a./ IF you are in such "DS", then the last thing you want to do is frab about with your transponder UNLESS a/ told to do so, or b/ in the FIR and are in [really] desperate need of assistance. . .b./ Same again. Pan alerts ATC, then you inform. Mayday, is [ultra] DS and the fan is about to get covered.. .The "trite" answer is to talk to the ATSU that is [hopefully] providing a service.. .Hope this helps. .we aim to please, it keeps the cleaners happy