Aircraft contrails over Southern England

[sidkid]

Why do airliners which are flying very high suddenly change direction, by anything up to 90 degrees? Surely in these days of satnav etc they can fly point to point without deviating too much?

[dundurn]

In many cases they are flying in defined air traffic corridors which function just like roads. What you're seeing is exactly the same as watching a motorist coming to the end of the motorway and "hanging a left"

The other point to bear in mind is that all the time a plane is turning, it's in a bank as well. Makes the tea and coffee harder to pour if the wings aren't straight and level!

[Mortartube]

Many are in a stack waiting to be allocated a spot to land. Effectively they fly in big circles at a certain height that air traffic control tell them to maintain.

I live in Southern England and they stack over the Lewes/ Heathfield sort of general area for Gatwick.

But as the previous anser also says, they are governed by air corridors and take pre determined paths to their destination.

[Toureman]

If you can see the contrails they are flying at over 27000 ft so they are not in a stack to land as this happens at a much lower altitude.

When they turn it is because air traffic control has told them to to join a corridor to their destination.

[Clanad]

If I may... there are about 5 and sometimes 6 North Atlantic Crossing "Tracks" used by commercial airliners to cross either direction. The direction of traffic changes twice a day for west bound in the daylight hours and east bound in the evening/night. These tracks are well defined "highways" as several of the posters intimate. However, each of the tracks have an equally well defined entry and exit point. Although it's been a while since my last crossing as a pilot, the entry and exit points used to be over and just west of England or Ireland. So, even though an aircraft adheres to the track, on leaving or entering the track it may have to make a considerable adjustment to the heading it was originally on just to reach the entry/exit point...

[Clanad]

Additionally, for zacmaster... the majority of the long range navigation systems used by airlines today are satellite GPS based. There are still some older inertial nav systems still being used, but most are at least backed up by the GPS systems...

[shylock73]

Hey sidkid, I bet you wish you hadn`t asked now. You won`t sleep to-night trying to work out clanads answer.

[sidkid]

You're right Shylock - still thinking!!
Thanks to you all for your responses