London Airports' Holding Times: Thresholds?
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London Airports' Holding Times: Thresholds?
Hi - I'm an undergraduate engineering student working on some software designed to model the expected delay resultant from various factors of airport operations at Heathrow, Gatwick, Stansted and Luton. One of the essential factors is stacking or holding above airports on arrival; from experience, is there any typical "maximum holding time" (i.e. maximum average time that an aircraft is currently spending in a holding pattern) at which measures will be taken by air traffic control to ensure that the stack doesn't grow any larger? Possibilities may include delaying incoming flights, diverting flights (although I'm guessing this is extremely rare).
Thank you for your help in this - my research thus far has been less than fruitful.
Thank you for your help in this - my research thus far has been less than fruitful.
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1. ATC cannot divert flights; that is soley the pilot's responsibility. However, if an airport authority decides that for some reason it does not want the aircraft to land, ATC may be requested to send a message to that effect. However, it's still up to the pilot.
2. The length of time aircraft are in the hold can vary enormously - maybe from 2-3 minutes right up to an hour or more. In many cases, it is not the length of time aircraft are holding which causes problems but the number in the stack. In busy terminal areas the upper levels in holding areas may not be separated from adjacent routes. Therefore, if it is expected that aircraft may be require to hold so long that the upper levels would become occupied, the aircraft which would occupy those levels will be held at high levels outside the terminal area.
There are many other factors to be considered, but that may help.
2. The length of time aircraft are in the hold can vary enormously - maybe from 2-3 minutes right up to an hour or more. In many cases, it is not the length of time aircraft are holding which causes problems but the number in the stack. In busy terminal areas the upper levels in holding areas may not be separated from adjacent routes. Therefore, if it is expected that aircraft may be require to hold so long that the upper levels would become occupied, the aircraft which would occupy those levels will be held at high levels outside the terminal area.
There are many other factors to be considered, but that may help.
Aircraft inbound to the London TMA (Terminal Manouvering Area) are recommended to have 30 mins. holding fuel on any normal day.
Sometimes, due to weather factors, this is increased.
Also Aircraft can be held at the point of departure if there is too much traffic.
On Tuesday last week we had 45 mins. holding fuel and a 2 hour slot delay from Milan Malpensa to Heathrow, due to thunderstorms in the london area.
We actually departed only 1 hour late, and only did about 5 mins. holding as the weather had improved.
Hope this helps.
Sometimes, due to weather factors, this is increased.
Also Aircraft can be held at the point of departure if there is too much traffic.
On Tuesday last week we had 45 mins. holding fuel and a 2 hour slot delay from Milan Malpensa to Heathrow, due to thunderstorms in the london area.
We actually departed only 1 hour late, and only did about 5 mins. holding as the weather had improved.
Hope this helps.
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Thank you - that's exactly what I was looking for. Given what you've said about the relative importance of certain factors, I'll try to model some sensitivity regarding the stack size as well.
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Quite right, BOAC ... the recent AIC P 045/2009 equates "No delay expected" with not greater than 20 mins holding.
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S.D.E.
Another factor that you may consider is the policy of the relevant Airport Authority. It may allocate landing slots in such a way as to reduce the necessity to hold, or it may allocate more landing slots to increase capacity and/or satisfy demand.
In a way it kind of suits Air Traffic Control to have a ready and varied supply of aircraft to pull from the holding stacks in such order as to maximise runway utilisation efficiency by applying optimum wake separation spacing.
I just feed traffic into the London terminal area and watch with utter amazement as my Heathrow colleagues pack them in.
If you want more detail, perhaps one of our Approach buddies could help....but you need to clarify what level of knowledge you have already, so that any answer will be meaningful.
P.S. If the stacks are getting full, terminal control will ask the en route feed sectors to slow inbound traffic....we do it every day....quite normal....and it saves gas. If the stacks are full we can hold further out and at a higher more economical level......saving more gas.
In a way it kind of suits Air Traffic Control to have a ready and varied supply of aircraft to pull from the holding stacks in such order as to maximise runway utilisation efficiency by applying optimum wake separation spacing.
I just feed traffic into the London terminal area and watch with utter amazement as my Heathrow colleagues pack them in.
If you want more detail, perhaps one of our Approach buddies could help....but you need to clarify what level of knowledge you have already, so that any answer will be meaningful.
P.S. If the stacks are getting full, terminal control will ask the en route feed sectors to slow inbound traffic....we do it every day....quite normal....and it saves gas. If the stacks are full we can hold further out and at a higher more economical level......saving more gas.
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<<I just feed traffic into the London terminal area and watch with utter amazement as my Heathrow colleagues pack them in.>>
055166K... Ah, yes, but you have to accept that they are Superhumans with incredible skill, unknown in ordinary mortals. I came to earth alongside Superman. It was a toss up who would be a Heathrow Controller..... and he lost!
And if you believe that, you'll believe anything!!
055166K... Ah, yes, but you have to accept that they are Superhumans with incredible skill, unknown in ordinary mortals. I came to earth alongside Superman. It was a toss up who would be a Heathrow Controller..... and he lost!
And if you believe that, you'll believe anything!!
