O60sCOTD  

For many years Soloy Conversions in the United States has been involved in the convertsion of aircraft and helicopters to turbine power, using the Allison 250 range of turbines. The Company, founded by Joseph Soloy, commenced conversions of helicopters in the 1970s, commencing with the Hiller UH-12E. Work proceeded for eight years before certification of the UH-12 with an Allison 250-C20 was received in April 1975.  Work immediately commenced on conversion of the Bell 47 series and following proof-testing of the airframe, the Bell 47 received its Supplemental Type Certification in September 1978.