TYPE: Medium transport/multirole.

PROGRAMME: Design study revealed by McDonnell Douglas (now Boeing) in September 1996 for a potential replacement for the Lockheed Martin C-130 Hercules. Original study envisaged aircraft with four 8,850 kW (12,000 shp) turboprops fixed to wing, which tilted 15° for take-off and 45° for landing; potential in-service date of 2020. Those studies provided basis for No-Tail Advanced Theater Transport (NOTAIL ATT) Tilt-wing Super Short Takeoff and Landing (SSTOL) or 'Super Frog' as project was originally known. Advanced Medium Transport (AMT) name adopted by mid-2002, although had evolved further, into Advanced Tactical Transport (ATT), by early 2003.
Concept revealed in September 1998, with 39 m (128 ft) span aircraft designed to carry up to four times the payload of the C-130J Hercules and use runways as short as 183 m (600 ft). Baseline requirement is delivery of 27,215 kg (60,000 lb) load on to 229 m (750 ft) of rough airstrip, 1,220 m (4,000 ft) AMSL in 35°C (95°F) ambient temperature. Signature of co-operative research and development agreement (CRADA) between Boeing's Phantom Works and USAF Research Laboratory at Wright-Patterson AFB, Ohio, in December 1998 paved way for development and demonstration of 'enabling technologies' that could lead to production-configured aircraft; subsequently, in late 2000, Boeing also concluded development agreement with DARPA.
Fuselage interior width is 6.4 m (21 ft) and proposed ATT will be able to accommodate various loads up to a maximum of about 36,285 kg (80,000 lb), including one AH-64 Apache or two RAH-66 Comanche helicopters; or up to 10 cargo pallets; or 40 fully equipped soldiers. Wing features four widely separated podded turboprop engines in the 8,950 kW (12,000 shp) class, each driving eight-blade propeller. Wing originally pivoted about lateral axis near rear spar, with tilt used to increase lift during take-off and landing. Directional control of tail-less design uses similar system to B-2 bomber, which has split flaps. By early 2000, however, design had progressed to forward-swept (7 to 9°) wing, pivoted at leading-edge and tilting downwards at trailing-edge, with further refinements by second quarter of 2001 adding small horizontal tail surfaces and adopting C-17-style fuselage.
Initial wind tunnel testing of subscale model completed by end of 1998, followed by further trials with a 7 per cent subscale model during 1999; latter included tethered and untethered tests which began at Gray Butte, California, on 5 June. Further wind tunnel testing of latest configuration completed in January 2001, with Boeing planning to conduct manned simulations and powered wind tunnel tests with larger models in 2001-03. In first quarter of 2003, Boeing revealed that it was considering resurrecting a McDonnell Douglas YC-15 prototype and modifying it to serve as a tilt-wing technology demonstrator. The most significant alterations would involve installation of a forward-cranked wing that could rotate the trailing-edge downwards by up to 20° and the switch from turbofan to turboprop engines. If it goes ahead, the demonstrator could be flying in early 2005, with the primary objectives of proving the viability of the tilt-wing super STOL transport aircraft concept and of validating use of cyclic controls on a fixed-wing aircraft.
If project is proceeded with, Boeing optimistic that production aircraft could be operational in 2015, with ATT a potential candidate for USAF MC-X special operations aircraft requirement.