The Navy has grounded one-fifth of its A6E attack aircraft because tests have shown that the plane's wings may last only half as long as believed, Navy officials said yesterday.
The Navy has grounded 64 A6Es and has restricted the maneuvers of another 112, affecting about one-half of the 344-plane fleet. In addition, 11 of the Navy's 66 KA6Ds, similar planes that have been modified into in-flight refueling tankers, have been grounded or restricted.
The A6E is the Navy's only all-weather bomber, built to operate from aircraft carriers. Grumman Aerospace Corp. has been building a version of the plane since the early 1960s and the A6E model has been deployed since 1972.
The recently discovered wing-fatigue problem is the latest in a series of difficulties for the Navy's air arm. Last summer the Navy discovered cracks in the tails of its new F18 fighter jets and stopped accepting the planes until earlier this month, when McDonnell Douglas Corp. completed an improvement program.
The Navy and Grumman said that there have been no accidents because of A6E wing fatigue and that the new restrictions are precautionary. But the Navy also said that it now believes that the wings on the A6E will last between 2,000 and 3,000 flying hours, not 4,400 hours as previously believed.
"Metal fatigue is a function of stress," one Navy officer explained. "The wings get tired and you have to replace them. They don't necessarily fall off. That would certainly be an extreme example."
It costs about $2.5 million and takes about six months to outfit an A6E with a new pair of wings, according to Grumman and Navy officials. If the rewinging is performed as part of a regularly scheduled overhaul, it adds about two months to the rework.
Navy officials said yesterday that they have not determined who should pay for the accelerated rewinging that will be needed, but Grumman spokesman Joe Vranich said the Navy should bear the costs. He said the grounded A6Es already have lasted longer than his New York-based company originally warranted.
Lt. Peter A. Johnstone, a Navy spokesman, said the problem surfaced because of a new and more sophisticated method of analyzing wing stress developed by Grumman. He said the Navy also has been exceeding its original expectations for "wing loading" on the A6Es, meaning that the planes have been loaded with more and heavier missiles and fuel tanks for more hours than originally estimated.
Navy officers said they do not believe that the problem will affect carrier operations around the world, at least in the short run. Only 24 of the 176 planes affected so far are deployed on carriers, probably because the Navy deploys its newest planes and keeps the older ones home as much as possible, they said.
The flight restrictions prevent pilots from putting the planes through certain sharp turns and other maneuvers that stress the wings. The limits are not strict enough to keep planes from landing on carriers, even though the arresting gear used to stop planes on carrier decks sends a jolt through a plane's structure.
The Navy said it has about 30 wings in stock or on order, which "should meet the most immediate requirements."
"Long-term prognosis is under study," the Navy said.
Rewinging could be performed by Grumman, at Navy-owned maintenance facilities or at other contractor-operated rework sites. Navy officials said they probably will use a combination of facilities because of the problem's pressing nature.
"Obviously, the Navy is our most important customer, and we're going to do whatever we can to help them out," Vranich said. "But they do have other options."
A Navy official said other types of planes probably will be subjected to the new computer-assisted stress tests. Aircraft carriers usually carry a mix of bombers, such as the A6 and A7, and fighter jets, such as the F4 and F14. The new F18 is supposed to attack ground targets and fight enemy planes.