Yes that is quite true, I didn't like to stick my neck out about the USA ones in case I was wrong about them. The other thing to note about UK mercy flights is that they fly the direct route and ATC give them the green light and priority if their route takes them through any controlled airspace. I use airband scanner when I'm out photographing aircraft at my local airfield, or major airports and airshows and they can be frequently heard on the radio informing the ATC of their intention minutes before appearing on scene. The ATC then instantly tell all aircraft to give way and even planes doing air displays are told to halt their display with immediate effect to stand down and vacate the area until further notice. Whats is even more amazing is that these air ambulances are all run by charities, UK Government will not fund them
[/quote]Interesting. US ATC has instructions/job orders to prioritize air ambulance flights above all flights other than aircraft in distress. Flights using call sign "Medevac" (civilian) or "Lifeguard" (now deprecated in favor of Medevac, but old habits die hard with some) are prioritized above all non-emergency (think "non-Mayday") traffic, including over Presidential traffic. Flights using "AirEvac" or "Hosp" which request priority are prioritized the same as "Medevac" above. It's intended to be used when responding to medical emergencies (first call to an accident scene,
carrying patients, organ donors, organs, or other urgently needed lifesaving medical material). We've got an air ambulance station on the field I'm based at and those crews, without being jerks, get whatever what they need. They will sometimes specifically indicate to ATC that they're on a positioning or training flight (to clarify when they don't need any priority).
The other type of medically-related transport are our networks of charitable transport (Angel Flight, Air Care Alliance, and similar organizations). Those flights use a Compassion call sign on mission and will generally receive no special priority over other civilian flights. (However, special priority for airspace access seems to be much less frequently needed in the US as I am rarely denied airspace access even as a normal civilian flight.)
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In the UK they use a different callsign only when on an emergency, this gives them priority when needed but not when they just want to get home for tea. We had Prince William flying one for a while here.