Designed in Czechoslovakia by the Aero Group, the HC-4 helicopter is derived from the smaller HC-4 flown some years ago. Prototypes are under construction at the Chocen factory in East Bohemia but production is likely to be based in Poland. Accomodating two pilots and up to six passengers, the HC-4 is powered by a 740 shp Walter M601H. Diameter of the three-bladed semi-rigid rotor is 34 ft 8 in (10,57 m), overall length is 31 ft 10 in (9,70 m) and height is 10 ft 1 in (3,07 m).