Three calls of "pan-pan" in radiotelephone communications, is used to signify that there is an urgency on board but that, for the time being at least, there is no immediate danger to anyone's life or to the vessel itself. This is referred to as a state of urgency.
Three calls of "Mayday" means that there is imminent danger to life or to the continued viability of the vessel itself.
Thus "pan-pan" informs potential rescuers (including emergency services and other craft in the area) that a safety problem exists whereas "Mayday" will call upon them to drop all other activities and immediately initiate a rescue attempt.
Any failure of multiple systems rendering the aircraft in a single system state should thus be considered a potential Mayday