The companion
signal to
mayday in the
communications world is
pan-pan.
Pan-pan indicates that the caller needs
assistance but that the
situation is not (yet)
life-threatening. Examples might include being totally
lost, or
adrift (in the case of a ship) but not near any known
hazards. I think pan-pan is used mostly due to its
distinctive sound, making it more likely to be heard and gain
attention, but I could be wrong.
The aviation world has another means of declaring Mayday or pan-pan; transponder settings. A setting (or squawk} of 7700 on a standard FAA Mode C transponder indicates distress to any air traffic controller who sees the aircraft's position on civil aviation radar. Finally, if you are not presently communicating with any station when the problem occurs and don't have an appropriate local frequency, you should use 121.5 Mhz which is reserved for emergency traffic and is continuously monitored.