachment points showed no signs of wear or defects that would permit accidental release. The operator's inspection confirmed that the release handle had remained in its secure position and the 'tell-tale' wire, intended to indicate movement of the lever arm, was still intact. Furthermore, the shear pins were found to be in place.
Findings
- The aircraft was performing a routine descent following an aerial photography sortie.
- The right emergency exit door separated from the fuselage while the aircraft was at 4,500 feet.
- No recent maintenance had been performed on the door assembly.
- The relative movement between the door and the aircraft structure, combined with dynamic flight loads, may have been sufficient to disengage the locking pins and release the door.