The US Army has launched a long-awaited search for an improved engine design for nearly 3,000 medium-twin helicopters, with potentially a surprise bidder waiting in the wings.

For nearly a decade, the competition to build the successor of the GE Aviation T700 shaped up as a head-to-head battle. Incumbent GE Aviation offered the single-spool GE3000 against a challenge from the dual-spool HPW3000, which is being developed by a Honeywell/Pratt & Whitney (P&W) joint venture named ATEC..

Both firms have each developed and tested two prototype engines and new inlet particle separators under an army-funded technology maturation programme called advanced affordable turbine engine (AATE).

But at least one more bidder could join the next phase of the competition, in which the army will award contracts for up to two firms to produce a preliminary design of the improved turbine engine known as ITEP.

“We fully expect other engine vendors that didn’t participate in AATE to come to participate in this programme as well,” says Lt Col Curt Kuetemeyer, the army’s ITEP product manager. “We feel confident that they can mature the specific technologies we have for production.”

The army is demanding a lot for the ITEP. The goal is to increase the power output over the T700 by nearly half while reducing the specific fuel consumption by one quarter. The entire package must fit inside the existing dimensions of T700 engine installed on more than 2,100 Sikorsky UH-60 Blackhawks and nearly 700 Boeing AH-64E Apache Longbows.

Only two other engine manufacturers are obvious candidates to participate in ITEP, and one – Rolls-Royce – confirms to Flightglobal that it has no plans to join the competition. That leaves only Turbomeca, which supplies the RTM322 engine for the UK’s AH-64 fleet. Turbomeca did not respond to a request for comment.

The army plans to award up to two contracts before end of Fiscal 2016. The winning bidders will have 24 months to produce preliminary designs for the ITEP engine. At that point, the army plans to downselect to a single bidder for a six-year engineering and development phase.

The programme is funded strictly as a re-engining programme for Black Hawks and Apaches. Depending on how requirements are set for the army’s high-speed future vertical lift (FVL), the ITEP engine could serve has the propulsion for the light and medium versions.

But the ITEP is dedicated to support the army’s strategy of modernising its current fleet while developing a high-speed replacement under FVL.