Naval Air: F-18 Fleet Falling Apart

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September 16, 2011: The U.S. Navy is encountering more problems with wear and tear among more than a thousand F-18 aircraft it, and the marines, operate. It was three years ago that the navy found that both their older F-18C Hornet fighters, and their newer F-18E "Super Hornet" were wearing out faster than expected. Years of heavy use in support of the war on terror are bringing forward the time when worn out F-18s will have to be retired. At that point, the aircraft will have too many worn out components for even a heavy refurbishment to cope with.

This was sort of expected with the F-18Cs, which entered service during the late 1970s and early 80s. These aircraft were expected to last about twenty years. But that was based on a peacetime tempo of operations, with about a hundred carrier landings (which is hard on the airframe) per year. There have been more than that because of the 1991 Gulf War (and the subsequent decade of patrolling the no-fly zone) and the war on terror. So to keep enough of these aircraft operational until the F-35 arrives to replace them at the end of the decade, new structural components (mainly the center barrel sections) were manufactured. This was good news for foreign users of the F-18C, who want to keep their aircraft operational for longer.

The F-18E entered service about a decade ago, and was supposed to last 6,000 flight hours. But the portion of the wing that supports the pylons holding stuff (bombs, missiles, equipment pods or extra fuel tanks) is now expected to be good for no more than 3,000 flight hours. The metal, in effect, is weakening faster than expected. Such "metal fatigue", which ultimately results in the metal breaking, is normal for all aircraft. Calculating the life of such parts is still part art, as well as a lot of science. Again, unexpectedly high combat operations are the culprit. One specific reason for the problem was the larger than expected number of carrier landings carrying bombs. That's because so many missions flown over Iraq and Afghanistan did not require F-18Es to use their bombs or missiles.

The navy is modifying existing F-18Es to fix the problem, which is a normal response to such situations. Sometimes these fixes cost millions of dollars per aircraft, but this particular fatigue problem will cost a lot less to fix. The wing metal fatigue problem does not occur with the older F-18s (the A, C and D models) because, while they are also called F-18s, they are not the same as the F-18 E, F and G models. That's because, when the navy decided to build a replacement for the earlier F-18, they found they could get away with calling it an upgraded F-18 model. Thus, instead of it being called the F-24 (the next number available since the start of the Department of Defense's standard designation system in 1962) it could be called the F-18 E and F. While the F-18E looks like the original F-18, it is actually quite different. The F-18E is about 25 percent larger (and heavier) than the earlier F-18s, and had a new type of engine. By calling it an upgrade, it was easier for the navy to get the money from Congress. That's because, in the early 1990s, Congress was expecting a "peace dividend" from the end of the Cold War, and was slashing the defense budget. There was a lot of commonality between the two F-18s, but they are basically two different aircraft. Thus when used more heavily than expected, they developed metal fatigue in different parts of the airframe.

The refurbishment of the F-18Es will extend their useful life to 10,000 flight hours, up from the original 8,600. Dozens of F-18Es have passed the 3,000 hour mark. The F-18As are good for about the same number of hours, and some have already reached 8,500 hours. With F-18s flying (on average) 330 hours a year, the new F-35s will arrive just as many of the older F-18As are retired because of old age. Commanders are being told to try and assign the older F-18s, closest to their fuselage expiration date, to less demanding missions (that don’t require carrying a lot of weight or violent maneuvering.)

 


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