Sikorsky S-76 helicopter model PHI. Growing demands for transport helicopters in support of offshore energy operations led Sikorsky to initiate worldwide market research to establish the requirements of such operators. In 1975 Sikorsky began the development of a 14-seat commercial helicopter designated Sikorsky S-76, and later named Spirit. The first of four prototypes were flown on March 13, 1977. The improved S-76B was powered by Pratt &, Whitney PT6B-36 turboshafts. The alternative to the S-76B is the S-76C powered by Turbomeca Arriel 1S1 turboshafts.