Boeing will decide in the next few weeks whether further fatigue testing of its 777 is required, before "tearing down" the full-scale fatigue specimen for analysis, but it is already applying test results to aircraft manufacture.

Planned tests simulating 120,000 flight cycles ended in March. Boeing says that the number of design changes arising from these tests will be close to, or even fewer than, those needed on the 767 and 757.

Michael O'Grady, supervisor of empennage and flight-control surfaces in 777 structures engineering, says that "-a teardown inspection of selected critical areas will be done as soon as it is decided that no further testing is necessary. We expect to know in June."

He says that about 20 "-open design issues have emerged and we expect some design changes. Although the total number has yet to be determined, those identified suggest that the flnal number will be in the range [of] or very possibly lower than on the 757 and 767." There were 28 design changes on the 767, and 30 on the 757, arising from 100,000 simulated flight cycles. There had been 121 design changes to the 747, arising from little more than 20,000 test cycles.

Boeing will not wait for a decision on further tests before applying lessons learned from 777 fatigue work. It has already redesigned the landing-gear aft trunnion following the generation of a crack at just over 8,600 cycles.

Source: Flight International