What happened
On 24 August 2002, a Cessna 310R Seneca, registration G-SOUL, was conducting a multi-engine piston rating training flight at Nottingham Tollerton. During a practice short field approach on Runway 2/1, the aircraft touched down approximately 50 feet beyond the runway threshold. The weather was clear with good visibility and no wind.
As the pilot applied gentle braking to reduce speed, the aircraft began to veer toward the left. The aircraft eventually slewed 270 degrees to the left before coming to a halt. There were no injuries to the two crew members on board, though the aircraft sustained damage to the left main landing gear, the gear door, and the left wheel and tyre.
The investigation
Investigators examined the left main landing gear and discovered that the torque links had become disconnected at the centre joint. Specifically, the head of the bolt at the torque link centre hinge had pulled through both the washer and the torque link itself. This failure allowed the upper and lower links to separate, which subsequently caused the bolt to pull the bush out of the link.
Technical analysis of the damaged washer revealed that while its dimensions were correct, its material strength was significantly deficient. Hardness tests showed the strength of the failed washer was only 31 tonf/sq in, far below the required minimum specification of 55 to 67 tonf/sq in. It was not possible to determine the origin of this specific part.
Further investigation into the manufacturer's records revealed that the part number in use had been superseded by a thicker, improved version, but this update was not reflected in the current Illustrated Parts Catalogue, nor had operators been formally notified of the improved part's availability.
Findings
- The primary cause of the accident was the disconnection of the torque link centre joint on the left main landing gear, which caused the wheel to castor and led to a loss of directional control.
- A critical contributing factor was that the washer under the bolt head possessed a material strength well below the required specification, allowing the bolt head to pull through the washer under standard landing loads.
- The aircraft manufacturer subsequently agreed to update the Illustrated Parts Catalogue to include the newer, thicker washer part number.