TAT temp increase
Re: the serious “a sudden and significant rise in the outside air temperature” (#608 R&N) and above.
Subsequent to the Australian report, the majority, if not all of the temperature rise was shown to be an apparent rise due to a frozen TAT probe – the probe indicated the ice temperature and not that of the atmosphere.
Following several other incidents BAe/Honeywell conducted tests in and near large Cbs to investigate the engine icing problem. As a result, the affected engine variant was modified.
The initial flight tests showed that the problem did not per se occur in the tops the Cbs, instead it was the water/ice concentrations in the out flow of these large storms (in the anvil) which presented a threat over a large area. The analogy is of smoke spreading out from a chimney.
The erroneous TAT in BAe146 aircraft was not deemed a significant risk. IIRC there was only an input to the TMS takeoff mode and a temp display in some FMS variants. Thus, the problem was documented and risks agreed with certification authorities; all engines were modified by AD.
At that time the industry did note similar problems with engines and TAT/pitot probes in other aircraft types, but (at that time) the safety concerns were not significant, certainly not in the same category as the multiple engine ‘rollbacks’ with the 146.
The TAT problem persisted, but industry follow-up identified differences between probe manufacturers and probe design, i.e. aspirated / non- aspirated versions.
I suspect that TAT is used in many modern computations and hence there are multiple sensors. Assuming that individual sensors do not ice at the same time / rate then disparities in temperature or in the parameters using TAT could trigger comparator alerts or even system lockout through data disagreement.
Many of the reported ACARs messages appear to represent this type of problem.