Guy Norris/Los Angeles
BOEING AND General Electric are believed to be making contingency plans, for a possible delay in the certification and delivery of the first GE90-powered 777 following a fan-balance problem experienced during ground tests.
Test flying of the two GE90-powered Boeing 777 test aircraft at Seattle, has been suspended since 24 May, following problems with two tests conducted in Europe.
Officially, both companies continue to insist that the September delivery date is still realistic.
GE says that the "greater-than -expected fan imbalance" occurred during two tests to assess the retention qualities of a new aluminium containment ring at higher-thrust levels of 410kN (92,000lb). Both tests were being run in preparation for later certification tests of the higher thrust engine for the initial "B"-market 777.
The first incident occurred during a blade-out test on a whirligig unit at European Gas Turbines in the UK. GE will not comment on reports that the detached blade also damaged trailing blades in the fan assembly.
The second incident happened during a 3.6kg bird-ingestion test at Snecma's site in Villaroche, France. Again, GE declines to comment on speculation that multiple fan blades were badly damaged by the impact. GE says, however that "...the durability of the GE90 composite fan blades and the engine's new, cost-reducing all-aluminum fan casing were further validated."
Although fan imbalances are an obvious result of either test, GE was concerned that the imbalance exceeded the post-blade-off operating tolerances, but only by a small margin. GE believes that a redesign of the aluminium spacer, which occupies the gap between the blade roots, will be sufficient to recover the margin.
"The redesign is in progress and hardware is being modified. GE will then validate the modification, and install the change into all of the flight test engines, before resuming flights," says the company.
The grounding puts pressure on an already compressed certification schedule, which calls for delivery of the first GE90-powered 777 to British Airways on 21 September.
The engine was certificated in February at 380kN, more than two months late, and according to data supplied to Flight International, type certification of the GE-powered 777 was due on 1 August.
The latest events occurred just as the troubled programme was recovering from an incident on 4 May, when an engine surged on take-off because of problems in the scheduling of the variable guide vanes. At the time, the first test aircraft had undergone more than two-thirds of the 342 flight hours needed for certification, but further flights were held up until testing resumed in mid-May.
The 410kN engine is scheduled to receive certification in May 1996 and enter service on the first "B"-market 777-200 for British Airways in December 1996, de-rated to 400kN.
Source: Flight International
