This glossary is written for virtual airline and flight simulation use within Virtual Air Canada Airline. It is not intended as a real-world aviation reference.
HOT
Hold-Over Time
Hold-Over Time is the estimated time that a de-icing or anti-icing fluid applied to an aircraft will remain effective in preventing the accumulation of frost, ice, or snow on critical surfaces. HOT is not a guaranteed period of protection - it is an estimate based on the type of fluid used, the outside air temperature, and the precipitation type and rate at the time of application. Transport Canada and the FAA publish HOT guidelines in table form, and ground crews and flight crews consult these tables before departure to establish whether a second application is needed.
Type I fluids (orange, unthickened) have short hold-over times, often only a few minutes in active precipitation, and are primarily used for de-icing rather than anti-icing. Type II, III, and IV fluids contain thickening agents that extend the HOT significantly and are used as anti-icing treatments. The crew must monitor elapsed time from fluid application and confirm the aircraft’s critical surfaces are still clean before taking the runway - this check is called the pre-takeoff contamination check or “clean aircraft concept.” If the HOT has been exceeded, a new de-icing treatment is required before departure.