Holding patterns -why?
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Holding patterns -why?
Hi all...another stupid question....why do planes circle in holding patterns before landing? With modern computers etc, can't they land right away (subject to, say, bad weather over the airport etc)?
Also, how much does it cost to do an orbit in, say, 737 or A380?
Also, how much does it cost to do an orbit in, say, 737 or A380?
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Do you have a particular airport in mind?
Certainly in my part of the World ( Ireland, north and south ) holding patterns are exceptionally rare and only occur due to weather or an incident on the runway or taxiway. Most aircraft are cleared straight-in with only an occasional dog-leg to slot them in behind others on approach.
Edit: I note you're from London. Heathrow holding patterns... now there's a mess resulting from congestion. Not only aircraft waiting for their slot but also ATC arranging aircraft approaches by wake-category, so that an E-170 doesn't end-up behind an A380.
The alternative, such as practised within the USA, is to hold aircraft on the ground at departure airport so that there is less holding at destination. But that doesn't work across ATC regions and is really just another hack around the fact that we don't have free-flight navigation, by which method all aircraft would arrive exactly on time every time.
Certainly in my part of the World ( Ireland, north and south ) holding patterns are exceptionally rare and only occur due to weather or an incident on the runway or taxiway. Most aircraft are cleared straight-in with only an occasional dog-leg to slot them in behind others on approach.
Edit: I note you're from London. Heathrow holding patterns... now there's a mess resulting from congestion. Not only aircraft waiting for their slot but also ATC arranging aircraft approaches by wake-category, so that an E-170 doesn't end-up behind an A380.
The alternative, such as practised within the USA, is to hold aircraft on the ground at departure airport so that there is less holding at destination. But that doesn't work across ATC regions and is really just another hack around the fact that we don't have free-flight navigation, by which method all aircraft would arrive exactly on time every time.
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Aircraft are already Held on the ground due to congestion, it's Done through slots. Different system maybe than the us but same principle.
The Heathrow Holds are an effect of it being extremely congested, you will find the same at other places but not constantly in use like at Heathrow
The Heathrow Holds are an effect of it being extremely congested, you will find the same at other places but not constantly in use like at Heathrow
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Yes, El Bunto...I was thinking of Heathrow....on a 50 min flight from Lux, we would spend maybe 10 mins going round in circles....
Not being a commercial pilot, I thought maybe planes could slow down/ speed up in flight slightly, to coincide with a straight in approach and landing. Seems like a huge waste of fuel just going round in circles...though I don't know how much fuel is wasted by this
Not being a commercial pilot, I thought maybe planes could slow down/ speed up in flight slightly, to coincide with a straight in approach and landing. Seems like a huge waste of fuel just going round in circles...though I don't know how much fuel is wasted by this
Heathrow holding patterns... now there's a mess resulting from congestion.
The other way would be to understand that, for many years until recently, using holding stacks was the only way to guarantee a sustained landing rate at the level that Heathrow achieves. The stacks may eventually become redundant, but for the time being they are a legacy of how things have always been.
It's not rocket science, just basic queuing theory.
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dkatwa... have a look at this web site and it will give you some idea of the amount of traffic in the skies. Flightradar24.com - Live flight tracker!
dkatwa
As HD's link will show you Heathrow has four stacks:
Bovingdon NW
Ockham - SW
Biggin - SE
Lambourne - NE
Routing via those points is usual, even if there's no need to actually enter the holding pattern. Probably the only practical way to meet need to separate LHR inbound from outbound and both from traffic using the other London airfields as well as providing a clear starting point to sequence them onto approach respecting wake turbulence etc issues.
As HD's link will show you Heathrow has four stacks:
Bovingdon NW
Ockham - SW
Biggin - SE
Lambourne - NE
Routing via those points is usual, even if there's no need to actually enter the holding pattern. Probably the only practical way to meet need to separate LHR inbound from outbound and both from traffic using the other London airfields as well as providing a clear starting point to sequence them onto approach respecting wake turbulence etc issues.
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Aircraft are already sped up and slowed down to manage the holds and reduce the holding times, here's an article on slowing down inbounds
Cross Border Arrival Management (XMAN) Trial | NATS
With regards to the cost I'll leave it to one of the pilots to answer in detail, but a full hold is 4 minutes flying time.
Also if you're in the hold 10 minutes you're unfortunate, the average in June 2014 according to the article above was 8 minutes, I think it's reduced even further now with xman although I'm not sure what the latest figure is.
Also remember that Heathrow is so busy that if you start missing landing rates you will have delays and/or cancellations later. Heathrow needs to consistently land at aircraft the entire day, if they don't it will cause issues later, which is down purely to mathematics really. That's how full Heathrow is in terms of capacity.
Cross Border Arrival Management (XMAN) Trial | NATS
With regards to the cost I'll leave it to one of the pilots to answer in detail, but a full hold is 4 minutes flying time.
Also if you're in the hold 10 minutes you're unfortunate, the average in June 2014 according to the article above was 8 minutes, I think it's reduced even further now with xman although I'm not sure what the latest figure is.
Also remember that Heathrow is so busy that if you start missing landing rates you will have delays and/or cancellations later. Heathrow needs to consistently land at aircraft the entire day, if they don't it will cause issues later, which is down purely to mathematics really. That's how full Heathrow is in terms of capacity.
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Many years ago I frequently flew as SLF to LHR, but hardly ever landed in the morning rush hours without first being stacked above the green and pleasant land in the Home Counties or thereabouts!
One of the few exceptions was a fuel emergency in B-747! I still remember the eerie approach we made from the Channel Coast and the sighs of relief at touch-down!
I think I'll prefer a couple of turns in the stack any time!
One of the few exceptions was a fuel emergency in B-747! I still remember the eerie approach we made from the Channel Coast and the sighs of relief at touch-down!
I think I'll prefer a couple of turns in the stack any time!
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Originally Posted by DaveReidUK
It's not rocket science, just basic queuing theory
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Crazy Voyager, not sure why you think the average hold reflects what you should expect. It all depends on the time of day and, more importantly the crosswind which, in my experience of over 50 years of flying into the Row, has become more prevalent in recent years and, of course, runway 23 has long gone.
Using the first flight out of Shannon to Heathrow which used to be at 07.30 we would regularly be held at Shannon waiting for a slot release. Best departure was 07.55, worst was 08.35. On the 08.35 departure with an in air time scheduled at one hour we actually touched down at 10.15 with a slow crossing and a hold of over 30 minutes. Reason cross wind.
The flight has now been rescheduled for 08.45 but we regularly still have a short on ground hold, a slow crossing and up to 15 minutes over the Surrey countryside.
Now you might think that an 11.25 scheduled arrival might fare better but coming in from Houston on the BA196 we often get a ten to fifteen minute hold. If the winds on the pond are favourable we can arrive over the UK coast up to forty minutes early only to be told by the flight deck that we have been asked to slow and then we get in the hold.
It gets worse, having landed we often have a ten to twenty minute ride around the Heathrow concrete before we can get on a gate.
Using the first flight out of Shannon to Heathrow which used to be at 07.30 we would regularly be held at Shannon waiting for a slot release. Best departure was 07.55, worst was 08.35. On the 08.35 departure with an in air time scheduled at one hour we actually touched down at 10.15 with a slow crossing and a hold of over 30 minutes. Reason cross wind.
The flight has now been rescheduled for 08.45 but we regularly still have a short on ground hold, a slow crossing and up to 15 minutes over the Surrey countryside.
Now you might think that an 11.25 scheduled arrival might fare better but coming in from Houston on the BA196 we often get a ten to fifteen minute hold. If the winds on the pond are favourable we can arrive over the UK coast up to forty minutes early only to be told by the flight deck that we have been asked to slow and then we get in the hold.
It gets worse, having landed we often have a ten to twenty minute ride around the Heathrow concrete before we can get on a gate.
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Sure, you will sometimes have holds over the average. But the pure mathematics are that if say flight A holds for 15 minutes, then flight B holds for 7 minutes, creating an average of 8. Obvously you need to apply this to all the inbounds, but roughly 50% of the time you should hold less than the avergage time. Therefore my comment that to hold more than 2minutes over the average could be seen as "bad luck". Obviously as you say yourself, in periods of high inbound demand hold times are incraesed, so if you reduce the time scale from the entire day the statistics change. In the morning the average hold might very well be more, say 12 minutes (just a figure with no facts to base it on), but then the hold time during some other tmie of the day will be less, to once again create the 8 minute average.
Also on days with delay the hold times are often increased, part of this is because it seems most airlines rather depart and then hold for extended periods rather than sit on the ground. Why I don't know but if we ever get the option to ask someone "do you want to go now and hold for 30 mintues plus or wait half an hour" they always seem to pick the option of going now. Why I don't know (airline policy?)
Also on days with delay the hold times are often increased, part of this is because it seems most airlines rather depart and then hold for extended periods rather than sit on the ground. Why I don't know but if we ever get the option to ask someone "do you want to go now and hold for 30 mintues plus or wait half an hour" they always seem to pick the option of going now. Why I don't know (airline policy?)
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Of course the statistics are there but we all know there are lies, damned lies and statistics and averages only work if your situation is average or better. For passengers travelling at peak times the delays seem to be getting worse.
Whilst traffic has obviously increased since my first flight into LHR in 1963, the increase in hold times, the number of in flight slow downs and the number of pre take off on ground holds on a number of routes seems to have increased at an accelerating rate in the last few years.
The use of one runway for take off, the other for landing, has stymied the reduction in delays for years. Having had professional contact with the CAA and NATs for many years I know the "reason" but can point to many airports around the world where runways with similar proximities work in parallel for landing safely and satisfactorily.
The reason for going and having to hold on arrival stems, it seems, from the FAA's edict that if you are off the gate on time, it doesn't matter how long it takes to make the runway, or if you have to hold at the destination, your flight will be logged as departed on time. This seems to have become a world wide norm.
Whilst traffic has obviously increased since my first flight into LHR in 1963, the increase in hold times, the number of in flight slow downs and the number of pre take off on ground holds on a number of routes seems to have increased at an accelerating rate in the last few years.
The use of one runway for take off, the other for landing, has stymied the reduction in delays for years. Having had professional contact with the CAA and NATs for many years I know the "reason" but can point to many airports around the world where runways with similar proximities work in parallel for landing safely and satisfactorily.
The reason for going and having to hold on arrival stems, it seems, from the FAA's edict that if you are off the gate on time, it doesn't matter how long it takes to make the runway, or if you have to hold at the destination, your flight will be logged as departed on time. This seems to have become a world wide norm.
Last edited by philbky; 7th Feb 2015 at 21:05.
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Sure, you will sometimes have holds over the average. But the pure mathematics are that if say flight A holds for 15 minutes, then flight B holds for 7 minutes, creating an average of 8.
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Oops, maybe that's what I get for dropping out of uni and starting work in aviation instead 
Not sure how I managed to come to that conclusion since it's obviosuly wrong but might as well leave it there now for the internet to laugh at.
Hopefully though the rest of the post makes some sort of sense? Yes I'm aware it's a slightly blunt statistic, but at the end of the day, if the average delay is 8 minutes a random flight at a random time will have a delay of roughly that and a hold of more could be seen as "bad luck".
Anyhow, might be time to move on.
I think though, philkby, that you touch on a very interesting and good point. To measure on time performance the way it's done now does create some very "interesting" results, as you said yourself, lies, damned lies and statistics.
Not sure how I managed to come to that conclusion since it's obviosuly wrong but might as well leave it there now for the internet to laugh at. Hopefully though the rest of the post makes some sort of sense? Yes I'm aware it's a slightly blunt statistic, but at the end of the day, if the average delay is 8 minutes a random flight at a random time will have a delay of roughly that and a hold of more could be seen as "bad luck".
Anyhow, might be time to move on.
I think though, philkby, that you touch on a very interesting and good point. To measure on time performance the way it's done now does create some very "interesting" results, as you said yourself, lies, damned lies and statistics.
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<<If one flight has a hold of 15 minutes, and another 8, the average hold time of the two is (15+7)/2=11 minutes, not 8............>>
That still baffles me, but I never was much good at maths! 15 and 8 suddenly become 15+7...?
That still baffles me, but I never was much good at maths! 15 and 8 suddenly become 15+7...?
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dkatwa
First, the terminology. Planes don't circle, the patterns are "racetrack"
Another thing that can result in holding is the weather. Down my way if a line of thunderstorms hits the airport, numerous things can occur. There may be a need to change runways and aircraft will be requesting vectors clear of cells. This makes it very busy in the terminal area so arriving aircraft outside the terminal area mal be placed in outer holding stacks. When thunderstorms are in the area, ground staff are not permitted out on the aprons (WHS requirement) so aircraft cannot park.
Similar to above, a fast moving front may require a runway change. A tower tries to stay ahead of the change but sometimes they get caught by the speed.
Rapidly deteriorating weather below the CAI I ILS minima can also cause problems. Greater spacing is required between approved CAT II and CAT III aircraft and if there are any CAT I one aircraft in the mix, they have to be put somewhere.
Another thing that can result in holding is the weather. Down my way if a line of thunderstorms hits the airport, numerous things can occur. There may be a need to change runways and aircraft will be requesting vectors clear of cells. This makes it very busy in the terminal area so arriving aircraft outside the terminal area mal be placed in outer holding stacks. When thunderstorms are in the area, ground staff are not permitted out on the aprons (WHS requirement) so aircraft cannot park.
Similar to above, a fast moving front may require a runway change. A tower tries to stay ahead of the change but sometimes they get caught by the speed.
Rapidly deteriorating weather below the CAI I ILS minima can also cause problems. Greater spacing is required between approved CAT II and CAT III aircraft and if there are any CAT I one aircraft in the mix, they have to be put somewhere.