Another question about track miles.

[FLCH]

Hi I fly into the UK very frequently from across the pond.Generally on approach I will ask the director if he/she could tell me the track miles to run, this will give me an idea of how to plan my approach. I would like to know with this distance given to me, should I plan my descent at a constant rate, or does it not matter if I end up milling around at a particular altitude early ? The only reason why I ask is a check airman bought up the subject, and said especially going into LGW that we should fly a constant rate for noise considerations. Is this true and is this applicable to all operations into UK airports ? My humblest apologies if this has been beaten to death before.

[TopBunk]

FLCH
Generally on approach I will ask the director if he/she could tell me the track miles to run, this will give me an idea of how to plan my approach

They will usually (99%) of the time give you the track miles with descent to an altitude (from a FL).

It has been covered before, but when descending on QNH, the min RoD of 500fpm does not apply within the London TMA (therefore into LHR, LGW, STN). The prefered method to minimise noise levels is to achieve a continuous descent (CDA), ie without a level segment if at all possible. Obviously this is not always possible, but I know that at LHR it is measured for all operators. Not surprisingly home operators with the greatest local knowledge fare best with BA at 94% CDA followed closely by BMI, VS and EI (locals really!)

HTH

Edited to stress what is wanted is a Continuous Descent and not necessarily a Constant Rate.

[FLCH]

Thanks very much Top Bunk ! I'll spread the word......

[sidtheesexist]

They monitor them into LGW too with stats published periodically. I too have a question and apologies if already answered elsewhere, but the how does the controller obtain the distance? Pray tell and no crystal ball type answers please.

[Del Prado]

but the how does the controller obtain the distance?

by adding up the spacing requirement between each inbound and adding a bit extra for the 'catch up' (as aircraft slow from from 210-160kts)
e.g You are number 4, no.2 is at 10 miles 2x six mile gaps plus a couple for the catch up, you are 14 miles behind no.2 or 24 miles from touchdown.

If the spacing is minimum vortex (ie no departure gaps required) a good rule of thumb is to add up in fives e.g you are no.5, no.2 is at ten miles therefore you have 25 miles from touchdown.

In light traffic conditions an approximation of the intended track is used.
e.g passing abeam the field, you may have a 12 mile downwind, 4 mile base leg and an 8 mile final or 24 miles from touchdown.

Hope that's clear enough, it's always a 'best guess' but they are surprisingly accurate.

Out of interest, do you always get told your track miles at Gatwick ?

[sidtheesexist]

Del prado - thanks for your explanation. Re LGW - from my experience they (ATC) usually slip the track miles in somwhere along the line. Forgive me if I'm being thick but doesn't your explanation assume that all ac on a particular inbound route (when picked off for vectors) are following near as dammit the same track? Cheers.

[Del Prado]

doesn't your explanation assume that all ac on a particular inbound route (when picked off for vectors) are following near as dammit the same track?

I tried to explain two scenarios-light traffic and when you are part of a sequence.

In light traffic (ie you are number 1) I think/hope it's self explanatory.


When you are part of a sequence and lets say the spacing required by the tower is 6 miles then you will always be 10 miles from touchdown as the preceding passes 4 dme.
If you are number 3, you will be 16 miles from touchdown when number 2 is at 10 miles

Now imagine you are number 4 and number 3 is on a straight in at 16dme, you have 22 miles from touchdown.
But if, for example, you are downwind just passing abeam the field and will eventually get an eight mile final, you still have 22 miles from touchdown but you are not going to follow the track of Number 3 (at least not until you turn finals).

By the same principal, no matter the tracks the aircraft take, you will always be 6 miles behind the preceding who will be 6 miles behind the one in front of them. It's just a question of knowing your 6 times table.

Another example - You could arrive at TIMBA at the same time as a company aircraft. If you are number 8 and he is number 9, you might have 46 miles from touchdown, then he has 52.
I could vector you across towards WILLO then give you a long downwind and long final to use up the 46 miles.
Your company aircraft could sit in the hold for 1 pattern (which uses up 20 miles) then get more of a standard circuit for the other 32 miles. You have not followed the same tracks but the track distances are correct.

Finally, we have to take into account the 'catch up' as aircraft slow from 220kts to 160. If you are going along the motorway at 70 and you come to a 50 limit, the distance to the car in front reduces as it slows down before you.
If you are 6 miles behind number 1, both at 220kts, he will slow earlier than you and the 6 mile gap will erode therefore we add a couple of extra miles to the track distance to take this into account. In the examples above I've disregarded the extra miles for the catch up in the interests of clarity !

I think I've managed to make a simple concept seem incredibly complex but I hope this helps. feel free to ask me to clarify anything (or pick holes in my explanation !)

[sidtheesexist]

Del Prado - many thanks for your detailed explanation. Being a bear of little brain I'll prob have to re-read your informative post a couple of times but I think the semblance of an understanding is forming! Cheers. Sid