Are you a plane spotting fan who can’t stop looking at the aircraft in the sky and keep tracking aircraft online? If this sounds like you, you probably have noticed that sometimes flights between the same destinations use very different routes. Do you know why?

Usually, when airlines plan flights, they choose the route between A and B that is the least time-consuming. The reason is simple: the shorter the distance, the less fuel is used, airlines save money. However, there are some factors affecting the choice of flight routes and why flights to the same directions take different routes.

Firstly, some of the airspace routes are so busy that they are called “highways”. Usually, during a high flying season air traffic gets crowded and dispatchers watch planes flying one after another on the same route. The dispatchers manage planes to ensure they manage to keep the distance of at least 5 km from each other.

Another reason why flight routes may be changed is because of weather conditions. Wind direction (headwind, tailwind or crosswind) affecting the flying aircraft or bad weather on the planned route may be the reason to change it.

Furthermore, the region is important too. In certain parts of the world, like the Himalayas, terrain clearance under various emergency scenarios must be taken in consideration when making a flight path.

Keep in mind, when a flight route is changed, flights are required to be within a certain distance from a suitable diversion airport at all times. Remember, engine failure is just one of the many emergencies when the aircraft needs to land before reaching the planned flight destination.

Moreover, there are some flight rerouting reasons that are not related to the flight itself or its climate conditions. The first stage of every flight is planning which is always followed by paperwork. The more countries an aircraft flies over, the more paperwork this requires, so airlines look not only for the shortest way but for the least number of countries to fly over, too.

Also, all airlines cost-conscious and tend to choose to spend less, thus they might change flight routes to fly over countries which have a lower tax rate for flights over it.