Originally Posted by Luckystar77
When would you use SLOW and when would you use FAST mode? According to Q400 FCOM we need to select some kind of DEICING MODE whenever SAT is below 5 C deg.
When would I need to switch from SLOW to FAST?
A. Do what the company/aircraft manuals says.
B. If the manual is silent on the specifics, select SLOW on initial ice detection and go to FAST if the ice continues to build or is not being shed quickly enough.
C. If having selected FAST you are still building more ice and/or performance is deteriorating, leave the icing conditions.
From memory the Dash 8 FCOM advised to turn the prop heats ON when encountering icing conditions but to only select the de-ice boots ON once ice was detected (by the pilot's eyes in the 100/200/300 series.)