Aguila

This is not the case, but in other similar cases, sometimes you just want to provide that flight, because you think it is important to have a connection with certain city, even if you don't get money. You can do it because your other flights are profitable.

As an example, some may want to have a flight to Pyongyang even if there is very little demand, just to challenge the political prejudges of the world. And, again, many players might not live in big cities, so they may also create awesome flights to their local airport, as they which there were in real life.

Honestly it's not realistic anyways, you can change the engine on aircraft but only with the same type. 

It's because the internal computers are set up for a certain profile (I guess you could say) and you'd have to reprogram all the computers to change to a different engine type. 

Then just add the cost of reprogramming the computers. I am sure this is possible, and at least the airplane's makers do it, as I have seen many videos of airplanes testing different motors.

To make it realistic, make it super expensive to change the motors, which anyway I am sure are at least 1/4 of the total cost of the aircraft, and make the aircraft to be unusable for a week.

I'm not... with all respect, AE is terrible, severely outdated and extremely lacking in features and complexity.

Well, you say that because players do not require a complex computer like the one you built to play!

And as I said already i another thread, you need to limit the configs to realistic values. It's just too easy to make money with a 747 in 14F 60C 540Y. 

Well, in real life it is easy too, the hard part is to get the 747 and the route authorization!

I hope we could build new airports with something like 20 thousand millions or something similar, so people would save money to make the new airports.