Seeking to expand its family of civil helicopters by adding a six-seat aircraft to its two-/three-seat Model 269/300 series and four-/five seat Model 500 series without having to make a major investment of capital, in mid-1981 Hughes proposed a 'wide-body' version of the Model 500. The new model was to have a 38cm longitudinal plug inserted in the fuselage but was to retain the powerplant installation, rotor system, tail boom and T-tail surfaces, and most of the fuselage of the Model 500D virtually unchanged.

Market conditions were not favourable in late 1981 and early 1982 for the launch of a new helicopter. Moreover, the corporate re-organization and the decision of the parent organization, The Hughes Corporation, to divest itself of Hughes Helicopters, Inc, also made the development of a new product ill advisable. Consequently, all work on the Model 600X was terminated before Hughes Helicopters was acquired by McDonnell Douglas Corporation.

Rene J. Francillon "McDonnell Douglas Aircraft since 1920: Volume II", 1997

Technical data for Hughes 600X

Rotor diameter: 8.08m, length: 9.30m, height: 2.59m, take-off weight: 1361kg, empty weight: 651kg, cruising speed: 253km/h, hover ceiling, OGE: 2255m, max range: 790km