Guy Norris/LOS ANGELES
Pratt & Whitney and General Electric are inspecting their respective PW4090 and GE90 engines for the Boeing 777, after a new series of problems with powerplants on British Airways and United Airlines aircraft.
The GE90 suffered a crack in a rotating seal on the high-pressure compressor (HPC), between the second and sixth stage, which was unearthed during routine maintenance on a high-time test engine at Evendale, Ohio.
GE says that, by 23 October, some 31 engines with factory, flight and production test and revenue service experience had been inspected, and one engine, on a BA 777, had been removed with a seal crack. Further inspections on the remainder of the fleet are due to be completed by early November.
The P&W problem was discovered more dramatically when an engine had to be shut down in flight after a "large bang" was heard as the United 777 rotated on take-off from London Heathrow Airport in the UK.
Another incident, not severe enough to warrant an in-flight shut down, was also experienced on another United aircraft shortly after take-off from Los Angeles International Airport in the USA.
The engines involved are being stripped down and inspected to find the cause, although P&W says: "It appears that they were unique incidents. We don't think we have a fleet-wide problem." Investigations are believed to be centred on bearing seals in the base of the engine, particularly since the powerplant in the Heathrow event generated a low-oil warning.
GE, meanwhile, seems closer to defining the cause of the HPC cracking in a seal tooth as an "undesirable seal rub condition". The company believes that the condition will be eliminated by "a minor modification of the adjacent honeycomb shroud, which is designed to make contact with the rotating seal". GE adds that metallurgical analysis confirms that the crack is "-stable and its growth rate is not accelerating". It also says the condition will be controlled through a periodic inspection programme".
P&W's higher-thrust PW4098 engine has passed a critical fan-blade containment test at East Hartford, Connecticut.
The test was the fifth in a series of 13 major certification requirements for the engine which is due to receive certification from the US Federal Aviation Administration in March 1998 for the higher-weight variant of the 777-300.o
Source: Flight International
