Typically, deicing fluid comes in two "flavors", Type I and Type IV
Type I is usually orange in color, and is mixed 1 part water to 1 part glycol ( i.e. 50/50 mix). Depending on the airline and the circumstance, this fluid either comes pre-mixed or is mixed in the deicing truck itself. This fluid is heated in the deicer to at least 140 degrees at the nozzle, and is sprayed on the aircraft to remove contaminants ( i.e. frost, snow, slush).
is green in color, is 100% glycol, and has the consistency of the Nickolodeon slime. Its not necessary to heat Type IV
, but it always can only be applied to a "clean" aircraft ( one that has already been sprayed with Type I). Due to the thick consistency of the fluid, it is not sprayed, but instead squirted out of the nozzle. Typically, it is only applied to critical surfaces of the aircraft, such as the wings and horizontal/vertical stabilizers.
As somebody mentioned earlier, the start/stop time of the deicing event is recorded and given to the pilot-in-command to determine the holdover time of the deicing fluid. This time starts when the final application of fluid (either Type I of IV
begins) and extends until the fluid is no longer able to prevent accumulation on the ground. The aircraft must be airborne by the time that the holdover time is expired. I know that for light freezing rain, the holdover time is like 18 minutes. Therefore, if the aircraft is not airborne in 18 minutes from when the Type IV
application began, the aircraft will need to return to the deicing pad and the whole process will need to begin again.
In a deicing event, the ground controllers will talk to each flight and find out when their holdover time expires, and then try to expedite and get the aircraft airborne before the time is up.
Hope this helps you out