Boeing's 777 full-scale fatigue-test airframe had undergone 120,000 simulated flights between January 1995 and 13 March this year, representing double the aircraft's 30-year design service objective, and making this the most extensive fatigue test to be carried out by the company.

Boeing structural engineers are "very pleased" with the results of the tests. "We got some cracking in the current tests," says structures senior manager Jack Winchester, "but we kept a running comparison against the 767 at the same relative point in time and it was 30-40% less." No significant cracking was discovered, and the small "issues" are "spread around", says Winchester.

The airframe will now be thoroughly inspected and used to validate Boeing's in-service structural-inspection plan, which was agreed with airlines and regulatory agencies. "Then we'll do a tear-down inspection, where we will remove a few fasteners from a portion of the airframe in areas that we know historically have been subject to some level of fatigue," says Winchester.

The airframe was subjected to repeated "spectrum" loading. Each spectrum has a block of 5,000 flights, with each block made up of five different flight types which vary in severity and frequency of application.

Source: Flight International