The U.S. Air Force has about 5,600 aircraft, which range in age from just-delivered to 60 years old. Many of those aircraft—including the costly-to-replace F-16C/D and F-15C/D fighters, F-15E multirole fighters, C-130 cargo aircraft, and B-1B bombers—are nearing the end of their service life. In this report, CBO estimates the cost of replacing those aircraft.
Replacement Costs. CBO projects that replacing the aircraft in the current fleet (essentially one-for-one) would cost an average of $15 billion a year in the 2020s. That figure would rise to $23 billion in the 2030s and then fall back to $15 billion in the 2040s. In comparison, appropriations for procuring new aircraft averaged about $12 billion per year between 1980 and 2017. (All amounts are in 2018 dollars.)
Methods. The projections are based on publicly articulated procurement plans for some aircraft and, for aircraft without such plans, on their typical retirement age; the projections do not take into account the costs of development, operations and maintenance, modifications, or personnel associated with aircraft.
Uncertainty. Replacement costs would be lower if the Air Force decided to extend the service life of some aircraft or if the costs of procuring some aircraft were lower than CBO projects. Replacement costs would be higher if the opposite occurred.
The Study is here — https://www.cbo.gov/system/files?file=2018-12/54657-AirForceAviationFunding.pdf