Sikorsky has introduced the first HH-60W combat rescue helicopter (CRH) into final assembly ahead of a scheduled first flight by the end of this year.

The derivative of the UH-60M is the first of a planned 112-aircraft production programme worth $8.12 billion to replace the aging fleet charged with rescuing downed US Air Force pilots.

The start of final assembly means the HH-60W is two months ahead of schedule in manufacturing, says Tim Healy, director of Sikorsky Air Force Programmes.

The programme remains ahead of schedule despite repeated concerns from government auditors that the air force is ignoring “best practices” to rush the long-awaited HH-60G replacement into service.

The Air Force launched the CRH programme in 2014 as a minor derivative of an existing platform only after several attempts to buy a larger helicopter failed to overcome a series of legal challenges by losing bidders.

Instead of buying a much larger platform for the mission, the Air Force is modifying the UH-60M with the tactical mission kit (TMK), which integrators new sensors, radar and multiple self-defence systems.

Sikorsky’s workers also will install a new fuel system in final assembly to raises internal fuel to 660gal, or twice the internal fuel tank capacity of a UH-60M.

Sikorsky, a Lockheed Martin-owned company, plans to build nine engineering and manufacturing development aircraft, along with 103 HH-60Ws for the Air Force programme.