The Rolls-Royce RB.183 Tay is a medium-bypass turbofan engine, developed from the RB.183 Mk 555 Spey core and using a fan scaled directly from the Rolls-Royce RB.211-535E4 to produce versions with a bypass ratio of 3.1:1 or greater.

The newest variant is the 611-8C, which has cast HP1 turbine blades, larger fan from the 650-15, structural by-pass duct and FADEC.

Thrust: 13,850 lbf (62 kN) Aircraft: Tay 611 entered service in 1987 on the Gulfstream IV/IV-SP, for which it is the exclusive powerplant.

Thrust: 13,850 lbf (62 kN) Aircraft: Fokker 70 from 1994, Fokker 100 from 1988 Thrust: 15,100 lbf (67 kN) Aircraft: Originally designed to re-engine the BAC One-Eleven (650-14, only two made; both have since been converted to 650-15 standard.

Conversion from three JT8D-7 to three Tay 651-54 was carried out by the now defunct Dee Howard Aircraft Maintenance Company in San Antonio, Texas, for the United Parcel Service, but all aircraft have since been withdrawn from service.