Start with what is being counted
The number of aircraft an organization owns does not answer how much of the time they are available for assigned work. GAO's October 2024 tactical-aircraft review defines a mission capable rate in terms of the share of time an aircraft can fly and perform at least one mission. That makes it a measure of availability under a defined rule, rather than simply a count of working airframes.
The distinction is easier to see with an imaginary vehicle. It might be available for one task while equipment required for another is awaiting repair. Under a rule that requires at least one assigned task, that condition can be counted differently from a rule requiring every task. The arithmetic can be correct in both reports while the percentages answer different questions.
One fleet can have several valid rates
GAO's June 2026 F-35 sustainment report illustrates this directly. For fiscal year 2025, it reported a 44 percent mission capable rate and a 25 percent full mission capable rate across the fleet. The latter requires the ability to perform all assigned missions. The report also states that these rates assess aircraft in the possession of units. That scope belongs with the numbers.
These are historical annual measures in the cited audit. They are not a live count of aircraft ready at a specific base today. Nor can the difference between the two percentages be interpreted as the percentage of aircraft permanently unusable. For readers, a careful comparison preserves the reporting period, population and definition before drawing a conclusion about a trend.
Maintenance makes availability a system question
GAO's 2024 review points to interconnected contributors including aging equipment, maintenance challenges and supply support. Its 2026 F-35 review also identifies spare-parts constraints and dependence on contractors among sustainment challenges. The broader implication is that availability emerges from the aircraft and the organization supporting it. A performance specification alone cannot describe that relationship.
Our editorial practice is to place a percentage beside its definition, date range and source. We would look for an explanation of changes before ranking unlike fleets, and for evidence of outcomes before treating additional maintenance spending as an improvement. A repair initiative may be sensible while its effect remains unmeasured. Following that effect over successive reports gives readers a more useful account than alternating between an impressive aircraft specification and an alarming readiness headline.
The 44 percent and 25 percent figures are GAO's reported fiscal-year-2025 fleet measures, published June 2026. The source definitions restrict the population to aircraft in units' possession. This article makes no assessment of current local availability, future readiness or any B-21 metric.
Read the evidence.
- 01Tactical Aircraft: Operation and Maintenance Spending Varies by System, and Availability Generally Does Not Meet Service GoalsUS Government Accountability Office · 21 Oct 2024
- 02F-35 Sustainment: Actions Needed to Ensure Updated Strategy Improves Persistent Readiness ChallengesUS Government Accountability Office · 11 Jun 2026