Robert, Mayday may be the official emergency call and works well throughout the world. In the US however it is a formality to be correct. Declaring an emergency does the same thing and I have heard it many times in my long career. Never mayday except at the Reno Air Races when they blow an engine. I only had two emergencies and never once have said mayday. 23,000 hrs and no maydays calls is pretty average in the US. ICAO is not so laid back.