Marcalorian

Maybe It could be a scaling effect; for instance, if you have up to 20 routes, you take a hit of 10-20% of your revenue, but if you have more than that you take 30-50%. Also, instead of being a huge event out of nowhere, there could be some warnings before hand, and let the player decide if he wants to continue investing, or save for the rough times ahead. I should have said that this is a mechanic that already exists in other games, like airtycoon online. There's pre-defined events that trigger the skyrocketing of fuel prices, or market crashes, and there's no way of surviving without re-defining your routes. In fact, it presents an opportunity to smaller companies, because the bigger companies are forced to sell their aircraft, so there's tons of aircraft available at low prices in the used market. That could help with the hardest part of starting you airline, which is building a fleet.

I don't know if this exists already, or if it's already planned, but there could be Recession/economic boom periods; maybe based on real events, like market crashes, oil prices rising, or just random events to increase the challenge. That's a good way to make sure the game isn't just about opening routes, players will be forced to make a decision as to which routes to keep.