why the zig zag approach over tower bridge then waterloo bridge into heathrow?

[The Lone Gunman]

A lot depends where you come in from, but the busiest is the stuff coming in from the Dover approach and down the Thames.

Arriving traffic is peeled off the approaches and put in holding patterns at (I think) 4 control centres. The big left puts you under Biggin Hill control.

The big right then puts back on approach to Heathrow and allows the other stacks to merge in.

If it was busy traffic then you would continue in the Biggin holding pattern untill a place came available so would probably keep doing lots of lefts.

It only appears a a zig zag because Heathrow approach is so good that you are out of the holding pattern and on approach almost immediately.

Please forgive any innacuracies, this is from memory from working with Air Traffic Management at Eurocontrol and talking to ops.

[chef]

http://avsim.com/geoffschool/combined/HeathrowSTARs.htm

maybe some help

or this

[chef]

"The zig-zag is to permit traffic to be sequenced into the "circuit". A similar procedure exists off BIG to the south. When things are quiet LAM traffic can leave the VOR on a SW track for a straight-in on westerlies. On easterlies traffic which would be going round in the hold on westerlies can be on the downwind leg for the 09s. Track distances from LAM are around 35+ miles on westerlies and 50+ miles on easterlies but there is more room on easterlies to have more off LAM all at the same FL and 3nm apart."

whatever that means

source

[hyperD]

Zig-a-zig Aaaaaahhhhh

I'm assuming this is when you come off the stack and to intercept the ILS for runway 27L or R. There are 4 holding points (stacks) for Heathrow - Ockham, Biggin Hill, Bovingdon and Lambourne. Lambourne STAR shows a left turn coming off the stack followed by a right turn to intercept the ILS on 27R.

More on the Initial Approach Procedures (w/o Radar Control) here

Otherwise could just be traffic positioning. Difficult to say really.

[hyperD]

Many years ago, I practised the racetrack holding pattern on the CIT NDB at Cranfield for my instrument rating. I'll have to dig out the old charts...

[xoggoth]

These things are done in order to annoy as many people as possible. Most of the large corporate and public sector budgets are spent on research in order to maximise annoyance among the general public.

[MPwannadecentincome]

http://avsim.com/geoffschool/combined/HeathrowSTARs.htm

maybe some help

or this

Ah so I was in Lambourne and its an S shape - I don't remember going quite as far as the M1 though, I think it was a much smaller S - maybe due to lighter air traffic at that time.

I've noticed even if there is no stack the approach still does a tight S.

[MPwannadecentincome]

"The zig-zag is to permit traffic to be sequenced into the "circuit". A similar procedure exists off BIG to the south. When things are quiet LAM traffic can leave the VOR on a SW track for a straight-in on westerlies. On easterlies traffic which would be going round in the hold on westerlies can be on the downwind leg for the 09s. Track distances from LAM are around 35+ miles on westerlies and 50+ miles on easterlies but there is more room on easterlies to have more off LAM all at the same FL and 3nm apart."

whatever that means

source

When we entered the Lambourne stack the map display said we were approx 35 miles from destination, during the S manouvre I think it was about 20 miles

[centurian]

I often wonder when flying into Heathrow, what is this zig zag left hard turn

Making sure the hydralics still work

[Flubster]

Isn't it to make terrorist ground-to-air missile attempts a bit trickier?