Honeywell ALF502

The ALF502 is a geared high-bypass turbofan developed by Lycoming and subsequently supported by Honeywell. Certified in 1980, the family powered the BAe 146 regional airliner and the original Challenger 600 business jet. It later became an important test engine for research into ice-crystal ingestion.^{[1]Validation Ice Crystal Icing Engine Test in the Propulsion Systems Laboratory at NASA Glenn Research CenterNASA · ntrs.nasa.gov · Accessed 2026-09-13Open source details}

Development background

The design was associated with Lycoming's YF102 military turbofan programme. The US Air Force museum preserves a blade from the first YF102/ALF502 engine and records the YF102's use on the Northrop A-9. That aircraft lost the close-air-support competition to the Fairchild Republic A-10, while the related civilian engine continued into commercial applications.^{[2]YF-102 Turbofan Engine BladeNational Museum of the United States Air Force · nationalmuseum.af.mil · Accessed 2026-09-13Open source details}

Engine arrangement

NASA describes the ALF502-R5 as a high-bypass geared turbofan with a bypass ratio of 5.3:1 and a forty-inch fan. Its low-pressure turbine drives the geared fan and low-pressure compressor. The high-pressure compressor combines axial and centrifugal stages, with an annular combustor and a separate high-pressure turbine. The test engine represented the approximately 7,000-pound thrust class.^{[1]Validation Ice Crystal Icing Engine Test in the Propulsion Systems Laboratory at NASA Glenn Research CenterNASA · ntrs.nasa.gov · Accessed 2026-09-13Open source details}

Ice-crystal investigation

Some unmodified ALF502-R5 engines experienced uncommanded thrust reductions in high-altitude cloud near thunderstorms. Investigation led to a field modification, and the operational restriction was lifted for engines incorporating it. One instrumented engine from the 1997 flight-test investigation was retained in its original configuration, providing unusually detailed information for later research.^{[1]Validation Ice Crystal Icing Engine Test in the Propulsion Systems Laboratory at NASA Glenn Research CenterNASA · ntrs.nasa.gov · Accessed 2026-09-13Open source details}

NASA testing

In February 2013, NASA and Honeywell used that engine to demonstrate full-scale ice-crystal testing in the Propulsion Systems Laboratory. Researchers reproduced engine anomalies under atmospheric conditions corresponding to flight experience. The programme sought to improve understanding of the physical mechanism, establish effective test methods and generate data for computational tools assessing icing susceptibility in other commercial engines.^{[3]Aeronautics Research OverviewNASA · ntrs.nasa.gov · Accessed 2026-09-13Open source details}