Definition

The estimated time that deicing/anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the critical surfaces of an aircraft.

Source: ICAO Annex 14

Description

Holdover time (HOT) begins when the final application of deicing/anti-icing fluid commences and expires when the deicing/anti-icing fluid loses its protection effectiveness. It is determined by the extent to which it is expected that applied fluid will remain active on the aircraft surfaces; active fluid must be able to provide protection from the accretion of frozen or semi-frozen contaminants in the prevailing conditions. Holdover Time begins at the start of the anti icing operation. If a two-step operation is used, then it begins at the start of the final (anti-icing) step. By definition therefore, holdover time will have effectively run out when frozen deposits start to form or accumulate on treated aircraft surfaces.