The Government Accountability Office released GAO-26-108113 on June 11, 2026, delivering a stark assessment of the F-35 program's sustainment trajectory. The report, titled F-35 Sustainment: Actions Needed to Ensure Updated Strategy Improves Persistent Readiness Challenges, documented a four-year freefall in aircraft availability: the fleet's full mission capable (FMC) rate dropped from 38.1% in FY2021 to just 24.6% in FY2025. The overall mission-capable (MC) rate — encompassing jets cleared for at least some missions — fell from 66.8% to 44.1% over the same period. Both figures represent significant deterioration for a program that is the cornerstone of U.S. tactical aviation modernization and accounts for the largest single acquisition in Pentagon history.

Variant-by-Variant Breakdown

The readiness crisis is not uniform across the joint strike fighter family. The Air Force's F-35A, the conventional takeoff-and-landing variant fielded in the largest numbers, posted an FMC rate of 28.5% — well below any reasonable operational benchmark, but still the strongest performer of the three variants. The Marine Corps' F-35B, designed for short takeoff and vertical landing operations, sits at roughly 14% FMC. The Navy's carrier-based F-35C is the lowest-performing variant, with an FMC rate roughly on par with the F-35B — both running at approximately half the F-35A rate. The F-35C figure is particularly consequential given its central role in carrier air wing strike packages and the Navy's long-range kill chain. Taken together, these numbers mean the average Navy or Marine Corps squadron is operating with a small fraction of its aircraft available for the full spectrum of assigned missions at any given time — a readiness posture that would have triggered a formal review in any prior generation of tactical fighter programs.

GAO identified three primary causes driving readiness degradation across all variants. The first is the TR-3 software upgrade, whose shortcomings have limited newly delivered aircraft to basic training missions only, preventing fresh jets from expanding operational capacity and adding utilization stress to older airframes that are already being stretched. The second cause is spare parts shortages, which have constrained maintenance throughput at depots and organizational-level shops alike. The third is corrosion, a persistent structural problem that affects all three variants and generates sustained demand for specialized depot work. The interaction of these three failure modes — software problems grounding new jets, parts shortages slowing depot and field-level repairs, and corrosion degrading the airframes that do manage to get airborne — explains the compounding decline in both FMC and MC rates across the four fiscal years the GAO reviewed.

What It Means for Contractors

The Pentagon's formal response to the readiness crisis is the "Global Support Solution (GSS) Reset," a comprehensive revised sustainment strategy intended to stabilize availability rates and bring cost growth under control. GAO determined the GSS Reset will require $13.7 billion more than previously planned through FY2031 — a figure that reflects the scale of the sustainment deficit accumulated over years of underinvestment in parts inventory, depot capacity, and software stability. Even with that additional commitment secured, GAO projects that annual sustainment costs will still exceed individual service affordability targets by more than $1 billion per year by the mid-2030s. That structural cost overage, persisting even after a $13.7 billion top-up, is a direct signal that program offices will face sustained pressure to renegotiate contracts, restructure delivery schedules, and extract measurable cost reductions from every tier of the supply chain well into the next decade.

For parts suppliers and depot operators, the GAO report frames a specific and quantified constraint: industry capacity limitations threaten the delivery of over $7 billion in additional parts required to execute the GSS Reset on schedule. That number represents the gap between what the sustainment strategy demands and what the current industrial base can physically produce and deliver. Lockheed Martin has committed $2 billion in advanced spare parts funding to address near-term shortfalls, but $2 billion against a $7 billion delivery risk leaves a substantial exposure that will need to be closed through expanded manufacturing capacity, sub-tier development, or both.

GAO issued three formal recommendations directed at the Department of Defense. First, DoD should develop proactive risk-mitigation plans specifically tied to GSS Reset initiatives, rather than reacting to slippage after the fact. Second, the Department should redesign its incentive approaches for the prime contractor to include financial penalties or revised performance thresholds that create meaningful accountability for readiness outcomes. Third, the Joint Program Office should implement quality controls for documenting how incentive metrics are tracked, measured, and reported — closing a gap that GAO found allowed performance data to go undocumented in ways that obscured accountability. DoD concurred with all three recommendations, and the Joint Program Office stated publicly that it "concurs with the GAO's findings." Full concurrence across the board means implementation timelines will be set, and contractors with performance-based logistics agreements or availability-based contracts should anticipate renegotiation pressure centered on those revised thresholds and penalties.

The readiness gap also creates near-term opportunity for suppliers positioned to close it. Depot-level maintenance providers with corrosion-control specialization, spare parts manufacturers who can credibly demonstrate production surge capability, and software integration firms with TR-3 clearances are each directly relevant to the three root causes GAO identified. Companies that can make a quantified case for accelerating depot throughput or increasing parts yield will be in the strongest competitive position as the services begin executing GSS Reset task orders. The $7 billion parts delivery risk identified by GAO is, from the supplier side, a $7 billion market opening for firms that can prove they can deliver at scale and on schedule. The incentive structure changes coming out of GAO's second recommendation — penalties and revised thresholds — will also reshape how future availability contracts are written. Contractors who build robust internal metrics tracking and documentation systems now, ahead of those contract changes, will enter negotiations with a credibility advantage over firms that wait for the new requirements to arrive before adapting.

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