What happened
On 13 March 2006, a Piper PA 31-310, registration SE-GIT, was conducting a commercial passenger flight to Umeå airport when the crew encountered a significant technical failure. During the approach to runway 14, the pilots selected the landing gear down, but the cockpit indicators failed to confirm that the left main landing gear was locked.
After performing several attempts to cycle the gear and utilizing emergency extension procedures, the crew remained unable to secure the gear in the down position. Ground observations from the control tower revealed that the left landing gear door was stuck approximately 45 degrees open. To mitigate the risk of fire from potential sparks on asphalt, the commander elected to perform an emergency landing on a snow-covered area adjacent to the runway. The aircraft touched down with the gear retracted and full flaps deployed, sliding 192 meters through the snow before coming to a stop. All eight occupants, including the crew, escaped without injury.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the mechanical state of the landing gear and the structural integrity of the door assemblies. The investigation focused on the hydraulic mechanism and the physical condition of the hinge assemblies. Investigators also reviewed the maintenance history and previous repair work performed on the landing gear doors.
Findings
Technical analysis revealed that fatigue cracks had developed in the front hinge assemblies of both main landing and landing gear doors. During the extension sequence, the front hinge assembly on the left door fractured completely. This failure caused the door to hang at an angle that obstructed the gear's movement. Furthermore, the hydraulic actuating rod became bent while attempting to move the fractured door, which subsequently jammed the mechanism and prevented the left main gear from reaching the locked position.
Safety action
To prevent similar occurrences, the investigation concluded that the primary cause was an inadequate directive regarding the inspection of these specific hinge assemblies. It is recommended that EASA implement requirements for the periodic inspection of these hinge assemblies to detect crack generation before structural failure occurs.