Graham Warwick/ATLANTA
BOEING delivered three General Electric GE90-powered 777s by the end of 1995, after GE's proposed increase of the fan-blade-tip clearances had been approved by the US Federal Aviation Administration (Flight International, 20 December, 1995-2 January, P4). Efforts continued to determine the cause of an engine surge. The aircraft affected are two for British Airways and one for China Southern Airlines.
GE sought US Federal Aviation Administration permission to increase blade-tip clearance by 1.3mm on engines ready for delivery, after the 3 December surge (during high-angle-of-attack flight testing) was attributed to heavy rubbing of the composite fan blades against the fan-case abradable seal.
As of mid-December, GE had been unable to replicate the rub problem in ground tests of the fan and fan-case module removed from the affected engine. The manufacturer believes that the surge may have been a one-time event unique to that module.
The module was replaced and Boeing made a "flawless" acceptance flight with the aircraft, BA's third 777. GE nevertheless planned to increase blade-tip clearances on GE90s powering this and two other aircraft, BA's second 777 and China's Southern first, as a precaution and to allow their delivery by the end of 1995.
The FAA's Reliability Assessment Board will decide in mid-January whether the GE90 is ready to proceed into 1,000-cycle extended-range twinjet-operations testing. GE says, that BA has logged 1,000 engine hours in the first 50 flights, of its first 777 "with zero problems".
Source: Flight International
