Originally Posted by
ballyboley
Sorry, didnt RTFQ! I was referring to 737 where I had an engine cowl ice stuck open, but they downgraded us to CAT1 for some reason. I'm not sure the loss of GA thrust would be the reason as surely you would have anti-ice on during most CAT3 and therefore subsequent go around's anyway?
Well, the FAA MMEL on the TCCA website doesn't appear to have that CAT1 downgrade as a specific item (see
pages 142 to 146 depending on the specific model).
There are significant thrust penalties though, and a limitation on operation in icing. Therefore, I might suggest:
If you are operating a CATIII approach IN ICING, you already can't do it per the icing limitations.
If you are operating and NOT IN ICING, the thrust deficit may mean that any weight restrictions applicable to CATIII have to be recalculated.
If, as you suggest, the vast majority of CATIII is in icing anyway, the operator may have elected to impose the CATI degrade as a more conservative version of the MMEL (The MEL can always be more conservative, but never less, than the MMEL)