Chapter 5 - Ground Crew Supplement

FPD Temperature Buffer

31.  Temperature buffer is the temperature difference between the freezing point of the fluid as applied, and the ambient temperature. Remember from Part One that this buffer allows for absorption of precipitation.

32.  Generally, the holdover time is increased with an expansion of the temperature buffer. Therefore, if the choice is available, use the maximum buffer. However, greater buffers require the use of more glycol, which is more costly and which increases the burden for collection and processing of FPD spillage and runoff. FPD fluid mixtures and their attendant buffers should be determined after consideration of the following factors in the listed order of priority:

  • Safety;
  • Environmental impact;
  • Cost.

33.  For SAE Type I fluids, the freeze point buffer of the anti-icing should be as great as possible but not less than 10°C (18°F).

34.  For SAE Type II, III and IV, the freeze point buffer should not be less than 7°C (13°F).