Thanks Schro. I'm used to know the international limits of my planes, but not the national ones. In the EU, it usually does not matter(though, for the SW3.....), countries are too small anyways. If, for my next game, I go to a bigger nation, I might pay attention.
Anyways, my current rule for a thumb is :
_For a SW3, be cautious above 280NM
_For a ERJ, be cautious above 600NM
_For a Ejet, be cautious above 12000M
_For a 737, be cautious above 2000NM
"be cautious" means "don't go there if demand exceeds capacity, or if there is any kind of opposition". I closed recently a EGPF-KMSP who earned a lot of money for 2 decades, and then went obsolete. I don't have anything bigger than a 737 in that game. Always sad, but you have to choose between buying a few overpriced 777/350 for a few prestige routes, and flooding the european market with SW3(lots of fun, even if overall profit is really low). My previous game, I had 777. Some of them were making good money, many were not, and half a billion a piece is a big deal, for an average-sized company.
Previous game, also, I had zounds of A148E, flying routes up to 2200NM. Then around, 2023, I noticed they suddenly stopped making any money on routes above 1800NM. Too small penalty + increasing petrol prices. Those medium planes are really getting drunk around 2000NM, where they drink suddenly far too much petrol. Replaced them with over-sized MAX7. Profitability did jump up. Yeah, above 1800NM, on a route with 80 demand, after 2020, a MAX 7 is much more profitable than a A148E. Even if you can buy only one for the price of 6 A148E.....(But the B variant, limited to 1790NM, prevents you from doing (too) stupid things. If costs go below 20M$, you can go there, it's actually good stuff. The A variant is good even for newbies)
Of course, being a dumbass, I began again this game, with overpriced Ejets instead of underpriced A148(London City is a big trap. You can easily build a fortress with 75% market share there, but it forbids you going with better fleet types. Of course, if there is a trap, I HAVE to jump in to be sure it's really a trap. I even tried IL62M, one day. That one was painful. 92 VLA pilots for 2 planes at maximum wage. Don't. It nearly killed me).
TL;DR : find the limits of your planes, and only go beyond if you know what you do. And even if you know what you do, you might have nasty surprises.