Frozen contaminants are most often removed in commercial operations by using Freezing Point Depressant (FPD) fluids.
It is the heat contained by the Type l (deice) fluid and hydraulic forces (high pressure spray equipment) that removes the frozen contaminants.
It is imperative that take-off not be attempted on any aircraft unless the PIC has determined that all critical surfaces of the aircraft are free of frost, ice or snow contamination.
Aircraft deicing/anti-icing fluids consist of four types. They are Type I, II, III, and IV.
Deicing fluids are typically ethylene glycol, diethylene glycol or propylene glycol based fluids containing water, corrosion inhibitors, wetting agents and dye.
Anti-icing fluids are similar in composition except that they also contain polymeric thickeners. They are formulated to prevent formation of unabsorbed frozen contamination for a longer period of time than deicing fluids; however, the protection is still for a limited period of time.
The operator is ultimately responsible for ensuring that only qualified fluids are used.
If the colour of the fluid being applied to the aircraft is NOT the colour anticipated, the procedure should be stopped and the situation investigated.
Type I fluids are used for deicing or anti-icing, but provide very limited anti-icing protection.
Type II fluids are designed to remain on the wings of an aircraft during ground operations, thereby providing anti-icing protection. This fluid should be used on aircraft with rotation speeds (Vr) above 100 knots, unless otherwise specified by the aircraft manufacturer.
Type III fluids are designed for aircraft that have a shorter time to rotation and this should make it acceptable for some aircraft that have a Vr of less than 100 knots unless otherwise specified by the aircraft manufacturer.
Type IV anti-icing fluids meet the same fluid specifications as the Type II fluids and have a significantly longer HOT.
The LOUT for a given fluid is the higher of:
The lowest temperature at which the fluid meets the aerodynamic acceptance test for a given aircraft type, or
The actual freezing point of the fluid plus its freezing point buffer of 10°C, for a Type I fluid, and 7°C for a Type II or IV fluid.
Some Type II or IV fluid residue may remain throughout the flight and this residue should be cleaned periodically. It is suggested that the use of heated Type I fluid/water high pressure washing may alleviate the occurrence of fluid dryout.