Boeing has started fabrication of the fourth and final KC-46A test aircraft for the US Air Force's (USAF) next-generation aerial refuelling tanker programme.
The move keeps the company on track to deliver the initial 18 combat-ready aircraft to the air force by 2017.
Boeing vice-president and KC-46 Tanker programme manager Maureen Dougherty said all four test aircraft are moving through production to support the transition to ground and flight testing later this year.
The initial test flight of an KC-46 engineering and manufacturing development (EMD) tanker aircraft, without its aerial refuelling systems, is slated to take place at mid-year, followed by the first flight of a fully-equipped KC-46A tanker in early 2015.
Delivery of the first production aircraft to the air force is anticipated in early 2016.
A total of 179 tankers are expected to be delivered by Boeing by 2027 if all options under the contract are exercised.
Developed from Boeing's 767-200ER airliner, the KC-46A is a military aerial refuelling and strategic transport aircraft designed to replace USAF's ageing KC-135 Stratotankers fleet, which has served as its primary refuelling aircraft for more than 50 years.
Equipped with the Cobham centreline drogue system, integrated display system and four body fuel tanks, the wide body multimission aircraft will be capable of transporting fuel, cargo, passengers and patients, at a maximum speed of 915km/h.