Keeping the tarmac in sight

[allen ives]

From here (in north London) you can watch planes taking off from Heathrow. Over the years, I have noticed that jumbos heading east or north ALWAYS follow the North Circular to the M1 junction, then effectively turn left up the M1. The vast majority of smaller planes which achieve height more quickly follow the M4 for a while, then hang a left wherever they are, and head off across the suburbs. It seems that pilots like to keep an emergency landing area in hand until they get to about 5,000 feet. Can anyone in the know confirm whether this is true or not?

[incitatus]

If you think about it you know this isnt so. The streetlights would cause worse damage than just landing in a field. The flightpaths are largely fortuitous, but as London is largely radial in nature and planes navigate using polar coords. it is inevitable that some shadowing would occur. Perhaps the flightpaths date back to the days when they really did follow the roads, for navigation purposes.

[allen ives]

Thanks for the thoughts, Inkie, but as someone once said, 'And yet it moves'. Go and sit on a hill in NW London and watch the planes. Jumbos always follow the route, smaller planes do not - and for much of NW and W London, it ain't a choice between fields and tarmac. It's houses or tarmac...

[incitatus]

The houses would be softer to land on. Also think on yourself. Light aircraft are not permitted to use commercial routes around heathrow as it is too busy....

[incitatus]

It was Galileo, wasn't it?

[allen ives]

Yes it was Gallileo. After all the wisest men of the age had demonstrated conclusively that the earth did NOT move, and was the centre of the universe, Gallileo recanted his heretical sun-centred views. But he was heard to mutter 'And yet it moves'.

[allen ives]

Sorry, Inkie, I didn't make myself clear enough. I'm not talking about jumbo jets as opposed to Cesna-type light aircraft, I'm talking about jumbo jets as opposed to ALL other passenger jets, i.e. with no upstairs, and only two (or sometimes four) engines. I repeat, go and sit on a hill. Try Jubilee Park in Kingsbury, from where you can see the North Circular, Staples Corner flyover, and the start of the M1. Watch as jumbo after jumbo comes along the North Circ then turns up the M1. And notice all the other passenger jets flying at much higher altitudes over Greenford, Wembley, Kingsbury, etc., on their way north or north east. And then tell me again that it doesn't move....

[incitatus]

Theologians had proved the world flat. Wisdom and theology rarely go hand in hand..... Mind you had Mr Galilei kept his gob shut, he could have made it to England and avoided a lifetime in the slammer. Interesting to note that the phraseology that the RC church wanted from Galileo about astronomy is the same as that insited on by many US states about evolution.....

[allen ives]

Inkie old chum, never mind about Mr.G. I'm still looking for an explanation of the jumbo/ordinary jet phenomenon which I expanded above. If you don't fancy that, kindly repair to Food and Drink and answer my question about High-rise Bread. And I still haven't had a sensible answer to the Riddle question....

[incitatus]

OK then. Motorways are not viable landing strips, so put this to one side. The differentiation between jets is a matter of route booking and destination. Each destination has a limited number of flight paths, which are rigidly defined for traffic control reasons. Long haul flights take priority, and so the most direct routes will be booked for the largst planes. I dont think theres much of a mystery here. Now back to the routes following roads thing. I still think its due to the radial nature of London, rather than anything else. When flying point to point planes do not navigate in straight lines, as the surface of the earth is non-euclidean. Instead they use Great Circles, which appear curved from the ground. This may explain your M1 dogleg. Remember also that around heathrow there is a massive holding pattern of spiralling planes, both inward and outward, which extends for 50 miles or so. A good place to observe this is the bridge over the Serpentine. The turning circles of large planes tend to be bigger than small ones, so even if travelling in the same direction the large ones will turn much later, and further out.

[allen ives]

Okay then, certainly getting close. I'm off back up Kingsbury Hill with binoculars and notepad, and will report back. (Matey? Very Inspector Morse).