A coal-powered CitationJet? It just might happen. Williams International, the turbofan engine manufacturer, has completed an extended engine run of one of its FJ44-3 turbofans running fuel made from coal. The tests, which included 21 hours of operation and 118 operating cycles, were extremely promising and confirmed, Williams said, the promise of the FJ44, a popular small turbofan engine, to take advantage of alternative fuels in the future. The tests required no modifications to the engine or the test stand.