How about splitting the Economy demand for a flight into a further 3 categories. High fare, medium fare and low fare. I think this could improve the realism of the game modelling the kind of demand that is seen worldwide. Flights between buisness centres and large cities would have people willing to pay more for an economy ticket than they would for a holiday destination so have a high, high fare demand. Also in poorer continents like Africa there are a lot of people, but few can afford to fly so this could be modelled with a very high low fare demand but a really small high fare demand.
I understand i haven't explained it as clearly as i could have done
hope you understand