The U.S. Air Force is flying the oldest fleet of aircraft in its history, and wants to replace most of the older planes with new aircraft. But there is also pressure to simply update and refurbish existing aircraft. The B-52 bombers and KC-135 tankers average over 40 years old. The F-15 fleet averages over 18 years old. The F-117 fleet is over 17 years old, and the F-16s average 12 years old. The problem is that many of the oldest aircraft are the most effective and cheapest to operate. The best example of this is the B-52, which is much older than the other heavy bombers in service (B-1 and B-2), but are much cheaper to fly. The air force is having a very hard time making an economic case for replacing the KC-135 tankers. Although these aircraft are old, they dont have that many flight hours on them. In other words, the KC-135s can fly for another decade or more. The transports, like the older C-5s and C-131s, get used a lot more than the bombers and fighters, and wear out much sooner. But the air force would rather buy new warplanes, than replace rickety transports. Congress usually has to compel the air force to buy more, badly needed, transports.

Another problem is upgrades. It has not gone unnoticed that many military aircraft are serving for decades, and kept effective by upgrading key components. But air force fighter pilots believe that the best investment is the development of the most modern new aircraft. This is seen as an outmoded custom. For over half a century, from World War I to the 1960s, it was customary to build new warplanes every 5-10 years. But by the 1970s, the new technology became more expensive, and took much longer to develop. It also became clear that speed and maneuverability were not as critical as they once were. Missiles became more effective, as did radars and electronic warfare equipment. Without much fanfare, the equipment became more important, and lethal, than the aircraft carrying the stuff. Pilot skill is also, as always, a critical element. With more gadgets aboard, pilots required more  training to deal with it all. 

At the same time, there is no major air war, between somewhat equally matched opponents, to demonstrate what really worked better, old school or new style. The wars between Arabs and Israelis, and Indians and Pakistanis, provided some practical experience. But the results were murky. Pilot skill, as always, was paramount. This was often the case even when the more skilled pilots were flying inferior aircraft. This is also nothing new. 

So either out of necessity (lack of money), or on purpose, many nations began keeping older aircraft, and putting new radars, missiles and electronic warfare gear on them. By spending more on training (actually flying the aircraft, and letting the pilots practice), nations could produce truly lethal air forces, even with "old" aircraft. The inability of many nations to afford the latest, and very expensive, aircraft, made upgrades very common. This has led many politicians to begin questioning the wisdom of buying very expensive new aircraft. The main advocates for completely new aircraft, the air force generals who were fighter pilots, are seen as less than balanced in their assessment of the situation. The fighter generals have not had a real war to test their theories, and are seen as flying on autopilot when it comes to deciding how to proceed in procuring future air combat systems. As a result, there is weakening support for buying new fighters like the F-22, Rafael, Eurofighter and whatever top-of-the-line stuff the Russians are offering.