Originally Posted by
Deeday
Has Emergency replaced Mayday in the US standard phraseology?
Yes....
Not really, the official terminology is similar to the UK. However, it seems to be omitted from almost all emergency transmissions in the US (Even commercial).
The common (though not correct) phraseology is
'I have/am declaring an [low, medical, engine out, low power, ...] emergency'
or
'Ah, this, uh, Cactus 1539. Hit birds, we lost thrust in both engines. We're turning back'