Aeronautical Engineers, Inc. (AEI) is a global leader in the aircraft passenger-to-freighter conversion business and is the o ... ldest conversion company in existence today. Since the company’s founding in 1958, AEI has developed over 128 Supplemental Type Certificates (STCs) and has modified nearly 500 aircraft with the STCs. AEI helps its customers extend aircraft life and increase the overall value of aircraft assets by continuously focusing on dependable and flexible product offerings. AEI currently offers passenger-to-freighter conversions for the Boeing 737-800, 737-400, 737-300, 737-200, CRJ200 and MD-80 aircraft. read more