Chapter 3 - Deicing/Anti-icing Fluids

1.  The most common techniques for removing frozen precipitation from aircraft critical surfaces and protecting the aircraft against re-contamination are accomplished with aircraft deicing and anti-icing fluids called Freezing Point Depressant (FPD) fluids. There are a number of FPD fluids available for use on commercial aircraft and, to a lesser extent, on general aviation aircraft. Deicing and anti-icing fluids should not be used unless approved by the aircraft manufacturer.

2.  Although FPD fluids are highly soluble in water, they absorb or melt slowly. If frost, ice or snow is adhering to an aircraft surface, the accumulation can be melted by repeated application of proper quantities of heated FPD fluid. As the ice melts, the FPD mixes with the water, thereby diluting the FPD. As dilution occurs, the resulting mixture may begin to run off the aircraft. If all the ice is not melted, additional application of FPD becomes necessary until the fluid penetrates to the aircraft surface. When all the ice has melted, the remaining liquid residue is a mixture of FPD and water at an unknown concentration. The resulting film could freeze (begin to crystallize) rapidly with only a slight temperature decrease. If the freezing point of the film is found to be insufficient, the deicing procedure must be repeated until the freezing point of the remaining film is sufficient to ensure safe operation.

3.  The deicing process can be sped up considerably by using the physical energy of high-pressure spray equipment and heat, as is the common practice.

Note:  It is the heat contained by the Type l (de-ice) fluid and the hydraulic force that removes the frozen contaminants. The glycol provides some protection during precipitation conditions until Type ll, III or IV fluid is applied.