What happened
On 7 October 2005, a BAe 146, registration EI-CPJ, was performing a passenger flight when it experienced a significant nose wheel shimmy during the landing roll on Runway 10 at London City Airport. Following a smooth touchdown, the nose wheel began to vibrate violently once it made contact with the runway. As the pilot applied braking to the main wheels, the vibrations intensified. To maintain directional control and mitigate the severity of the oscillation, the crew utilized moderate differential braking to bring the aircraft to a halt as quickly as possible.
Following the stop, the crew issued a PAN call to Air Traffic Control. While the airport Rescue and Fire Fighting Service attended the scene, the crew noted an initial difficulty in communicating with a firefighter using a handheld radio, though communication was eventually established.
The investigation
An inspection by airline engineers and later by specialists from the landing gear manufacturer revealed that a central pivot bolt from the torque link assembly was missing. Although an extensive search was conducted at both London City Airport and the departure airfield, the bolt was not recovered. The investigation established that the loss of this bolt caused the upper half of the torque link to pivot downward, making contact with a shoulder on the lower part of the landing gear. This movement effectively turned the strut into a solid unit, preventing the oleo from compressing under the 2.5-tonne weight of the nose.
Further technical examinations of the nose landing gear assembly identified that the friction damper breakout torque was only approximately 35-40% of the required specification. Additionally, the oleo inflation pressure was found to be roughly 28% above the specified limit, likely as a compensation for internal oil leakage past the seals.
Findings
- The primary cause of the landing roll vibration was the missing anti-torque links central pivot bolt.
- The loss of the bolt caused the torque link to jam, preventing the oleo strut from functioning correctly.
- The nose wheel steering system was found to be inoperative due to the mechanical failure of the torque link assembly.
- The friction damper breakout torque was significantly below the required specification, which likely predisposed the gear to a divergent shimmy oscillation.
- The oleo inflation pressure was excessively high, which was attributed to internal oil leakage past the seals.