in mid-1970, the usaf began a paper study, the tactical aircraft investigation (tai), with boeing, mcdonnell douglas, and other companies to look at possible tactical transport aircraft designs. this study was a precursor to what became the advanced medium stol transport program. as a part of this program, boeing began to look at various high-lift aircraft configurations. boeing had earlier proposed an underwing externally blown flap solution for their competitor for the lockheed c-5 galaxy, and had put this to good use when they modified their losing entry into the boeing 747. they had also done studies with the original boeing 707 prototype, the boeing 367-80, adding extensive leading and trailing edge devices using blown flaps. for the tai studies, boeing again looked at those mechanisms, as well as new mechanisms like boundary layer control. however, none of these studied designs were particularly appealing to boeing.