The US Congressional Budget Office (CBO) reports that both availability rates and flying hours have declined for the US Air Force (USAF) and Department of the Navy (DoN) over the last two decades.

From 2000-2020, availability rates for all aircraft across both the USAF and DoN (which includes the US Navy and US Marine Corps) fell from around 60% to the 40-50% range, says the CBO. The decline in DoN availability rates was more pronounced, hitting just 40% in 2019.


Source: US Air Force

Mechanics tow a stripped-down F-15C at Robins AFB, Georgia in November 2021

Flying hours per aircraft have also fallen over the last two decades, with a sharper decline during the coronavirus pandemic in 2020. DoN flying hours declined from around 350h per aircraft per year to around 300h, while USAF flying hours fell from just under 300h annually to 250h.

“The trends for fighters and attack aircraft in each service mirror the trends observed for the services’ fleets as a whole,” says the CBO. “Of particular note is the steep decline in the availability rate for DoN fighters and attack aircraft, which drives the decline in the availability rate of the total fleet.”

For the DoN, the CBO looked at fighter types such as the Boeing AV-8B, Northrop Grumman EA-6B, Boeing EA-18G and F/A-18, and the Grumman F-14. USAF types included the Fairchild-Republic A-10, Boeing F-15, Lockheed Martin F-16, and F-22. The Lockheed F-35 was not analysed because the data sets the CBO used did not accurately reflect the type’s availability.

“Since 2012, the availability rates of DoN fighters and attack aircraft have fallen well below the air force’s rates,” says the CBO.

“The rates for both services have been lower than they were in the early 2000s. DoN fighters and attack aircraft have consistently flown more hours per aircraft than have the air force’s fighters and attack aircraft. Both services have experienced declines in flying hours per aircraft.”

The DoN’s numbers were particularly affected by the F/A-18 C/D, a type retired by the navy, but still in service with the Marines. Delays in high flight-hour inspections, which also include actions to extend the type’s operating life, affected its availability over the survey period.

“Both the air force and DoN operate helicopters and tiltrotor aircraft,” adds the CBO. “However, helicopters and tiltrotor aircraft make up a much larger fraction of DoN’s fleet, representing 34% of its total fleet compared with just 3% of the air force’s fleet. The trends for those aircraft are consistent with fleetwide trends in both services.”

The CBO adds that it used a somewhat stricter measure to assess “availability” than that used by the US Department of Defense (DoD). The CBO’s measure looks at all aircraft, including those in storage or receiving depot level maintenance, while the DoD measures only the availability of aircraft with operating units.

In 2019, for example, the DoD deemed its availability rate for the F-15C at 67%, while the CBO set it at 40%.