The National Aeronautics and Space Administration (NASA) DC-8 airborne sciences research airplane inadvertently flew through a diffuse volcanic ash cloud of the Mt. Hekla volcano in February 2000 during a flight from Edwards Air Force Base (Edwards, California) to Kiruna, Sweden. Although the ash plume was not visible to the flight crew, sensitive research experiments and instruments detected it. In-flight performance checks and postflight visual inspections revealed no damage to the airplane or engine first-stage fan blades; subsequent detailed examination of the engines revealed clogged turbine cooling air passages. The engines were removed and overhauled. This paper presents volcanic ash plume analysis, trajectory from satellites, analysis of ash particles collected in cabin air heat exchanger filters and removed from the engines, and data from onboard instruments and engine conditions.Grindle, Thomas J. and Burcham, Frank W., Jr.Armstrong Flight Research CenterASHES; HIGH ALTITUDE; PLUMES; TURBINE ENGINES; VOLCANOES; DC 8 AIRCRAFT; DAMAGE; FAN BLADES; FLIGHT CREWS; HEAT EXCHANGERS; RESEARCH AIRCRAFT; SULFUR DIOXIDES; FLIGHT PLANS; ENGINE TESTS...