What happened
On 17 October 1998, a Cessna 340, registration N340YP, was conducting a private training flight when the pilot encountered an issue with the landing gear shortly after takeoff from Biggin Hill Airport, Kent. The pilot discovered that the gear could not be raised and subsequently decided to return to the airfield immediately.
The return to the airport proceeded without incident until the aircraft was turning off the runway after landing. At that moment, the pilot experienced a jarring sensation originating from the left side of the aircraft. Once the aircraft had cleared the runway, the engines were shut down for inspection.
The investigation
Investigators examined the aircraft and identified damage to the left main landing gear door. The inspection established that the torque link knuckle joint had separated. This separation allowed the wheel to caster, which directly resulted in the minor damage to the gear door.
Findings
Technical analysis revealed that the failure was caused by the use of an insufficiently substantial washer positioned under the head of the knuckle bolt. Over time, this washer had worn or distorted during service. This degradation allowed the bolt head to migrate through the bore of the scissor link, pulling the knuckle bush along with it until the joint between the two halves of the scissor link eventually separated.