The Lycoming T55 (Company designation Lycoming LTC-4) is a turboshaft engine used on American helicopters and fixed-wing aircraft (in turboprop form), since the 1950s. It was designed at the Lycoming Turbine Engine Division in Stratford, Connecticut as a scaled-up version of the smaller Lycoming T53. Both engines are now produced by Honeywell Aerospace. The T55 also serves as the core of the Lycoming ALF 502 turbofan. Since the T55 was first developed, progressive increases in airflow, overall pressure ratio and turbine inlet temperature have more than tripled the power output of the engine.