Airplane-laboratory, providing opportunities, unprecedented, from the very beginning of the development of engine building. Although only the second 747SP is first used for testing in the business aviation segment, it is the first multi-deck wide-body aircraft with an additional half-plane for testing engines installed on it. Compared to the first 747SP, where the tested engine was installed at the nominal place of attachment of power plants, to the position No. 2 on the inside of the wing, an additional half-plane makes it possible to test the engines with attachment to the fuselage (both turbofan and turboprop), and also allows testing power plants with fastening to the wing.
Overview from Pratt & Whitney