The Air Force released Feb. 28 a draft request for proposals for the Open Skies Treat Aircraft Recapitalization (OSTAR) program to replace the Pentagon’s aging OC-135B observation aircraft.

The service plans to field two new aircraft to replace the Boeing [BA]-built modified WC-135 Constant Phoenix, which have been in service since the early 1990s and operate under the Open Skies Treaty. A final request for proposals (RFP) is expected in May, with responses due 45 days after its release.

An OC-135B Observation Aircraft from the 45th Reconnaissance Squadron, at Offutt AFB, Neb., sits on the flight line Jan. 16 at Wright-Patterson AFB, Ohio. (Photo: Air Force)

Contract award is expected by the end of February 2020, and will include a base period of five years with an option of five additional years, according to the draft RFP, posted Thursday on FedBizOpps. The OSTAR program will be awarded via an indefinite-delivery/indefinite-quantity contract, with a maximum award amount of $648 million.

The fiscal year 2019 defense appropriations bill signed by Congress in September 2018 included over $146 million in Air Force research, development, test and evaluation funds for the OC-135B recap program, including $125 million to procure the first aircraft and over $21 million for mission equipment integration.

The Air Force originally had three OC-135B aircraft performing unarmed observation flights over Open Skies Treaty nations, but only two remain. Those aircraft were built over 50 years ago and have begun to break down during deployments, service officials said in September 2018 at the service’s Life Cycle Industry Day conference in Dayton, Ohio (Defense Daily, Sept. 13, 2018).