Grease Is the Word In Wheel Fires

Air Safety Week, March 7, 2005

Another PIA B777 'Takes Up Smoking' In UK

Perhaps that well-known aviator John Travolta, an expert on "grease," could be of assistance to Pakistan International Airlines (PIA). They seem to have a persistent problem with grease causing wheel-brake fires on their Boeing [BA] B777s. In the latest instance, Flight PK789 from Karachi was taxiing in when a fire started in its left main undercarriage. The flight had landed at 0903GMT and was about to disembark its load at Terminal 2 at Manchester, UK, when a following aircraft reported the fire. Fire-crews reported assisting 340 passengers and 12 crew to evacuate down slides. (PIA disputed the number on board, saying it was only 232.)

In Pakistan, the chief of the airline's engineering department attributed the incident to a greasing problem in B777 wheels. "This is the fifth incident of similar fire with our Boeing 777 and the matter was reported to the manufacturer,"' Mukhatar A. Qazi told The Associated Press. "They changed the lubricant quality and quantity but even then, this has happened."

His angst is understandable. Two similar incidents happened on successive days last June. On June 8, 2004, after the aircraft arrived on stand at Manchester Airport, the marshaller observed a fire originating from the left main landing gear. Subsequent examination of the brakes, axle and wheel bearings showed that they had been blackened by smoke. The hydraulic lines in the braking system had sustained heat damage.

The UK Aircraft Accident Investigation Board (AAIB) was notified of a similar event the following day and the operator reported two previous events. The known details of all the incidents to date are as follows:

Incident Date  Aircraft Registration  Location
May 27, '04    AP-BGJ                 Manchester, UK
June 4, '04    AP-BGJ                 Toronto, Canada
June 8, '04    AP-BGK                 Manchester
June 9, '04    AP-BGJ                 Manchester
March 1, '05   AP-BGL                 Manchester

Incident Date  Wheel Position  Installation Date
May 27, '04    No 5            May 24, '04
June 4, '04    No 12           May 24, '04
June 8, '04    No 9            June 7, '04
June 9, '04    No 6            June 7, '04
March 1, '05   n/a             n/a

Manufacturer Boeing warned in 2001 that excess grease needed to be cleaned from the brakes. PIA had begun operating the 777 in March 2004. All the incidents occurred on wheel assemblies that had been replaced at Karachi, by the operator's engineers, using NYCO 22 grease. The Aircraft Maintenance Manual (AMM) specifies the use of general purpose, wide temperature grease with the specification MIL-PRF-81322 for the wheel assembly. It specifically mentions three types: Mobil 28, Aeroshell 22 and Mobil Aviation Grease SHC100. NYCO 22 grease, which meets the MIL-PFR-81322 specification, was in general use by the operator for lubrication of wheel bearings and was specified as an alternative on other aircraft types. It was not, however, specifically approved for use on the Boeing 777.

The aircraft manufacturer published a Maintenance Tip (777 MT 32-021, dated May 29, 2001) which states:

Wheel/brake-area fires are occasionally reported following normal operating brake temperature condition landings. Typically, the cause of the fires can be attributed to the 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.

It recommends the following action:

During wheel and brake removal/installation, it is important to remove the old grease from the axle. Use of a dry rag is recommended since cleaning fluids and solvents can cause damage to carbon brakes and titanium components. While it is important to have adequate lubrication within the wheel bearings, only a thin layer of grease is necessary at the wheel/axle interface for wheel/tire installations. Similarly, a thin layer of grease is applied to the interface surfaces of the brake and axle sleeves during brake installation. (Note: When applying grease to the axle bushings on the brake assembly, it is important to completely fill the grooves in the bushings with grease.) 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 the applicable AMM or Component Maintenance Manual (CMM) instructions.

PIA has since 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 have been replaced with items assembled using Aeroshell 22. All line stations have been instructed to use Aeroshell 22 on all fleets and discontinue the use of NYCO 22 grease. Additionally, the operator's engineering department has minimized the application of grease as recommended by the manufacturer.