WASHINGTON —The Air Force's UH-1N Huey helicopter replacement program has hit a snag: None of the potential offerors meet the threshold requirements with off-the-shelf rotorcraft, necessitating that companies make changes to their aircraft before bidding.

Because of this, the Air Force is pushing back several key dates, the service announced Thursday in a statement. Instead of releasing its final request for proposals (RFP) this month, the service will issue a second draft in April, with the final version coming in summer.

The Air Force aims to keep the other key dates stable, including a planned contract award in fiscal year 2018 and first helicopter delivery in the fiscal 2020-2021 timeframe, according to the statement. It intends to buy 84 UH-1N replacements to defend nuclear missile facilities.  

The original draft RFP, which was issued in December, called for an armored helicopter that could carry nine combat-loaded troops as well as weapons. The aircraft should be able to hit a 135 knot cruise speed and fly at least three hours — and a minimum distance of 225 nautical miles — without needing to be refueled.

The problem, according to the Air Force, is that offerors have identified that existing platforms do not meet 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 (NDI)," the service's statement reads. "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."

The service did not specify which requirements are posing a problem for companies, and that information would be considered unreleasable to the public, said Air Force spokesman Capt. Michael Hertzog.

However, it appears that some off-the-shelf helicopters are closer than others to meeting requirements.

"The scope of required NDI integration varies between the interested offerors," Hertzog said in response to emailed questions from Defense News.