The U.S. Air Force plans to issue a request for proposals in June or July to extend the service life of hundreds of F-16 fighters, the service announced last week.

The Air Force said it wants to extend the structural service life of up to 841 F-16C/D Block 40/42 and 50/52 aircraft to 13,856 equivalent flight hours, up from 8,000, according to a June 12 notice in FedBizOpps.

“The F-16 structural service life extension program (SLEP) is intended to be a depot-level upgrade program to replace or re-work known life-limited structure to preclude the onset of widespread fatigue damage, maintain safety of flight and enhance aircraft availability,” the Air Force wrote in its fiscal year 2018 budget request.

The Air Force intends to award a contract worth up to $403 million in May 2018. The notice describes the contract as a small-business set-aside.