Pratt & Whitney Canada began development of small gas turbines in the mid-1950s. Experience was first gained with the JT12 turbojet, produced by P&WA in the United States for aircraft such as the North American Sabreliner. In the late-1950s, following a survey of small aircraft manufacturers, P&WC decided to produce the PT6 free turbine engine, for both turboshaft and turboprop applications.

Initial commercial success was in the turboprop powered, fixed-wing Beech King Air, which first flew in February 1964. In 1967, foreseeing that multiple-turboshaft helicopter installations promised increased power and flight safety, P&WC began design of an engine consisting of two PT6 power sections coupled to a single gearbox. The PT6T-3 TwinPac became operational in 1970, first flying in the Bell 212 and UH-1N Twin Huey helicopter family.

This uprated TwinPac is installed in the nose cowling of a re-engined Sikorsky S-58T helicopter, and provided an extended operational envelope and improved payload capability over the original piston-powered version.