Originally Posted by
Lord Farringdon
I just read also that pitot tubes can also be affected by this which tends to lead to transient and spurious air data readings.
Total pressure pitot icing is less of a concern, although it does happen (AF447). With pitot tubes, it's pretty easy to address with proper design - more heat and/or moving the heat around (and pitot tubes use a lot of heat - typically 500-1000 watts each). TAT is a lot harder since you don't want the probe heat to interfere with the temp measurement. As VinRouge notes, TAT reading around zero C is a common symptom of ICI - ice forms around the TAT probe, with liquid near freezing water at the temp sensor. When investigation suspected ICI related engine events, TAT was pretty much the first thing we looked at.
Combination PT/TAT probes (commonly used in the inlet of EPR engines) are also problematic - again due to the requirement to keep the probe heat from affecting the temp measurement. Unheated TAT probes (normally used in the inlet of N1 engines) don't have issues with ICI, although conventional icing can cause issues.