THE GENERAL ELECTRIC GE90-powered Boeing 777 reached Mach 0.96 during a high-speed dive in February, as part of a faster-than-expected expansion of the aircraft/engine flight envelope.
"We are well into the test schedule. In fact we're already at the point that we'd normally be at six weeks into a programme like this," says Boeing. By the end of February, the GE90-powered 777 had amassed around 40h of flight time since its first flight on 2 February, and reached a maximum altitude of 43,000ft (13,000m).
More than 150h of ground running have also been achieved. "The aircraft is performing extremely well. We completed flutter testing in one day, which is much shorter than usual, and we did more engine tests on the same flight."
GE, meanwhile, is running new flight tests of a GE90 on its Boeing 747 testbed from Mojave, California, to pre-empt any possible performance anomalies which may crop up in the 777 tests.
GE CF6 and GE90 marketing development manager Vince DiGiovanni says that the flight tests include "...some deliberately high angle-of-attack stalls to verify operability of the engine within the envelope". The engine has so far proved stall-resistant. "All the JT9Ds on the testbed were stalling, while the GE90 kept going," he says.
The supplemental 747 test programme is seen as GE's insurance against any further delays hindering the certification timetable. "We will certificate on schedule in August, with deliveries beginning immediately afterwards to British Airways," says DiGiovanni.
Meanwhile, US 777 engine rival Pratt & Whitney is awaiting a decision from the US Federal Aviation Administration on whether the PW4084/777 extended-range twin-operations (ETOPS) effort will be affected by an unscheduled engine removal from test aircraft WA004. The engine was just 35 cycles short of the 500-cycle goal when it seized during aground run on the Boeing flight line.
Human error is blamed for the incident, which occurred after the engine oil had been drained for an oil change. Standard procedure is to "turn the motor" to scavenge the last of the oil out of the bearings, but a Boeing mechanic is believed to have run the dry engine for more than 3.5min, after which it seized. The engine has been returned to P&W's Hartford plant in Connecticut for an "analytical teardown, with the FAA looking on", says the engine maker.
P&W is "quietly optimistic" that the incident will not cause the FAA to require any changes to the ETOPS programme. The affected engine had already amassed 2,000 cycles of ground running before being flown on WA004 and had run up "about 100 extra flight cycles" before the ETOPS programme officially began.
Fast progress in the flight-test programme means that one of the 777 test fleet, WA003, is to be pulled out of flight-test work for earlier-than-planned refurbishment. The aircraft has amassed more than 425 flight hours and 224 flights and will be fitted out with a complete interior over the next three months. Total time on the P&W-powered fleet now exceeds 2,230h and 2,620 flights.
Source: Flight International
