Mayday and Pan calls should strictly speaking only be made on the international distress frequency 121.5 and are intended as an open transmission requesting assistance from all and any stations receiving the broadcast.
Negative...but then you go on to make the correct point.
The guidance is to do it on whatever frequency you are on - not to make the switch. If you're not in contact with anyone, then do it on 121.5.
Half your spacecraft explodes, and the call is, "Houston, uhh, we've had a problem."
It would be interesting to find out if NASA had thought to create proper R/T for an emergency in space where no other traffic existed at the time. Otherwise, I have a feeling those same astronauts would have done "the right thing" and used proper vocabulary. Having met a number of astronauts, it's amazing to see that they're all "by the book." So if we idolize their coolness, should we not also strive to their level of perfection?
Why would they care ?
Not only because of radio silence, but take a listen to the ATC Tapes following the Asiana crash at KSFO. There is Tower trying to communicate with emergency services while every damned aircraft out to 12 final is stating they are going around and what they are going to do and who they are going to talk to...not even a grain of common sense amongst them. You hear Mayday or PAN-PAN on the radio and realize that your request for direct the FAF is suddenly not the most important thing in the world...or that maybe Tower doesn't care that you're going around because that's what they expect you are going to do as a professional aviator.
A very quick trawl of accident reports will show multiple occasions where the ATC or radar facility did not realize the aircraft concerned was declaring an emergency because they failed to use the standardized phraseology
Exactly. Why take all the time of the guess work that leads to "are you declaring an emergency?" "yes, we are declaring an emergency!" "check, [callsign] declaring an emergency, state POB, fuel on board, dangerous goods and intentions" when a proper "Mayday" call will cover all of that in a quarter of the time (and distance, and fuel, and, and, and)