The US Air Force has finally issued an official request for proposals for a program to manufacture new wings for its aging A-10 Thunderbolt attack aircraft. The deadline for proposals from would-be contractors is August 23. But the program will likely not be started before some of the Air Force's older A-10s have to be grounded, as a previous wing-replacement program (awarded to Boeing) has reached its end.

The program, called the A-10 Thunderbolt Advanced Continuation Kit (abbreviated as ATTACK), builds upon the previous Wing Replacement Program, which upgraded 173 A-10 aircraft between 2007 and 2016. ATTACK will deliver a maximum of 112 pairs of wings and associated parts over a five-year ordering period, following an initial delivery of three wing sets to verify quality of work. The Air Force will install the new wings at its A-10 depot at the Ogden Air Logistics Center in Utah.

The statement of work will require whoever wins the contract to develop their own 3D models of the wing sets, flaps, and other parts from the Air Force's specifications. This may give Boeing a slight edge, since the company has already done most of this work and has demonstrated an ability to deliver the wings. But it's not clear yet if Boeing will bid on the new program, which is slightly smaller and shorter in duration than the original re-wing program.

The A-10—originally manufactured by Fairchild Republic Co., now part of Northrop Grumman—has been the Air Force's primary close air support (CAS) aircraft for more than 40 years. Originally intended for the role of taking on the waves of Soviet armored vehicles expected to roll through the Fulda Gap in a European war, the A-10 was designed to fly low and slow—and keep flying despite damage from ground fire.

Air Force officials have said that the CAS role will eventually be taken up by the F-35A Lightning II Joint Strike Fighter. But delivery of the F-35A has lagged. And the service's leadership relented on efforts to retire the A-10 completely because the new stealthy fighter is not yet ready for the CAS mission. Also, no other aircraft currently in the Air Force's inventory can provide the capabilities that the A-10 has served up in the ongoing wars in Afghanistan and Syria (though the B-52 has been used with some regularity in the CAS role in Afghanistan, as have the AC-130 and to a lesser degree, the B-1B ).

While the Air Force is now moving forward with the procurement for new wings, some of the 112 aircraft slated to benefit from the upgrade program will likely have to be pulled from service long before the first wing sets are delivered. And the F-35 is not expected to enter full-scale production until 2019. So even as the five-step, five-year procurement of wings goes forward, the Air Force will likely have to ground as much as a third of the A-10 fleet by the end of 2018—putting even more demand on the planes that remain in service as conflicts in Syria and Afghanistan show no end in sight.

And it's not even certain if the program will ever get fully airborne. Right now, the Air Force only has the funding for the low-rate initial production of wings, and the delivery time frame for those wings is not yet set.