Guy Norris/LOS ANGELES
PLANS TO BEGIN extended-range twinjet-operations (ETOPS) tests of the General Electric GE90-powered Boeing 777 have been hit by an incident in which a British Airways aircraft suffered an engine surge during pre-delivery flight tests.
Although the engine recovered automatically from the surge, which occurred during stick-shaker tests on aircraft WA080 flying at a high angle of attack, the resulting damage to the fan-rub strip and fan blades themselves was worse than expected. Boeing says that "...the engine was bore-scoped and there was no significant damage to the core, but they did find rubbing on the fan".
By chance, the incident occurred just two days before the US Federal Aviation Administration reliability-assessment board (RAB) sat to discuss ETOPS plans for the GE90- and Rolls-Royce Trent- powered 777. At the meeting the Boeing/GE ETOPS team proposed a revised plan involving a new 3,000-cycle test, completion of the current 1,000-cycle evaluation and an agreement to conduct an additional review of all the "lessons learned" to date.
Largely as a result of the WA080 incident, the RAB failed to approve the GE90 ETOPS plan and deferred its decision pending "a further review of all available data", says Boeing, which was hoping to begin GE and R-R ETOPS programmes by mid-December. The resulting delay will push back the start of the GE90 ETOPS programme until at least early January.
The GE90-powered 777 was originally scheduled to gain early ETOPS approval in September 1995 and, under the new plan proposed to the RAB, would have achieved this around mid-April 1996. Boeing sources say that the FAA was already considering delaying a decision to January because of the huge amount of technical data on the GE90, which it had to process.
GE is running tests and preparing a series of flight tests to replicate the manoeuvre and evaluate what exactly caused the surge. GE says: "It's too early to determine a cause." The company hopes that he investigation will show the incident to be a "one-off" related to a quality-control issue.
Progress on the Trent/777 ETOPS "...appears to be going well and to plan", says Boeing.
Source: Flight International
