The modernization of the F-35 fighter jet, known as the Block 4 upgrade, has run into major setbacks. A new report has confirmed that this upgrade will not be fully ready until 2031 at the earliest. This marks a five-year delay from the original plan and a two-year slip from the most recent timeline, which targeted 2029.
Expensive Delays in the F-35 Block 4 Upgrade Program
The program has become far more expensive than first expected. What was once estimated to cost $10.6 billion has now grown to $16.5 billion as of 2021, and the figure is still not final. Despite the higher spending, the program will deliver fewer features than originally promised. Out of the planned 66 new capabilities, fewer will make it into the final version. Officials have explained that the exact number of features will only be clear by late 2025.
Some of the more advanced upgrades require new engine and power system improvements. However, these will not be ready in time for the F-35 Block 4 phase and have been pushed further into the future. The latest update shows that the F135 engine core upgrade will not be in production until 2031, meaning other planned capabilities that depend on it will only arrive after 2033.
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Persistent F-35 Production and Delivery Problems
The F-35 program has faced ongoing struggles with delays in production. In 2024, the company delivered all 110 aircraft late, averaging a 238-day delay. This represented a dramatic increase from 2021, when the company delivered only 22 aircraft late with an average delay of just 16 days.
Problems with the Technology Refresh 3 (TR-3) hardware and software caused most of the recent delays. This upgrade is supposed to provide the computing power needed for future improvements, but the rollout has moved slowly.
By May 2024, the company had not delivered 20 F-35 aircraft that were originally scheduled for the previous year. It also faced severe shortages of essential parts. In February 2024, the company reported more than 4,000 missing parts, double the usual average. Of these, more than 1,600 parts were directly tied to TR-3.
The shortages forced the company to remove 52 jets under construction from the production line and place them in storage until the missing components arrived.
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One of the most common problem areas was the wing flap component, which has caused delays for over two years. Engine production has also struggled. In both 2023 and 2024, the F135 engine deliveries were late every single time. On average, the engines were 155 days behind schedule. Although these delays did not stop aircraft from being built, they added further pressure on the already troubled F-35 program.
Criticism has also been raised about the way the contracts are structured. Even though both aircraft and engines were delivered late, the companies involved continued to receive incentive payments worth hundreds of millions of dollars. The system allowed aircraft to be delivered up to 60 days late while still earning partial rewards, which has raised questions about accountability.
Rising Costs and Global Concerns
The financial side of the F-35 program has grown to staggering levels. As of December 2023, the cost of acquiring the jets had reached more than $485 billion. This is nearly 10 percent higher than the 2022 estimate of $442 billion, and more than double the cost that was originally set back in 2001.
When looking at the program’s entire lifetime cost, including maintenance and operations, the figure now exceeds $2 trillion. A large portion of this increase comes from the extra wear on engines caused by the power and cooling demands of the Block 4 upgrades. These issues alone are expected to add $38 billion to the total lifetime cost.
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The ongoing delays and growing costs have raised concerns internationally, not just in the United States. Other countries that rely on the F-35 fighter jet are closely watching these developments. Recommendations have been made to reassess the production capacity and use more modern design tools to avoid further complications.
Even with the mounting challenges, the F-35 remains one of the most widely used advanced fighter jets in the world. It continues to be delivered in large numbers, with between 170 and 190 aircraft expected in 2025. However, the full set of Block 4 improvements, once expected to make the jet even more capable, will now take much longer to arrive and cost billions more than initially planned.