Many people are using the ACARs data at ‘face value’ without considering what precisely is indicated. What does the pitot readout mean; e.g. is it an indication of pressure mismatch or a failure of the anti icing heater system, etc?
Depending on what and how a problem is detected by the fault system, the specific problem could range from an electrical failure (heater), a leak, or icing (data mismatch). Speculation might then be based on the better understanding of these aspects .
I am familiar with icing problems with TAT probes. Some probe types suffered from ice ingestion in similar met conditions to those reported. These probes did not fail, but because the airflow path was restricted by micro ice crystals the probe erroneously measured ‘0’ deg C – the temperature of the static ice, opposed to the dynamic airflow flow. Presumably, without knowledge of a comparison or memory value, this would not trigger a ACARs fault.
Thus in these rare conditions, TAT can change value significantly (-50 to 0) without change in aircraft condition; whereas ‘Classic’ pitot icing normally traps pressure and a problem is not identified until there is a change in the aircraft state – speed / altitude.
Aircraft with multiple TAT probes could encounter either single or multiple problems. Systems using TAT information (e.g. ADC) might be able to identify a difference in TAT values and thus ‘flag’ a fault, but often (with single systems) the erroneous TAT is used by the aircraft systems.
It may be of interest to understand where and how TAT is used in the A330 and, together with the pitot system, how faults are generated. e.g. does the ADC use TAT for Mach / Alt correction? Would a mismatch of erroneous TAT cause the ADC’s to ‘miscompare’ – the resulting fault leading to the reported FGC, rudder limiting, and control ‘faults’?
The conditions for TAT probe icing can be encountered at considerable distances from a Cb; they are not easily identifiable with WXR, simultaneous aircraft icing is unlikely. The very fine ice particles (occasionally mixed with water) can be found in and below the anvil of large storms, hence a deviation of 20-30nm from the Cb core might not be sufficient to minimise the icing risks.