LHR delays
 

Guys,

Quick question for the london ATC'ers.

Lots of delays this morning operating into LHR, slots, EAT's whilst holding etc.

The code for the slots was weather related. However, it appeared ok , maybe just a bit breezy (15- 20 knots ish)

How does this affect the flow rate when the separation looked to be the normal 3 miles?

The 3,000ft wind this morning was 270/45ish knots ergo traffic going down the approach would have had a slower groundspeed than in lighter wind conditions and so it takes a longer time to get from say 15nm on final to touchdown.

If it takes longer for each aircraft to go down the approach then you'll get less of them down in any one hour period and so if the demand is significantly greater than the landing rate being achieved flow will need to be put on to regulate said demand. Does that make sense?

Strong headwinds at altitude kill the landing rate.

Groundspeed!

There's an echo in here...

As HD will love to remember, in the old days on LHR 23 (before SMF ;) and vortex wake separations) we used to pack 'em in 2 miles apart, otherwise we'd be there all day. And we could still cross tow-ers on the dual taxiways and shoot the gaps with landers on 28L. Fabulous fun! The separation of arrivals using time separation is long overdue. When are we going to be provided with the technology to be able to tell 'number 2' to 'follow the one ahead by two minutes' ? Follow my leader', pearls on a string, we can just click 'em with a mouse and just sit back and watch...........:hmm:

Thanks for that chaps... seems so obvious now you mention it !

Perhaps we should have offered 200 to 4D ;)

Wrong kind of wind is it?;)

Throw a dyce... Yes, but you wouldn't believe the number of airline pilots and airfield managers who simply cannot comprehend that simple fact. They rush about like headless chickens: "What's the reason for the delays?" "Why are we only landing 35 an hour?" "Can't you pack them tighter?" When a two-second glance at the anemometer (or FMS!) would answer the question.

HD

I think you'll find that most pilots think that it's ATC who aren't flexible enough on days such as yesterday. I was asked for 160kts from about 12 miles yesterday luchtime. WTF?

Why not 180 to say 6 miles then reduce to finals speed. As you say, a distance separation will give you slower flow rate UNLESS you keep the speed up to generate an equivalent groundspeed - so why do ATC slow you down earlier?

TB.....maybe you were following an AFR?:ugh:

It is not done willy nilly mate. Maybe it was a trainee.

One things for sure, it was done for a reason!

HD,
It's a pity some of the vortex separations couldn't be reduced when it's windy,to recover some of the lost space with slow groundspeeds.The odd few miles saved could help reduce delays.The vortices may disperse quicker in rougher conditions.Just a thought but feel free to shoot me down.:)

Alan

I accept that it was obviously done with a reason - if we hadn't been slowed down we would have got to about 3 miles (ilo 2.5nm) behind a medium (not AFR) - and we were a heavy :rolleyes: .

If I'm following an AFR or IB or AZ I always get that extra twitch factor re spacing and their 160 kts to 4nm being somehow diffferent to everyone elses. This was not the case yesterday.

My general point is that ATC seem very rigid in their application of speed reduction points which in strong headwind/low groundspeed conditions does result in lower than possible flow rates. Don't get me wrong here, LHR and LGW are the best around, but it could be better with a little science applied.

We HAVE to provide standard vortex separation WHATEVER the wind! It would be nice to have time-based separation just for those windy days but the regulators won't allow us to use it, or even define what would be acceptable. On a very windy day we could squeeze it very tight, as we used to do on RWY23, but I'm sure that some of the fly boys would be screaming about being too close. The next problem is just how do you achieve that separation, they've tried several approach sequencing tools for 'normal' weather but none of them have worked so far, so what chance is there for 'windy' days?

Nah, we'd probably just use the TCAS Traffic display to reduce speed without the need to bother ATC...

:ugh: :mad:

OK, well lets just get the TCAS to hold 80 seconds timing from the one ahead to achieve a rate of 45. It should be fine with types of same wake category....

Topofthestack,
Remind me which part of the Mats part 1 vortex separation rules allows 2.5 nm spacing.I thought it was 3nm minimum.So LL reduce vortex minima already to suit themselves?:rolleyes:

Dycey..... so two "lights" need three miles VORTEX in Scotland?

The 180 to 160 speed reduction is used to fine tune the spacing.

You sometimes need that small overtake just to reduce the spacing a touch, especially if doing 2.5nm (which the weather wasn't officially suitable for the other day, cloud too low).

If you wanted to do 180 to 4 then we'd probably need to be turning you on at 200 so that we still have that 20kt differential. But whatever speed you do down final it's important that everyone does exactly the same otherwise more capacity is wasted as distance has to be provided for someone wanting to go fast behind somone wanting to go slow.

We are pretty flexible at getting the maximum number of a/c down the approach, years of experience have taught us what will work and what will not.

Time based spacing is on the back burner. The algorithms that ran FAST are still around and I believe could be adapted to provide guidance in tis respect. Be careful what you wish for...

WF.

Alan M,
Don't remember too many Cessna's doing VFR circuits at LL.:p It would seem that 2.5nm vortex is the norm,in Southern Englandshire,between non lights on a nice day.OR is it?;)