Suppose I'm flying VFR in class G (uncontrolled) airspace, monitoring the local CTAF frequency while doing so. Maybe I'm alone in doing circuits around the local airport, or maybe I'm practicing navigating by landmarks, or maybe I'm on a cross-country flight from A to B. Either way, there is no one else in the immediate vicinity making themselves known on the radio, and (unlike in controlled airspace) there's no obvious ground station that I can call and expect to get an answer from.
Now, I, or someone else onboard, spots a fire on the ground some distance away.
A good first step then seems obvious, to go closer to get a better look. Now suppose that, on closer inspection, this does indeed appear to be an out-of-control fire with no firefighters on site. This could mean either that nobody yet knows about it, or that rescue services have been alerted but are still on their way.
It could be a structural fire, or a forest/field/grassland/etc. fire. To the extent that this makes a relevant distinction, it'd be great if answers addressed both types. (Both of these have happened recently in my immediate area, though I don't think they were initially reported by aviators.)
For me, a thousand feet or more above ground, what's the next step?
The aircraft isn't in any immediate danger, so from the perspective of the aircraft and its occupants, it's not an emergency or even urgency situation. However, there's certainly risk to property, and possibly people, on the ground.
Should I dial in 121.5 on the radio and call mayday? Or pan-pan on 121.5? Or should I use some other frequency, such as that of the local area control if I were to climb straight up into controlled airspace? (They would also be monitoring 121.5, so I would effectively be reaching the same people.) Mayday, pan-pan, or not? Or something else entirely?
Not doing anything in particular and just going on with my day doesn't seem like the right thing to do in such a situation.
Looking at my radiotelephony textbook, urgency traffic (pan-pan) includes situations relating to the safety of a "vehicle" (not just the aircraft, but specifically including any aircraft) or for a person onboard or within sight, but that do not require immediate assistance. Emergency traffic (mayday) includes situations involving "serious and/or immediate danger" (unspecified as to what) where immediate assistance is required.
I'm interested primarily in answers pertaining to the EU.