Mad(flt)Scientist, "Question: does the entire ADR section of an ADIRU "fail" as one unit? That is, having detected that it is producing "unreliable" airspeed data (through the ADR DISAGREE method) is the entire ADR output regarded as suspect by other systems?"
The communication from the Air Data (Module, Computer) to the transponder, for example, is on an Arinc 429 serial digital data bus. There are several words transmitted in sequence, each with its own identifier and validity state. CAS, IAS, TAS, SAT, Pressure Altitude, Baro Altitude, Vertical Speed, etc. will be on the bus.
The transponder will pick off Pressure Altitude, and ignore the rest. The ADC transmits all words repeatedly. If the airspeed goes invalid, for example, Fail Warn will be indicated in the Sign Status Matrix of that word.
Therefore, an iced pitot will have no effect on the transponder or any other device that uses Altitude, nor on the TCAS, which is even farther removed.
GB