What happened
On September 11, 2007, a DHC-8-402, registration LN-RDS, operated by Scandinavian Airlines System (SAS), was performing a scheduled passenger flight from Copenhagen to Palanga. During the approach to Palanga, the crew attempted to extend the landing gear, but the cockpit indicators showed an abnormal status: the right main landing gear strut was not down and locked, and the gear door was open.
The crew initiated a go-around and attempted to retract the gear, but the warning lights remained illuminated. After consulting with maintenance personnel in Copenhagen, the crew diverted to Vilnius Airport. Despite attempts to use the emergency gear extension system, the cockpit indicators continued to show an unsafe gear configuration. During the approach to Vilnius, the crew operated on only one engine.
Upon touchdown on runway 20 at 22:35 local time, the right main landing gear strut failed to lock and subsequently retracted one second after the aircraft touched the ground. The aircraft then veered off the runway, striking the side of the runway shoulder and coming to a stop approximately 1,150 meters from the threshold. While there were no injuries among the 48 passengers or the crew, the aircraft sustained heavy damage to the right engine nacelle, wing tip, fuselage, and landing gear components.
The investigation
The investigation examined the mechanical failure of the landing gear assembly and the maintenance protocols for the aircraft. Investigators analyzed the right main landing gear strut and found that the rod end of the extension/retraction mechanism had detached from the mechanism shaft. This detachment was caused by corrosion at the threaded connection.
Further examination revealed that when the rod end detached, the free-falling weight of the gear strut broke the connecting links of the stabilizer. This prevented the gear from locking in the extended position and allowed it to retract spontaneously during the high-speed rollout on the runway.
Findings
- The primary cause of the accident was the detachment of the extension/retraction mechanism shaft end due to corrosion at the threaded connection.
- The failure of the stabilizer links caused the right main landing gear to fail to lock and subsequently retract during taxiing.
- The aircraft's maintenance program did not include specific inspections for the landing gear extension/retraction mechanisms.
- The operational life limit (resource) established by the manufacturer for these mechanisms was excessively long, allowing corrosion to develop undetected.