Can the controller declare an emergency too? I overheard an exchange where a water cooled light piston had dumped it's coolant over the side over mountainous terrain. The VFR pilot was not keen to say MAYDAY or even PAN (which is not even taught in the USA). The pilot was obviously not a "professional", whatever that means
, and maybe that was very relevant to what happened.
The controller eventually said something to the effect of "XXX Approach is declaring an emergency. NXXXX squawk 7700, cleared into the XXX Class B, if able maintain altitude and turn right heading 270, contact me on xxx.xx, etc etc etc"
So although he could not force the pilot to say MAYDAY, the controller was able to escalate things to "emergency" and get the ball rolling so he could make things happen. This was in the States and the plane landed safely.