What happened
On July 23, 2011, a Boeing 737-300, registration G-CELD, operated by Jet2.com, was on final approach to runway 27R at Paris Charles de Gaulle Airport. The flight originated from Leeds/Bradford, United Kingdom.
Upon touchdown at a ground speed of 129 knots, the crew immediately experienced violent vibrations, particularly noticeable through the rudder pedals. As the aircraft decelerated, the lateral load factor fluctuated significantly, reaching a peak of 0.8 g at 9 and then decreasing as the speed dropped. The aircraft's trajectory began to deviate toward the right side of the runway centerline, reaching a maximum lateral offset of approximately 10 meters before the oscillations abruptly ceased at 75 knots. The aircraft eventually exited the runway via taxiway Z3 and was subsequently towed to its parking position. Inspection revealed significant damage to the right main landing gear, specifically involving the failure of the lower torque link.
The investigation
The investigation focused on the maintenance history of the aircraft, as the landing gear had been completely replaced the previous day at the operator's maintenance center in Leeds/Bradford. Investigators discovered that during the installation of the new right main gear, the hydraulic line for the shimmy damper had not been reconnected to the aircraft's hydraulic system. Instead, a metal plug had been left in the supply fitting to maintain system pressure.
Testing performed after the gear replacement—which involved cycling the gear while the aircraft was on jacks—failed to detect the error because these tests do not subject the shimmy damper to the hydraulic pressures or mechanical stresses present during landing.
Further examination of the maintenance environment revealed that the maintenance team was managing three aircraft simultaneously, exceeding their planned capacity. This unexpected workload led to a lack of coordination and high time pressure. Additionally, the supervisor responsible for verifying the work had been working excessive hours, leading to fatigue and diminished oversight capabilities.
Findings
- The primary cause of the accident was the omission of the shimmy damper hydraulic reconnection during the landing gear installation.
- High-speed vibrations during the landing roll could not be dampened, leading to the structural failure of the lower torque link.
- Maintenance workload exceeded available personnel capacity, creating time pressure that resulted in errors and approximations.
- The supervisor's performance was compromised by fatigue due to excessive working hours.
- The Boeing maintenance task card in use at the time did not specifically instruct technicians to reconnect the shimmy damper hydraulic lines, only to reconnect hydraulic lines generally.
Safety action
Following the accident, Jet2.com implemented several safety improvements, including:
- A new procedure for managing hydraulic and pneumatic plugs, requiring visible identification tags and a logbook system to ensure all plugs are removed after maintenance.
- Updates to landing gear maintenance task cards to specifically require verification of the shimmy damper hydraulic connection and to mandate an independent check by a second supervisor.
- New fatigue management protocols, including a 4-days-on/4-days-off schedule and strict limits on weekly working hours.
Boeing also issued temporary revisions to the Aircraft Maintenance Manual (AMM) for the B737-300/400/500 series, specifically requiring the reconnection and bleeding of the shimmy damper hydraulic lines.