The delays in the production of the F-35 are forcing the USAF to extend the service life of hundreds of aging F-16 aircraft:
The U.S. Air Force will refurbish several hundred of its 22 ton F-16 fighters, because their replacement, the 31 ton F-35 is not arriving in time. The F-35 began development in the 1990s and was supposed to enter service in 2011. That has since slipped to 2017, or the end of the decade, depending on who you believe. Whichever date proves accurate, the air force has a problem. Its F-16s are old, and by 2016 many will be too old to operate. The average age of existing F-16s is over 20 years, and the average aircraft has over 5,000 flight hours on it. Two years ago, the first Block 40 F-16 passed 7,000 hours. Three years ago, the first of the earliest models (a Block 25) F-16 passed 7,000 hours.
Depending on how late the F-35 is, the air force will refurbish 300-600 Block 40 and 50 aircraft. The work will concentrate on extending the life of the airframe, plus some electronics upgrades. The air force does this sort of thing frequently to all aircraft models. It’s called SLEP (Service Life Extension Program), and this one is special only because it concentrates on very old aircraft and is intended to keep these birds viable for another 5-10 years.
The F-16C was originally designed for a service life of 4,000 hours in the air. But advances in engineering, materials and maintenance techniques have extended that to over 8,000 hours. Because of the wars in Iraq and Afghanistan, F-16s sent to these areas will fly over a thousand hours a year more than what they would fly in peacetime. The current planned SLEP will extend F-16C flight hours to 10,000 (10K) or more.
