Aircraft Icing
If frost, ice or an accumulation of snow is seen during the preflight inspection the airplane will be deiced, if accumulation is likely to develop prior to takeoff, the airplane will also be anti-iced.
Removing existing contamination is considered deicing, and adding fluid to prevent accumulation is anti-icing.
Deicing Fluid
Typically the airlines use three different types of deicing / anti-icing fluid:
Type 1
Type II
Type IV
Since the fluid is applied when the pilots are inside the airplane, the de-icers are qualified to report that all contamination is removed from the airplane, and that it is 'clean' (of frost, ice or snow), without need for a further inspection by the pilots.
Holdover Times
Once fluid has been applied, useful times have been established after which the airplane must have the fluid reapplied, this time period is the 'holdover time'.
The time can be read from a chart provided to the pilots, and differs depending on the concentration of the fluid used.
