The Williams FJ33 is an American family of turbofan jet engines intended for use in very light jet aircraft.

[2] Engine configuration is a single stage fan, with booster stage, driven by a two-stage LP turbine, supercharging a centrifugal HP compressor, driven by a single stage HP turbine.

The FJ33 has a dry weight of less than 300 lb (140 kg), overall diameter of 18.36 in (466 mm), 38.43 in (976 mm) overall length, and produces between 1,000 lbf (4,400 N) and 1,800 lbf (8,000 N) static thrust.

Specific fuel consumption at 1,200 lbf (5,300 N) thrust (SLS, ISA) is understood to be 0.486 lb/(lbf⋅h) (13.8 g/(kN⋅s)).

Iran apparently reverse engineered a variant, and is using it as high endurance UAV powerplant.