On Sept. 11, 2007, Boeing announced it had been awarded a 10-year, $1.1 billion U.S. Air Force contract to continue providing programmed depot maintenance for the nation’s KC-135 Stratotanker fleet. Under this contract, more than 200 KC-135 aircraft were to be worked on at facilities in Texas, Oklahoma and Missouri. Since the initial KC-135 PDM contract award in October 1998, Boeing has completed scheduled and unscheduled maintenance on more than 160 aircraft. Conducted every five years, scheduled PDM services include depot-level inspections, repairs, maintenance, modifications, re-painting and supply chain services. Unscheduled maintenance comprises about half of the work performed on each aircraft.