Effects of Large-Scale Maintenance Actions on the Availability of the Air Force's Aircraft [open pdf - 3MB]
From the At a Glance: "The Department of Defense often confronts decisions about whether to repair a piece of equipment (such as a ship, vehicle, or aircraft) to extend its service life or whether to replace it with a new piece of equipment. One important consideration is whether large-scale maintenance--such as an engine replacement or structural upgrade--would make the equipment more available for training or combat. As equipment ages, more parts tend to break, so the equipment tends to become less available. Large-scale maintenance might sometimes slow or reverse that decline. This report examines the availability of six Air Force aircraft fleets after large-scale maintenance that has occurred since the mid-1990s. Although most aircraft periodically undergo heavy maintenance during their lifetime, the Congressional Budget Office focused on modifications that changed the aircrafts' Mission Design Series designation. Those types of changes usually focus on improving an aircraft's performance and reliability so as to keep it in the force for an extended time."
Congressional Budget Office: http://www.cbo.gov/