@DozyWannabe. TCAS doesn't receive any speed input whatsoever. It calculates closure rates based on comparing time it takes to send a signal and receive it back at the antenna.
Post amended because of bad wording
TCAS does have one air data input for Mode C (barometric altitude) coming from the Static Port. It would be very unusual for a Static Port (which is flush on the fuselage) to ice over.
So as a source of failure for the TCAS I think not likely.
Last edited by Shaka Zulu; 30th May 2011 at 20:52.