The US Navy is seeking a single-turbine-engined rotorcraft that could achieve an instrument flight rules (IFR) certification: a requirement that could potentially limit the field of candidates in the service’s TH-XX trainer helicopter recapitalisation competition.

The navy will replace its ageing fleet of 113 Bell Helicopter TH-57 Sea Ranger trainers with 105 new aircraft, with production beginning in fiscal year 2020 or 2021, according to a 1 June request for proposals published on the Federal Business Opportunities website.

Use of the term “certifiable” perplexed industry, although the USN clarified in a 22 June notice that if the helicopter does not have a Federal Aviation Administration IFR certification, then it must have the equipment and data to achieve that approval in the future.

“A key component of the navy's acquisition strategy is to focus the evaluation on commercially available aircraft that will meet documented performance and training requirements,” the service says. “One of those requirements is that any replacement rotary training system must be able to operate to the standards set out in Appendix B FAR Part 27.

"The navy is currently working to understand the market and is willing to evaluate aircraft that have the ability to meet current and future FAA FAR Part 27 standards and safely operate within the modern national airspace system.”

Most single-engined helicopters meet visual flight rules (VFR) certification and only one candidate, Leonardo Helicopters' TH-119, a military version of the commercial AgustaWestland AW119Kx, currently meets both the single-engine and IFR-rated requirement. Several other manufacturers are eyeing TH-XX, but it would require significant upgrades to transition their aircraft to an IFR rating under the current regulations.

Controversy is swirling now over changes to the FAA’s regulation Appendix B FAR Part 27, which handles IFR certification for rotorcraft under 3,200kg (7,000lb) carrying nine passengers or under. Industry has criticised the FAA’s approach to rotorcraft safety standards, saying equipment and training for IFR operations in single-engined helicopters is still too expensive.

A 2015 industry association white paper recommended a policy update to Part 27 that would make IFR certification more affordable. The white paper’s supporters include Bell, which is pitching the VFR-certificated 407GXP for the TH-XX programme.

Even if Leonardo’s competitors decide to meet the IFR criteria, it would require significant investment and could put them at a cost disadvantage. Along with the Bell 407GXP and Leonardo’s TH-119, Airbus Helicopters, Boeing and Lockheed Martin are following the competition.

“There are currently no plans for a sole-source replacement of the TH-57,” the USN says. “To date, the navy has not formally evaluated any platform for compliance with current or future FAR Part 27 requirements.”