January31, 2007: The U.S. Air Force is still looking for aircraft to replace over 500 aging ( 40 years old, or older) KC-135 tankers. At the moment, there are three prime candidates. The leading one is the KC-767, which is already been selected by Italy and Japan. This aircraft is based on the Boeing 767-200 airliner, which sells for about $120 million. Boeing developed the KC-767, at a cost of nearly a billion dollars, on its own. Boeing also developed the original KC-135 tanker in the 1950s. All 732 KC-135s were built between 1956 and 1965.

Over the decades, the KC-135 fleet has undergone constant repair and reconstruction. New engines, and new structural components have been added, as older items wore out, or showed signs of wearing out. Currently, some 40 percent of the KC-135s are out of action for maintenance problems. In theory, an aircraft can be continually rebuilt and kept in flying condition. But the air force, and some commercial air lines, are finding that the maintenance problems multiply and become unpredictable as the aircraft get older and, after a while, the downtime for maintenance is more trouble than it's worth. For example, the hundred oldest KC-135s spend an average of 80 days a year undergoing major repairs. However, when you do the math, you find that overhauling and maintaining the current KC-135 fleet would be about $10 billion cheaper than buying new 767s. There is risk in keeping 40 year old aircraft flying, but the safety record of the KC-135 remains excellent. Newer isn't always better, but it is often more expensive.

The four engine KC-135 carries 90 tons of fuel and can transfer up to 68 tons. Consider that a B-52 carries over 140 tons of jet fuel, an F-15, over five tons. A KC-767 carries about as much fuel as the KC-135. The European firm Airbus, is offering the KC-30, based on the Airbus 330-300, which normally sells for $160 million each. The KC-30 carries 20 percent more fuel than the KC-767, and more cargo pallets (26 versus 19).

The KC-135 has long made itself useful carrying cargo and passengers, as well as fuel, and both the KC-767 and KC-30 have more capacity for this. Another option is a tanker based on the larger Boeing 777-200LR, which sells for about $230 million each. This KC-777 would have 65 percent more fuel capacity than the KC-767, and 95 percent more cargo capacity. Bigger is sometimes better if you're a flying gas station. The KC-767 was developed partly because it is about the same size as the KC-135 (wingspan is 156 feet, ten more than the KC-135). The wingspan of the KC-777 would be 213 feet. Moreover, it would take about three years to develop the KC-777, while the KC-767 is ready to go now, and the KC-30 will enter service with Australia next year. Using the KC-777 would reduce the number of tankers needed from 179 to 120, or less, and be cheaper in the long run. So many choices, and no one in authority is, as yet, willing to make a decision on this.