Incident Overview
On 8 June 2004, at approximately 0850 UTC, a Boeing 777 aircraft, registration AP-BGK, arrived at Stand 210 at Manchester Airport. After the aircraft came to a stop, the marshaller observed a fire originating from the left main landing gear. The Airport Fire Service attended and extinguished the fire. No injuries were reported among the 13 crew and 303 passengers. Subsequent examination showed that the brakes, axle, and wheel bearings had been blackened by smoke, and the hydraulic lines in the braking system sustained heat damage.
Aircraft Configuration
The Boeing 777 has two main landing gear, each with three pairs of wheels. Wheels are numbered from left to right; the front outboard left wheel is number 1 and the rear right outboard is number 12. In this incident, wheel position No. 9 was affected.
Related Events
The operator reported two previous similar events involving another Boeing 777 (AP-BGJ) on 27 May 2004 at Manchester and on 4 June 2004 at Toronto. A further event occurred on 9 June 2004 on AP-BGJ at Manchester. In all cases, the affected wheel assemblies had been replaced at Karachi by the operator's engineering department using NYCO 22 grease. The aircraft maintenance manual (AMM) for the Boeing 777 specifies grease meeting specification MIL-PRF-81322, such as Mobil 28, Aeroshell 22, or Mobil Aviation Grease SHC100. NYCO 22 grease meets the MIL-PRF-81322 specification but was not specifically approved for the Boeing 777, although it was in general use on other aircraft types operated by the company.
Manufacturer Guidance
The aircraft manufacturer had published Maintenance Tip 777 MT 32-021 (dated 29 May 2001) noting that wheel/brake-area fires are occasionally reported following normal operating brake temperature condition landings. The tip indicated that the cause of such fires can be attributed to ignition of excessive grease that has accumulated in the brake assembly cavity and/or on the axle. Also, residual cleaning fluids can be retained by some wheel heat shields after being saturated with flammable solvents during maintenance. Wheel/brake-area fires have also been reported due to ignition of hydraulic fluid associated with leaks or hydraulic system maintenance. The manufacturer recommended that during wheel and brake removal/installation, old grease be removed from the axle using a dry rag, and that only a thin layer of grease be applied at the wheel/axle interface. Similarly, a thin layer of grease should be applied to the interface surfaces of the brake and axle sleeves. Additionally, operators should assure that the brake axle bushing grease seal (on airplanes that have them) is not damaged prior to brake installation and is properly installed per applicable instructions.
Operator Follow-up
The operator discontinued the use of NYCO 22 and switched to Aeroshell 22 as specified in the AMM. All wheel assemblies previously fitted by the operator's engineering department were replaced with items assembled using Aeroshell 22. All line stations were instructed to use Aeroshell 22 on all fleets and discontinue the use of NYCO 22 grease. Additionally, the operator's engineering department minimized the application of grease as recommended by the manufacturer. No further incidents have been reported.