Runback Ice formation
Runback Ice Formation generally occurs when thermal de-icing systems are used. The ice on the de-iced section of the airfoil melts and if it is not shed in sheets it tends to run back from the de-iced area and refreeze. As distinct from pneumatic de-icer boots, which crack the ice rather than melt it, thermal de-icers are best used as anti-icers, i.e., apply the heat as soon as icing conditions are encountered to minimise ice accretion.