What happened
On 1 June 2022, a Cessna Citation 560XL, registration EC-KPB, was performing a commercial air transport flight when the aircraft's nosewheel detached during taxiing at RAF Northolt. Following a routine landing, the crew reported hearing an unusual noise, immediately followed by the sensation of the front of the aircraft dropping. The nosewheel separated from the nose landing gear leg and rolled into the grass adjacent to the taxiway, leaving the gear forks resting directly on the pavement.
There were no fatalities and no injuries to the two crew members or the three passengers on board.
The investigation
The investigation focused on the mechanical integrity of the nose landing gear assembly. The nosewheel assembly had been in service for 337 flying hours and 230 cycles since its last replacement in September 2021. While the assembly had been reconditioned according to the manufacturer's manual prior to installation, the exact condition of the bearings used during that reconditioning could not be confirmed.
Laboratory analysis of the wheel assembly revealed that one of the conical bearings had failed. Although the damage to the failed bearing was too extensive to pinpoint a specific cause, examination of the remaining functional bearing showed significant material pitting and corrosion around the shoulder and along the rollers. This pattern suggested corrosion had occurred while the component was stationary. While grease was present in the wheel cavity, the heat generated during the failure had burnt off much of the lubricant from the failed bearing components.
Findings
- The primary cause of the separation was the failure of a conical bearing within the wheel hub.
- The failure sequence likely began with corrosion pitting in the bearing races, leading to the disintegration of the bearing cage.
- This failure caused the rollers to skid, generating intense frictional heat that led to the bearing seizing and the axle spinning within its supports.
- The resulting heat and lateral loading caused the axle to migrate and eventually snap the through bolt, allowing the wheel to twist out of the forks.
- Evidence of corrosion on the non-failed bearing suggests that the failed bearing was likely subject to similar corrosive processes, though the origin of the corrosion could not be determined.