The C-17 entered service ten years ago, and those first few aircraft quickly compiled 3,000 flight hours supporting peacekeeping operations in Bosnia. Each C-17 has a useful life of 30,000 flight hours, but the current force is flying such long, and hard (landing on rough fields) flights that many of the early model C-17s will be worn out within five or so years. This attrition is accelerated by the fact that the early model C-17s are structurally different, and weaker, than the later model C-17s. The wing box in the center of the fuselage was insufficiently strong for the loads placed on it. This was corrected later in the production run, but those early planes are going to wear out faster than later model planes of the same flight hours. Adding to this problem is the fact that many C-17s are landing on rough fields with heavy loads and are taking life time shortening structural damage. We have flown a lot of C-17s into northern Iraq, Afghanistan, Pakistan and a bunch of other stans with rough/short strips in 2001 and 2003. The C-17 was built for this sort of thing, but lots of these landing come at the price of shorter useful life.
Its always been an uphill fight getting new air transports built. There were so many delays in the C-17 program that, when the 1991 Gulf War came along, the C-17 was not available and the the C-141 transports, that was supposed to keep flying until 2010, were basically worn out and had to be retired early. Now the C-17s are doing more work, to make up for the missing C-141s. Originally, there were to be 120 C-17s (at $135 million each), with production ending in 2004. After September 11, 2001, it was realized that more air transports would be needed, and the production run of the C-17 was increased to 180. It is now proposed to increase it again to 222 aircraft. But logistics planners insist that 300 will be needed, if wartime needs are to be met. Moreover, the rapid deterioration of the early model C-17s means that eventually 350, or more, will have to be built to maintain a fleet of 300 transports.
The major problem is that the air force is run by combat pilots. Although they recognize the importance of the C-17, they tend to focus on getting warplanes built. Additional C-17 construction comes at the expense of building new combat aircraft, and thats a hard sell inside the air force. Usually, it lobbying by the army, and other branches of the government, that compels Congress to strong arm the air force generals to build the needed C-17s. Its an ugly, messy and time consuming way to get aircraft built, but it works.
The U.S. Air Force is desperately scrambling to get money to build its new F-22 and F-35 fighters. But in the meantime, an even more essential aircraft, the new C-17 transport, is being worked to death. The problem is that the C-17 is more in demand during the war on terror than are air force combat aircraft. Only the two dozen AC-130 gunships, and a hundred or so A-10 ground attack aircraft and F-16 fighter-bombers are getting steady work these days. But their workload is nothing compared to the C-17s, which are in constant demand to deliver personnel and material to American troops in Iraq, Afghanistan, and many other places where the war on terror is being fought.