In 1989, the US Congress directed the USAF and the US Navy to procure a single replacement aircraft for the USAF Cessna T-37B and the Navy Beechcraft T-34C trainers. Both services' trainers had been purchased originally in the 1950s and 1960s, and the need for more modern aircraft was apparent. Since the primary pilot training requirements in both services were similar and there was an overall push for more "jointness" to unify operations in the various services and to conserve precious defense procurement dollars, Congress mandated the joint program over initially strong military objectives.

The basic requirements for the joint USAF-Navy trainer and the associated fielding schedule were defined in the Department of Defense's 1989 Trainer Aircraft Master Plan (TAMP). The TAMP also dictated that the new aircraft must be a Non-Developmental Item (NDI)—no from-the-ground-up design and development concepts need apply. From the outset, this seemed to limit the field to foreign contenders, since it seemed that none of the US aircraft manufacturers had a suitable aircraft adaptable to the military needs.

In the early 1980s, under the Next Generation Trainer program, the USAF had attempted to replace its Cessna T-37s with the Fairchild T-46, an aircraft that closely resembled the T-37 in general configuration and performance. Both aircraft were approximately the same size, had side-by-side seating arrangements, had long straight wings, and were powered by twin jet engines. The two prototype T-46As, however, were plagued by one problem after another (including performance shortcomings) during flight testing at Edwards AFB, California. Finally, with resolution of the problems still uncertain, the USAF terminated the contract on 13 March 1987. The entire episode left a residual bad memory in the minds of many senior officials, although the need to replace those old T-37s remained unfulfilled. By 1994, the USAF T-37 fleet of 600 aircraft averaged 32 years of age and was flying an average of 500 hours per year. The original T-37 design had been for a 8,000-hour airframe, which had been extended to 18,000 hours. By 1998, the average T-37 will have loggged those 18,000 hours and will need replacing to avoid serious safety problems.

The US Navy, meanwhile, had pursued an advanced trainer replacement for its capable but worn-out Rockwell T-2 Buckeyes and McDonnell Douglas TA-4J Skyhawks. The winner of that competition was the BAe Hawk trainer, manufactured in the US by McDonnell Douglas as the T-45A Goshawk. This program, alas, was also not without its problems as the missionization of the proven Hawk produced an overweight and underperforming aircraft. Eventually, those problems were corrected, but once more the US military had failed to impress Congress with its skill in developing something as simple as a training aircraft.

The initial Joint System Operational Requirements Document (JSORD), a rather general treatise on the services' expectations for the new aircraft, was issued in October 1991. The first of two editions of the final Operational Requirements Document (ORD) for the Joint Primary Aircrew Training System (JPATS) was published in mid-1992, with the final edition issued in January 1994. The aircraft manufacturers, faced with too few potential military contracts for the number of companies in the market, wasted no time forming teams and proposing solutions to meet the ORD specifications.