PT6T Twin-Pac, a unique coupled redundancy system
The Pratt & Whitney Canada PT6T-3 Twin-Pac engine is a unique arrangement: 2 independent PT6A engines coupled to a single combining gearbox. If one engine fails, the second keeps delivering power through the same gearbox, redundancy without the need for separate gearboxes as in a conventional twin. Combined power of 1,800 shp limited by the gearbox to 1,290 shp to preserve service life. The system is also used on the Bell 412, a Bell/PWC patent.