1) Does it impact you when your flight is the only flight available? I could understand that if there is a choice of 2am and 10am flight, passenger would choose 10am, but what if he has no choice? Why would passenger load go down? - you need to fly and there is only one flight available...
It doesn't really matter if your red-eye is the only flight available. The demand model isn't quite that smart. Besides, if the demand is 200, that's "200" if
if you're flying at the price and time that they want to fly at -- it's not literally 200 people lined up at the airport waiting to go no matter the time or price. It's assumed if your timing or pricing isn't good enough, they simply choose not to go or make alternate arrangements.
It can still be quite profitable though with a high CI (70+) and once your RI gets up there, so there's no reason to avoid it if there's no other options.
2) Does it equally impact domestic, international and intercontinental flights? The logic would be that the longer you fly, the less you care... if you get to fly 15 hours, you less picky that your flight arrives at 4am...
The longer the flight, the less they care. Domestic or International isn't of concern, it comes down to flight length that determines their tolerance to the flight times. But they seem much more tolerant of poor arrival
times than poor departure times. They're okay with arriving someplace at 3am after 12hrs, they're not as keen to take-off at 3am for a 12hr flight.
3) Regional specifics: in some places, night is actually the busiest time - in Middle East (like Dubai, etc) for example there is lots of flights coming and leavinigg in the middle of the night and it does not seem to bother anyone. I think it should be considered
That's one of those "nice to have" things that's really pretty hard to code. There's always a certain willingness for a percentage of the population to fly at "bad" times; it's difficult to really draw a mathematical model around perceived cultural differences on opinions of those. We can't even get seasonality of demand to tourist destinations -- something far more objective and more important -- trying to get regional demand variations is quite a bit more difficult to do.