Some time in the next several weeks or months, the Lockheed Martin F-35 programme will pass a historic milestone. The system development and demonstration phase that began 17 years ago appears poised – barring any unforeseen showstoppers – to conclude by the end of summer. The aircraft, engine, simulators and logistics system will shift from development to operational status, albeit six years behind schedule.

As remarks on 28 February by Vice Adm Mat Winter make clear, the Joint Strike Fighter (JSF) still faces perhaps its most important test, which, if surmounted, will secure the programme’s future for decades to come.

The F-35’s capabilities are no longer up for debate. The aircraft’s unique blend of advanced active and passive sensors bring an unprecedented level of situational awareness of the air and surface domains into the cockpit. Taken together with a stealthy radar profile and a potent weapons package, the fighter represents a new approach to air power.

All that means nothing, however, if the F-35 is unaffordable to buy and operate in the quantities planned by the US military. According to Winter, the JSF’s programme executive officer, the aircraft’s costs are unsustainable as the fleet grows.

Such a statement has severe repercussions: the US military expects to increase the fleet from 280 aircraft today to more than 800 over the next five years. If it cannot afford the bill to operate the F-35 in 2022, the Pentagon could be forced to slow procurement. As the production ramp-up slows, planned manufacturing efficiencies will be lost, further increasing costs. It is the familiar “death spiral” of defence acquisition, in which unaffordability leads to lower production volumes, causing costs to rise still further.

Winter’s office is now attempting to intervene. Its strategy covers a broad set of targets. Nearly 200 F-35s delivered before the ninth lot of low-rate initial production must be upgraded to the latest software standard. Lockheed must resolve issues with its maintenance alerting system, and the US government is helping industry fix a chronic and costly spare parts shortage.

Evidence suggests the F-35’s cost problem can be mended. Lockheed’s once-broken final assembly process for the F-35 delivered 66 aircraft last year, exactly on target. The reliability of JSFs delivered last year is markedly better than the jets shipped the year before.

The only question that remains is whether Winter’s cost-reduction strategy will be too little and too late.