What happened
On 8 June 2004, a Boeing 777, registration AP-BGK, arrived at Stand 210 of Manchester Airport on a passenger flight. Upon reaching the stand, the aircraft's marshaller noticed smoke and fire originating from the left main landing gear. The Manchester Airport Fire Service responded to the scene and successfully extinguished the flames. There were no injuries to the 3/303 passengers or the 13 crew members on board. A post-incident inspection revealed that the brake, axle, and wheel bearings had been blackened by smoke, and the hydraulic lines within the braking system had sustained heat damage.
The investigation
The investigation examined the circumstances surrounding this event and several previous incidents involving the same operator. Records showed that four similar events had occurred recently, involving both the subject aircraft and another Boeing 777, registration AP-BGJ. All these incidents involved wheel assemblies that had been serviced by the operator's engineering department in Karachi using NYCO 22 grease.
Investigators compared the grease used with the requirements of the Aircraft Maintenance Manual (AMM). While the AMM specifies the use of MIL-PRF-81322 specification grease—such as Aeroshell 22 or Mobil 28—the operator had been using NYCO 22, which was common across their other aircraft fleets but not specifically approved for the Boeing 777. Furthermore, the manufacturer had previously issued a maintenance tip warning that fires in the wheel and brake area could be caused by the ignition of excessive grease accumulation in the brake assembly cavity or on the axle.
Findings
- The fire was caused by the ignition of excessive grease accumulated in the brake assembly or on the axle.
- The operator's engineering department had been using NYCO 22 grease for wheel bearing lubrication, which was not specifically authorized for use on the Boeing 777.
- The maintenance practice involved applying more grease than necessary, contrary to manufacturer recommendations which suggest only a thin layer is required at the wheel/axle interface.
Safety action
Following the investigation, the operator ceased the use of NYCO 22 grease, switching to the AMM-specified Aeroshell 22. All wheel assemblies previously serviced with the unapproved grease have been replaced. The operator's engineering department has also implemented instructions to minimize grease application during maintenance to align with manufacturer guidance.