The US Army Aviation Engineering Flight Activity operates a modified CH-47C helicopter as an airborne spray tanker for helicopter qualification tests in artificial icing conditions. The operational performance and spray cloud characteristics of the Helicopter Icing Spray System were evaluated in the course of several test programs during the 1984 and 1985 icing seasons in Duluth, Minnesota. Configuration changes made during the first two phases of this program reduced previous spray system problems of water leakage, freezing, and non-uniform flow patterns from the boom assembly. In-flight spray cloud data taken with a JU-21A aircraft using particle measuring spectrometers found peak mass concentrations in the desired 15 to 25 micron drop diameter range as well as the presence of larger drops (>50 microns) not normally found in natural stratiform clouds. Many aspects of ice formation produced on various test aircraft compared favorably to natural accretions. Ability of the artificial cloud to produce non-streamlined 'double-horn' ice shapes on main rotor blades at -5 C was substantiated for the first time.