The chair of the US Senate Appropriations committee has approved the chamber’s version of the fiscal year 2018 defence spending bill this week, a move that pushes the legislation closer to final passage.

In June, the US House of Representatives Appropriations committee approved their version of the FY2018 defense appropriations bill. The Senate appropriations bill adds fewer Lockheed Martin F-35s to the budget than the Administration requested compared to the House version of the bill.

The House proposed adding 14 more Lockheed Martin F-35s above the president’s original budget proposal. The Senate mark calls for $1 billion to fund eight additional F-35s, including four F-35Cs and four F-35Bs.

Despite a lower initial F-35 procurement, the Senate bill still provides an additional $120 million to fund a planned increase of F-35 procurement in FY2019, as well as $750 million to fund spares and repair parts to address maintenance and readiness issues across the joint force.

The maintenance funding boost comes on the heels of a recent Government Accountability Office report which stated F-35s could not fly 22% of the time between January and August in 2017 due to spare parts shortages.

Still, the simultaneous increase in maintenance and procurement does not jibe with another section of the same report which warned that long after Lockheed completes its deliveries, the F-35 programme will continue to face sustainment issues since the Pentagon has failed to identify all the technical data needed from the prime contractor to ensure weapons system performance and support.

Both chambers agreed on other line items, including for the Boeing F/A-18E/F Super Hornet. The Senate proposed adding $739 million for 10 more Boeing F/A-18E/Fs. The Senate also called for adding $108 million for eight Sikorsky UH-60 Black Hawk helicopters for the Army National Guard, the same level as the House version.

Both appropriations bills include provisions to support a next-generation Joint Surveillance Target Attack Radar System aircraft, a recapitalisation that has remained a sacred cow for lawmakers even as the air force has positioned the programme on its chopping block.