Everyone who regularly flies by plane, for example, on vacation abroad, sooner or later may find himself in a situation where the passenger board, for one reason or another, must make an emergency landing. However, even in this case, the plane will not be on the ground immediately. If the situation is not critical, then the liner will circle over the landing site for a long time. Question: why?
The most obvious answer that suggests itself is an air burst. Even for a plane making an emergency landing right now, there may simply not be a place, although the dispatchers will try to let such a board pass as quickly as possible. In reality, the point is not at all in some queues, but in the degree of filling of the fuel bank.
The fact is that aircraft have different takeoff and landing weights. Takeoff and landing are the most difficult and at the same time dangerous moments of the flight. The laws of physics and the design features of aircraft are such that the landing weight of the machine must always be lower than the takeoff weight. Why? Because the force of gravity acts on the plane. Landing is always harder than taking off. So planes take off with a conditional "overload". Before landing, the excess mass is removed due to the fact that the fuel burns out during the flight!
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Thus, if the aircraft has to make an emergency landing, it may not have time to use up the amount of fuel required for its landing weight to reach an acceptable level. If the situation is not critical, then the controller will force the pilots to burn as much fuel as possible in order to make the landing safer.
Some will ask: why can't the fuel just be dumped?! Surely many have even seen videos or photos of how planes do it. In fact, everything is simple. Firstly, anyhow where it is impossible to dump fuel. Secondly, most popular models of passenger liners, such as the Boeing-737 and Airbus-320, are simply not equipped with such a mechanism. So you have to either take risks or circle in place.
In continuation of the topic, read about 7 largest turboprop aircraft in the history of mankind.
Source: https://novate.ru/blogs/300322/62529/