The US Air Force has delayed the release of its final request for proposal to recapitalise its fleet of UH-1N Huey helicopters, after contractors told the service their off-the-shelf solutions would not meet all of the proposed requirements.

The USAF had slated the final RFP for this month, but has pushed its release to this summer. The service also delayed the release of its second draft RFP to April 2017, according to a 16 February USAF statement. The service still plans to award a contract in fiscal 2018 that would deliver the first operational helicopter in fiscal 2020.

In December, the USAF released its initial draft RFP to replace its Vietnam-era Bell UH-1N Hueys, calling for a full and open competition to procure up to 84 helicopters. But following the release of the draft RFP, contractors told the air force that commercially available aircraft would not meet all of the service’s threshold requirements.

“Consequently, the air force is shifting the acquisition approach to a pre-Milestone C entry to allow for integration of non-developmental items,” the USAF states. “This will allow interested offerors an opportunity to integrate NDI into their off-the-shelf platform to meet all requirements for the UH-1N replacement.”

Helicopter manufacturers have already voiced their concern that the current requirements for the Huey recapitalisation essentially create a sole-source competition that would award Sikorksy, which makes the UH-60 Black Hawk. Earlier iterations of the contract considered a sole-source buy of UH-60M Black Hawks, but the service decided to move ahead with a full and open competition.

The air force has called for the replacement helicopter to be able to carry at least nine combat troops plus equipment at a speed of at least 135kt (250km/h). In September, the USAF’s acquisition chief clarified that the replacement Hueys would not be required to carry more than nine troops.