An interim twin-engine conversion of a Model 214 flew on 15 February 1977 in Texas,[4][5] Testing was successful, and Bell decided to press forward with a definitive twin-engine Bell 214ST, with a fuselage stretched by 30 in (76 cm) and a revised main rotor of greater diameter.

By this time the new helicopter had attracted sufficient interest from other potential customers for Bell to continue with the project and build the 214ST at their Dallas-Fort Worth facility instead.

Type certification from the FAA and CAA for visual and instrument flight rules was awarded in 1982.

The Bell 214ST has a larger, stretched fuselage with seating for 16-18 passengers,[10][11] and two 1,625 shp (1,212 kW) GE CT7-2A engines.

[12] The helicopter introduced some ground-breaking innovations for Bell, including a one-hour run-dry transmission, fiberglass rotor blades, elastomeric rotorhead bearings, and the option of either skid or wheeled landing gear.