How dangerous is a single runway, major airport?

[RHPrague]

This is in connection with Prague’ s desire to build a new parallel runway to the main one with trajectory 6/24. Actually it has a 2nd runway on trajectory 12/30, which it would close.
Its proponents are now pushing the safety aspect, that a single runway airport is dangerous in the event of an emergency? My question is, how dangerous? Safety is never 100% of course. I cannot recall an incident at a comparable European airport with a single runway which was blamed on the lack of a 2nd runway But I could well be wrong.

All thoughts and education appreciated!

[FlyingStone]

It isn't. Mutliple runways are primarly used to increase capacity, not for the odd case every 50 years when the only runway is blocked and there is an aircraft that has an emergency. Prague is situated in the center of Europe with tons of airports around, where aircraft can easily and safely divert, should the single runway be closed.

Worth mentioning is that even if you have 2 or 3 runways, if a runway becomes closed due to emergency (let's say an aircraft on fire), there would likely be no landings on the other runway(s) due to insufficient fire and rescue coverage.

[RHPrague]

Thank you! This is what I supposed, but it's great to have it confirmed by people who know what they are talking about. If anyone else would like to add anything it would be appreciated, even if only to support the view above.

[spekesoftly]

Gatwick's second runway, built in the 1980s, is an exception. It cannot be used to increase capacity (at present!) because it is too close to the original southern runway for simultaneous use, but can be brought into to use during periods of maintenance or an incident blocking 26L/08R.

[sandiego89]

There can be some safety arguments made, especially with separating traffic- better staggering arrivals and departures for example, but a second, parallel, runway could also increase the threats of runway incursions with more cross runway taxis. Capacity and redundancy are the main drivers, but planners always like to list safety as a factor as it sounds better than "to make more money and have more flights"

[RHPrague]

Excellent, thank you!

[spitfirek5054]

Look at Kai Tak when it was open.

[RHPrague]

Thanks. I am actually British but living in Prague; but my Czech friends may well be interested to read it

[JENKINS]

The Royal Air Force, I believe relies on a single runway field in UK for its transport fleet. Their experts will, I imagine, have carried out a feasibility study.

[Bergerie1]

RHP,

Put simply, it is not dangerous in an way, only some different procedures required to maintain safety.

[RetiredBA/BY]

The Royal Air Force, I believe relies on a single runway field in UK for its transport fleet. Their experts will, I imagine, have carried out a feasibility study.
Brize is hardly a major airport !

....but in times of conflict a single unexpected bomb on the runway could ground the entire tanker and transport fleet. Brilliant.

[JENKINS]

Witness my Welsh cynicism, BA/BY.

[Musket90]

Single runway major airports are no more "dangerous" than multi-runway airports as long as procedures are adhered to. The main reasons for having more than one runway is capacity and business continuity, although how much capacity is gained will depend on the separation between the runways and their alignment. For example if used in segregated mode (one for departures, one for arrivals) and aircraft need to cross one runway to/from parking areas then this will affect capacity on the runway to be crossed.

Gatwick's northern runway was constructed purely for business continuity, so that if the main runway was closed for planned maintenance or blocked due to an unplanned disabled aircraft then they could continue to operate although not to the same capacity level as the main runway. The depletion of Fire Service cover in the event of an aircraft emergency or accident can delay the re-start of operations but at very busy airports with two runways or more which have more than one fire station there is the option to provided the appropriate level of fire cover at both so when one responds to the incident the other has the cover available allowing operations to re-start very quickly, although this would depend on the seriousness of the incident.

[spekesoftly]

and aircraft need to cross one runway to/from parking areas then this will affect capacity on the runway to be crossed.


Manchester being one such example, where all aircraft using the southern runway have to cross the northern runway.

[Cough]

One aspect that's advantageous when you've got multiple non intersecting runways is when you have some sort of destructive emergency on departure, say uncontained engine failure. Having left a trail of parts over the departure runway you can of course simply reland on the other runway. Now if it's truly a single runway airport, of course you can get it all picked up (once the hot parts are cool enough) and then you can land back. But there is a case if you've GOT to reland ASAP then multi runways are better.

[a5in_the_sim]

One aspect that's advantageous when you've got multiple non intersecting runways is when you have some sort of destructive emergency on departure, say uncontained engine failure. Having left a trail of parts over the departure runway you can of course simply reland on the other runway. Now if it's truly a single runway airport, of course you can get it all picked up (once the hot parts are cool enough) and then you can land back. But there is a case if you've GOT to reland ASAP then multi runways are better.

True but not significantly. Any parts trail would likely be quite far down the runway, commencing close to the point at which V1 was achieved on departure; otherwise I would have stopped. Personally I wouldn’t be at all discouraged from landing back on that runway if my aircraft was crippled, particularly if it was a time critical scenario. I would be confident of encountering that debris at a fairly low speed on landing.

It’s certainly the case that “safety” is becoming an overused reason for essentially commercial decisions. Conversely “safety” is conveniently forgotten when it obstructs commercial gain.

Weak regulation and oversight has shockingly emboldened the aviation industry.

[dixi188]

One aspect that's advantageous when you've got multiple non intersecting runways is when you have some sort of destructive emergency on departure, say uncontained engine failure. Having left a trail of parts over the departure runway you can of course simply reland on the other runway. Now if it's truly a single runway airport, of course you can get it all picked up (once the hot parts are cool enough) and then you can land back. But there is a case if you've GOT to reland ASAP then multi runways are better.
It happened at Gatwick about 1982. A Northwest 747 was shedding turbine blades on take-off. IIRC it diverted to Heathrow and it took quite a while to pick up all the debris. I think they did a "FOD Plod".

[DaveReidUK]

once the hot parts are cool enough

Which could take hours ... :O

[InSoMnIaC]

Gatwick's second runway, built in the 1980s, is an exception. It cannot be used to increase capacity (at present!) because it is too close to the original southern runway for simultaneous use, but can be brought into to use during periods of maintenance or an incident blocking 26L/08R.


I have no experience with Gatwick however I bet The second runway there can be used to increase capacity. At such airport where parallel rwys are too close to allow for simultaneous approaches, One is used for departure and other for arrivals. This increases capacity because it allows for one aircraft to line up while the other is still on approach. As the landing aircraft touches down, the departing aircraft can commence takeoff.

[awair]

LGW has , or at least used to have, the most efficient single-runway ops I have experienced.

Rapid Exits placed so a holding aircraft is released the moment the landing aircraft is clear.
Line up after the landing, gets you in position.
The next traffic is at 3? miles, and cleared to land as the departing rotates. The lander is around 200'.

Not so at MAN, where traffic didn't justify a 2nd runway. I don't think they ever came close to processing at half the rate of LGW.

No blame to ATC for the flow rates...

[staircase]

I gave this some thought when I was still flying, and I did wonder about arriving back at, say LGW or MAN (before the second runway was built) at peak periods, with management trying very hard to get us to carry ‘plog’ fuel.

My concern was that if the main drag was blocked then all would have to divert. But to where, given that Liverpool, our primary diversion would be very busy with the lowest cost carriers? Leeds would have very little capacity to offer and Doncaster had not yet opened. Much the same with LGW and the airfields there.

I reckoned there would have been some very tight ‘sphincters’.

[surely not]

I have no experience with Gatwick however I bet The second runway there can be used to increase capacity. At such airport where parallel rwys are too close to allow for simultaneous approaches, One is used for departure and other for arrivals. This increases capacity because it allows for one aircraft to line up while the other is still on approach. As the landing aircraft touches down, the departing aircraft can commence takeoff.

A little research before posting this would have removed the need for you to post the comment. Put plainly, that doesn't happen at LGW.

[Nimmer]

There are plans to use both runways at Gatwick. I am not sure how developed these plans are though. ATC procedures and spacing requirements will be a challenge.

[dixi188]

There are plans to use both runways at Gatwick. I am not sure how developed these plans are though. ATC procedures and spacing requirements will be a challenge.
The only way I could see that happening is to use 26L for take-off and 26R for landing. But I think the taxiway too is close to 26R. I suppose you could put a large holding area where the fire training is so a few aircraft could land and hold, and then all taxi in one behind the other while 26L was used.

[DaveReidUK]

The only way I could see that happening is to use 26L for take-off and 26R for landing. But I think the taxiway too is close to 26R. I suppose you could put a large holding area where the fire training is so a few aircraft could land and hold, and then all taxi in one behind the other while 26L was used.

No - 26R for takeoffs (narrowbodies only) and 26L for all landings is the plan, also involving some taxiway and stand realignment.

Lots of debate on the detailed workings here on PPRuNe when the plan was first unveiled about 2 years ago.

[WHBM]

It’s certainly the case that “safety” is becoming an overused reason for essentially commercial decisions. Conversely “safety” is conveniently forgotten when it obstructs commercial gain.
It's also the case that both advocates and opponents of airport developments will say whatever is required to get their view uppermost. Commonly it is the opponents who spout rubbish, but you get it from the other side too.

[Oscar Charlie 192]

Worth mentioning is that even if you have 2 or 3 runways, if a runway becomes closed due to emergency (let's say an aircraft on fire), there would likely be no landings on the other runway(s) due to insufficient fire and rescue coverage.

Not forgetting the closure(s) to allow the *equipment* free access to the scene.

[FlightDetent]

Thank you! This is what I supposed, but it's great to have it confirmed by people who know what they are talking about. If anyone else would like to add anything it would be appreciated, even if only to support the view above. The plan to re-build and re-open an ages de-commissioned runway 04/22, realigned to increase capacity as 24L/06R

while at the same time

completely close 12/30 and thus remove the noise burden on the west side of the city

sounds like a fair one.

The argument about single runway being not safe does sound silly, however. Apart from the the reasons already mentioned, also because if 24L will not be built the 12/30 is not getting closed!

Anyway, back to your dilemma: If there is a major accident that closes a runway, the attending fire and rescue services cannot provide sufficient cover to sustain operation on the other runway anyway. They will re-group but for a certain period of time 20-40 minutes at least nothing else moves. Some will not be allowed to depart on time, some will need to divert or decide to wait and then divert anyway. The ops will be culled in the immediate wake of an accident but the effect is operationally incovenient, not itself a safety issue.

[rog747]

How dangerous is a single runway, major airport?
Well I guess that was catastrophically demonstrated at Los Rodeos, Tenerife on a Sunday in March 1977.

Sunday was a busy day anyway at TCI (as Tenerife Norte Airport was known then) with many holiday jets coming in all day from all over Europe, Scandinavia, and the UK, often including many big jets 707's CV-990's, DC-8's, VC-10's and the new wide bodies 747, DC-10 and TriStar's.
TCI has a single runway operation 12/30 that had been lengthened to 3,000m, with ILS and a parallel Taxiway. No ground radar.

Throw in the mix on that day a terrorist incident on the nearby island of Gran Canaria meant that the Las Palmas Gando airport there was closed to all inbound traffic (again, Las Palmas is very busy on a Sunday) thus TCI saw many aircraft diversions coming to land there.
LPA ATC would not allow inbound aircraft to hold over the sea, even if they had enough fuel reserves (Of which Pan Am evidently had)

The consequences were was that TCI was soon swamped with very large jets parked up to a maximum on all of the available apron ramps, with the taxiway now also used for parking both the KLM and Pan Am 747 diversions.

KLM's passengers were disembarked into the Terminal but Pan Am's did not.
LPA soon re-opened and clearances were given to start clearing departures, and during this time the notorious foggy weather and low visibility started to close in over the airfield.
Pan Am was ready to go but did not have wing tip clearance to taxy safely past the KLM parked in front.
KLM reboarded, but 4 pax were lost in the terminal.
The KLM Captain then decided to tanker fuel to save time fuelling at LPA thus caused Pan Am more delays whilst KLM now waited for a fuel bowser.
The lost 4 pax (a family) were rounded up and were boarded on the KLM 747.
KLM was finally ready to go...But by now the weather was appalling, fog had quickly closed in, and the Tower could not now see the aircraft.

The controllers plan was for the 2nd 747 (Pan Am) to taxy down the runway behind the KLM and then exit it using one of the transverse taxiways which should clearly/ideally have been at exit C4, a 45 degree left turn, ideal for a 747. This would clear the runway for the KLM plane to take off.
Other aircraft were waiting on C1 and C2 to also join the runway and backtrack, after both 747's had departed.
One of the 747's Crews was completely unfamiliar with TCI airport, it's ATC and that 3 languages were being used.

Most of the rest of that Sunday afternoon is infamously ingrained to History, save to say that would we today allow in almost zero Vis & poor RVR two 747's full of passengers to both taxi down an active single runway together to backtrack the full length ?

[WHBM]

How dangerous is a single runway, major airport?
Well I guess that was catastrophically demonstrated at Los Rodeos, Tenerife on a Sunday in March 1977.

This overlooks that both were departures, so on the segregated scenario discussed would both have been using the same runway anyway.

[Musket90]

rog747 - Another TCI problem was not having appropriate procedures and facilities/equipment in place to operate more than one aircraft at any one time safely in low visibility. The Milan/Linate runway collision in early 2000's involving the SAS MD87 and biz-jet crossing the runway again highlighted this where the biz-jet took a wrong turn, ATC couldn't see the aircraft, inadequate signs, lighting etc.

Regarding close parallel runways used in segregated mode, another capacity constraint is if an arriving aircraft on one runway needs to go around and one is departing on the other runway at the same time then there is an immediate risk of airborne conflict.

[OldLurker]

rog747 - I'm not sure that TCI would count as a 'major airport', except that night, when it was very unusually, and excessively, overcrowded.

The single runway was only one of several 'holes in the cheese' that resulted in the crash; a parallel runway wouldn't even necessarily have prevented an accident under those conditions - under which, as you say, the airport shouldn't even have been operating. Apart from the ones you've mentioned, an important 'hole in the cheese' was the impatience of the KLM captain who attempted takeoff in appalling visibility, such that he couldn't see a 747 backtracking towards him although he knew it was there, without making certain that it was clear of the runway (it wasn't, of course), and despite the attempt of the more experienced, but junior, flight engineer to warn him.

[RHPrague]

Thanks all for the comments. I'm delighted to receive so many.

In case your are interested - maybe some of you know Prague Airport - here is the back-story.

The planned new runway would be to the south of the terminal buildings whereas the current one is to the north, so as I understand it, there would be no need to cross one to reach the other. However the noise issue is that the new runway would bring the trajectory 1.5kms closer to the urban area. The Airport likes to claim that by closing 12/30 it will relieve noise for 200,000 residents but we discovered that in 2019 only 5% of flights used 12/30, whereas 50% of flights would use the new southern 6/24. They have just recently started playing the 'safety' card. One politician last week claimed that it was, in this respect "ordered by Brussels". I'll be on his case!

I am sure it's just a straight business issue, but without any evidence of need. They claimed the capacity would be reached based on growth figures by 2028, but they had no evidence of their own for where this growth was coming from, as I discovered by pressurising them under the Freedom of Info law - the Airport is State owned. I also discovered that Eurocontrol is open and helpful to members of the public who seek help understanding their data. Their forecasts, even pre Covid, didn't support the Airport's growth figures. It looks like a case of "build it, then we'll find some airlines to use it".

I'm a fairly regular flyer (how else would I get back to family and friends in London, especially when i got the call that my Mum had been given 24 hours to live? BA helped get me to her hospital bedside 6 hours after I got the call) and I appreciate Prague needs a good modern airport. But there are other airports in the country which lose money because they are underused, and in regions which need economic investment. And yes, I live in the zone where we would be disturbed by the new flights. But we bought the house in 2002 and as a Londoner of course I tried to do due diligence, with the airport so close, and we were told 'no plans to expand'. Grr.

Basically I supposed that if you guys are happy to fly in an out of Prague, or a similarly configured airport, then the "safety" rationale for a parallel runway is pretty low down the list, and you seem to generally confirm that. For which I, once again, thank you.

[deltahotel]

Single rwy airports in UK off the top of my head. EMA LTN STN BHX EDI. Plenty more in mainland Europe.

[FlightDetent]

It is always awkward when "safety" enters the discussion. Cutting to the chase, most of the time you can recognize a professional and truthful presentation of facts by the author's abstinence from the use of the S-word.

In a traditional case of damned if you do and exactly the same otherwise, any action's benefits have consequences on the negative side and weighing them against each other borderlines with the metaphysical. Sorting facts from chaff according to their relevance for any particular situation becomes impossible on purely technical grounds, without a "just cause" sense of direction.

In this respect, the only universal truth is that absolute safety can only be achieved once we simply stop flying. No airports, no machines, no humans.

As safety is of literal paramount importance what we use in the contemporary discourse (post-1985) is the terms "safety level" or "margin from error". That's the Columbus' egg: A change is to be reviewed relatively to what we already have, or against another possible choice. And this actually gives a good pivot point that even an informed outsider to the industry can use properly.

For your particular case:
1) For a given amount of movements at an airport, does a parallel dual runway configuration provide more room for error margins over
- a) a crossed double runway configuration
- b) a single runway configuration?

It is yes on both accounts. If you listed the genuine benefits of a parallel runway setup, the additional safety factor has a rightful place on it.

At the same time: If someone attempts to use "for better safety" call to justify building a secondary runway on top dubious capacity increase claims, they are destroying their credibility and blowing holes below own waterline.

[RHPrague]

FlightDetent thanks, that's an excellent articulation of the necessary trade-offs, which I shall shamelessly steal.

In the case of Prague, the trade-offs would swing more easily behind "build it", if it were to the north of the existing one, since it would be further away from the city. That raises another point that maybe people can clarify. I have often heard it said that current practice is for new runways, or new airports to be located further away from the urban centres they serve, rather than nearer to them. Is that anything more than just a vague convention? (e.g. has anyone heard of "Brussels" seeking to enshrine it in a directive?). And if so is there a 'safety' element in that convention as well as environmental?.

As far as I know Prague Airport does not consider this because quite simply it does not own land to the north. I found that the northern perimeter fence is also the City boundary. That ought not to matter legislatively for a national asset, but planning law here is not fit for purpose. All kinds of transport infrastructure projects here are delayed interminably because the State cannot easily requisition land.

deltahotel thanks for list of single runway UK airports, very helpful. If anyone can think of similar configurations in North/West/Central Europe for an airport of similar importance, I'd be very grateful. Prague serves a city of 1.3m, has 2 public terminals, and is claiming a current passenger capacity of 21m. I'm not sure about aircraft movement capacities, but I'm only looking for general analogous airports which transport people would see as facing similar challenges.

Again, thanks so much, and I promise to clear off shortly :)

[FlightDetent]

As a citizen and national of the region, I openly declare being insulted by putting PRG and LTN in the same basket.

It is besides the point anyway, because reducing PRG to single runway is not on the cards. As it should not, along with its peers of VIE, BUD, WAW, BER perhaps also OTP, BEG and ATH if you will.
​​

[deltahotel]

Just looking at last night’s destinations comes up with 10+ single rwy airports. Not all huge it is true, but serving big cities GVA BSL SOF. others OPO BLL VNO NTE ORB AOI RIX SKP.

Flight Detent is right - PRG has a long way to go to compete with LTN as a destination!

Also true is (can be) the effect of losing one of the rwys. A few years ago the ac ahead of me on approach declared a Mayday, engine failure, continuing to land. We went around and asked for the other rwy and were told that due fire services involved on the S rwy that the airfield was closed.

[FlightDetent]

Flight Detent is right - PRG has a long way to go to compete with LTN as a destination! Depends if the bike stand in front of Perfect Chicken, East India Dock Road, E14 0ED is part of the destination Luton experience. But that is not appropriate to this thread.

GVA and SOF on your list would count, the others come nowhere close comparable.
2019 data for PRG show
- 10x weekly mainland China (direct to 4 different cities)
- 14x weekly DXB, half T7 half A380
- 7x weekly ICN A380/T7/B747
- 15x daily Russian Federation.

Still a petty regional airport viewed from the seat of the empire but markedly different than the other listed ones. Now comparing Estádio do Dragão with anything in PRG, that's a different sport altogether!

[RHPrague]

I just looked up the passenger numbers for Stansted and Luton. I was staggered to find that in 2019, Stansted, with a single runway, processed 28m passengers.
Prague in the same year managed 17.6m. Luton beat that too, albeit "only" by 1m. From the list of European airports mentioned above, Geneva is already handling slightly more than Prague and there is no talk there of the need for a 2nd runway.
Obviously there are passengers and then there are flight movements, but when I see the Stansted figure, and then the Prague Airport mgmt. bleating that they will hit *capacity* of 21m by 2028, and there won't be any more slots...well I'm just a SLF specimen, but something there doesn't seem quite right. Am I not entitled to say to Prague: "should try harder with the runways you have"?.
I would admittedly prefer to be flying to and from Prague rather than Stansted or the hell-hole that is Luton, but that's about the terminals. And nobody has any problem with Prague investing further in the terminals, which is also part of the plan.

[Bergerie1]

When I was involved in assessing runway capacity and safety back in the 1990s, Gatwick was the most efficient runway in Europe in terms of both safety and capacity at a time when the parallel taxiway was not being used as a second (backup?) runway. And it appears from this link it still is:-
https://www.internationalairportreview.com/article/85317/runway-development-gatwick-capacity/

There are also a number of single runways on remote ocean isands - Bermuda and Seychelles spring to mind. They were operated safely as far as I remember. Single runways are definitely not inherently dangerous.

[FlightDetent]

Happy thread with people keen on facts. :) So shall we endure...

The Prague airport re-construction of 1960-1963 that overlapped the original triangular, British-military-like runway configuration and enlarged its area to the north significantly already planned for a parallel set of 24R/L. Only the northern one (present 24/06) outside the contemporary boundaries had been built, as the construction of the southern one would had shut down the whole airport for about 2 years, intersecting the original triangle in half, and the need for it was not foreseen for some decades then.

The Prague City Master Urban Planning document entered the southern parallel runway - the faulty PR for which is this thread's topic - in 1972. In a sense, the OP is very correct that no new plans for airport development were brewing in 2002, as what had been signed and sealed 30 years before his purchasing time is sufficient even today.

Incidentally, when building new runways in Europe, a quarter of century timeframe is par for the course. Cue the development history of F.J. Strauss Airport (MUC) opening in 1992 having been approved by the Bavarian government in 1969.

[RHPrague]

So in that spirit of seeking facts - or at least opinions of professionals in the field - I have some more questions on the subject.

1.
a) Given that I've just discovered Stansted turns 28m passengers now on a single runway, is it too simplistic to suggest publicly that if Stansted can manage that, then Prague can certainly manage 21m on a main runway plus a reserve? What are the other possible variables when comparing the movement capacity of the two airports?
b) to whom is that question aimed? or rather, who might accidently take it as a criticism? I am wondering if the ATC organisation would be the ones that stipulate how many movements the Airport can schedule in, so they might be the ones who feel they are being unfairly compared with Stansted. Which then leads to the question, which authority regulates how many movements Stansted can safely handle?

2. Different question. Prague's prevailing wind is overwhelmingly westerly, and usually, to someone used to London, benign. So they use 6/24 90% plus times. But they switch to 12/30 when the winds make a rare shift. So what happens if they replace 12/30 with a parallel 6/24?. What if there is a nasty northerly? Do you pilots then just have to cope with the crosswinds? How big a deal is that, in flying terms? (this question applies to all single runway airports I guess)

[deltahotel]

No comment on Q1.

2. If there’s a nasty Northerly then yes, we would! Modern ac have pretty chunky crosswind limits (my 757 is 40kts) and it’s a challenge but trained for. To exceed that would be rare. Be based in Birmingham (BHX) 15/33 and crosswind landings become the norm.

[Musket90]

Q1 - Stansted's 28m passengers (pre-COVID) are based mainly on medium sized aircraft such as B737-800 movements with high load factors and scheduling 50 movements per hour at peak times. Gatwick on the other hand had over 40m passengers (pre-COVID) with a single runway with up o 55 movements per hour at certain peak times. A mixture of wide-bodied and medium size aircraft and also two passenger terminals.

To achieve this runway capacity and passenger throughput there are a number of considerations:
- Have rapid exit turn-offs (RETs) angled and located at the correct distance from the runway landing threshold for the majority of aircraft types likely to use the runway
therefore minimising runway occupancy time.
- Have sufficient taxiways, including runway holding areas to sequence departures and parking stands infrastructure to match the runway capacity otherwise delays will
occur.
- Have a passenger terminal building or more than one terminal to achieve the passenger throughput.
- Have airspace design so ATC delays for departing and arriving aircraft are minimised.
- Another factor with number of movements is environmental and night noise restrictions (normally 2330 to 0600hrs local time in UK) where for example London Heathrow,
Gatwick and Stansted airports have different quotas for each season with Heathrow being the lowest and Gatwick having the highest number.

21m is easily doable on a single runway provided the above issues are considered.

[LessThanSte]

Good thread - an interesting read!

Re 1, i'd suggest there are thousands of variables that would keep airport planners up at night, but some that immediately spring to mind;

ability to get to/from the runway quickly - that would include minimising dead time on the runway before turning off at an intersection and also the ability to get to it quickly/efficiently. For the latter, think of a junction on a major road - if that junction cant cope with the amount of traffic coming at it, it wont be able to efficient shove traffic onto the motorway, even though the motorway might have stacks of capacity remaining. Having rapid exit taxiways, for example, in just the right spots for the major aircraft types will speed things up hugely.
aircraft handling - or in effect everything from getting off the runway to getting back on the runway, including all of the aircraft servicing. I don't know the short/long haul split, and how that compares to, say, Stansted, but any myriad of reasons from employment contracts to facilities to x or y or z could impact the ability to turn aircraft around quickly
number of stands - are there enough, incl. of the right type?
weather - Gatwick operates more or less flat out every day throughout the year with no real weather issues. Does Prague suffer (at all) when its snowy? I'm not saying it falls over completely, but if everything takes a couple of minutes longer that amounts to a substantial reduction in capacity
seasonality - UK airports are fairly busy all year round, particularly in London. Is Prague the same?
Planning restrictions - 21m might be on the basis of noise etc. agreed many years ago. It could be argued (Heathrow do) that having another runway allows that noise impact to be spread out so could be a reason to explore it?
Resilience - i think this is common in the US. FLL for example managed to get a new runway because delays on its existing runway were causing (evidenced) knock on delays across the entire USA, despite only having half the number of passengers of, say, Gatwick. (as an aside, wouldn't it be good if the EU managed airspace/airports across Europe and could use this argument to expand airports this side of the pond, so the 'knock on delays' argument might actually have some legs - maybe Heathrow might happen in a reasonable timescale then!)

There are bound to be more. All of which is to say that it wont be easy to compare two different airports.

As a further thought, talking about passengers may be a bit of a misnomer. Perhaps you could consider ATMs. Do they have dedicated cargo flights, for example? or perhaps they are full to busting in terms of number of aircraft they can land/service a day, but they are all tiddlers (i.e. the passengers per aircraft figure is very low). Having a second runway could allow a diversification of destinations, e.g. allowing more long haul into the mix on bigger aircraft.

To go off on a bit of tangent, a similar debate can be had re active traffic management, e.g. controlling the flow of traffic to maximise capacity/throughput - the principle used on Smart Motorways, for example. This video is useful;

(8) Smart Motorway: Getting smart on the Wellington urban motorway - with Kevin McPhee - YouTube

The reason i raise that is this - if you leave a road as it is, with ever increasing traffic, safety begins to be an issue, normally commencing with nose-to-tail collisions. Increasing capacity, whether through technology to better manage the flow or through building extra infrastructure, allows that traffic to flow better, and safety improves (to a point).

[Musket90]

LessThanSte - Some good points

Regarding weather, it's interesting how it can vary so much at the London airports on a winters day, particularly fog and snow. From my experience Heathrow being west of London tends to get less snow than Gatwick and Stansted with Stansted more likely getting snowfall being over 300ft elevation and it's further east location influenced by north/north east cold winds bringing showers inland from the North Sea.

Gatwick is situated in a valley with a river running nearby so perfect for lower temperature overnight and formation of fog yet at the same time Heathrow and Stansted are clear with higher temperatures. Although Stansted does suffer from fog occasionally in winter in certain weather patterns due to it's rural location and elevation and often Gatwick and Heathrow are clear at the same time.

Another issue with single runway is an alternate in case of diversion. For example if one of Heathrow's runways experienced an unplanned closure the alternate is the other runway but with a single runway airport the alternate would be to another airport, provided of course the ground handling and parking capacity at the alternate is available. I believe with single runway airports aircraft may uplift more fuel at the origin so in the event of a diversion they have sufficient fuel for the alternate airport.

Another issue with the very busy London airports, which includes Luton, if there is an unplanned closure of any of these airports runways then a situation quickly develops where many aircraft are looking to divert at very short notice to other airports and in the space of a few minutes this can cause significant increase in ATC workload. Also some of these airports may not be able to accept these diversions for reasons already mentioned.

Altogether a very interesting and complex subject

[RHPrague]

My perception (which I'd love to examine with data) is that Prague really is a quite benign airport, both re capacity and weather, compared with say Stansted

- when thinking about the runway issue, it suddenly occurred to me that I could not remember the last time I was stacked coming into Prague, whereas coming into LHR it's a red-letter day if I am not. Is that a reasonable indicator of real capacity issues? (and would I be able to request data to underpin it?)
-there is not even that much snow any more (rather sadly) last significant falls were I think 2011 or 2012. I was stuck for three days that year before heading back to London for Xmas, but the problem was snow at LHR not here. Prague has all the gear. No brooms...
- winds as a I said, usually benign. Nary a bump, and i notice these things.
- It is badly located for fog, and it took years after the fall of the communists to get Cat 3 autoland (correct?) . But now that isn't an issue, and indeed the fog itself seems less common, it might have been pollution - fuelled in the past.

I'm very open to getting reality checks on my perceptions - it's why I am here - but so far I come away from this thread even more convinced that at least technically, the parallel runway is a solution searching for a problem.

[deltahotel]

Looking at Musket post, fully agree with paras 1,2,4.

Don’t think using a second rwy at destination as an alternate stacks up. If 27L at LHR is out due weather then so will 27R and at the planning stage the weather requirements for alternate are more stringent than for destination.

That said we are allowed to do it but the weather has to be pretty good (2000’+, vis 5k+) but I can’t remember it in the last 20 years.

rgds

ps. Who doesn’t love Cat3 ops?!

[Musket90]

deltahotel - What I meant by unplanned runway closure was an aircraft emergency/disabled aircraft or perhaps runway surface breakout. It would be extremely unusual for both 27L and R to be out due fog. All LHR runways are CAT III equipped in respect of ILS and lighting, however the IRVR (instrumented runway visual range) for each runway can differ greatly so ATC would likely adjust the landing and departure runway to suit. The downside with fog is runway capacity is reduced due to the need to increase the arrival spacing on approach so ILS signal integrity is not affected. The reduced landing rate figures based on the IRVR value are published in the UK AIP. This results in ATC flow control measures which can result in flight cancellations, mainly short haul, particularly flights where there is more than one daily frequency to/from a particular destination.

[deltahotel]

Sure. Maybe I misunderstood - my point just that even with a two rwy destination we would still carry fuel for a different alternate.

[dixi188]

Had a situation at Heathrow back in the early noughties, when I was waiting for a BA flight to Paris mid afternoon.
A KLM 767 blocked 09R with a wheel bearing failure and a few minutes later a Virgin aircraft taking off from 09L blew a tyre and closed that runway. I don't how many diversions there were but the T4 departure screen suddenly went to all flights cancelled.

[Peter47]

One of the problems is single runway airports without parallel taxiways so aircraft have to taxi down the active runway - LTN & LCY come to mind but there must be many other examples.

Going off topic another major issue the configuration in which runways are operated. La Guardia for example is interesting with take offs and landings on intersecting runways allowing around 70 movements per hour, but this works ok and there are plenty of examples particularly in the US. The most complex I have seen is SFO which combines two sets of intersecting close parallel runways - two almost simultaneous take offs in one direction followed by two not simultaneous but closely spaced landing (presumably a heavy must follow a lighter aircraft rather than the reverse). This allows up to 90 movements per hour including a number of heavies which works ok in good visibility but I have seen delays due to "bad weather" in conditions that wouldn't raise an eyebrow at airports like Heathrow.

Taxiing aircraft having to cross active runways is always an issue (ATL, LAX, etc). ATL is interesting in that it is the only example I can think of of a "grade separated" taxiway. (If you haven't seen it aircraft taxi past the end of the runway and an aircraft that is landing off or landing could be directly overhead.)

[treadigraph]

One of the problems is single runway airports without parallel taxiways so aircraft have to taxi down the active runway - LTN & LCY come to mind but there must be many other examples.

Before parental bankruptcy forced my employer's closure three years ago, my civil and structural engineering colleagues were working on a further major upgrade to facilities at London City, including decking over the dock to carry a full length taxiway. This work was successfully handed on to another consultancy to complete (think my some of my colleagues transferred too) and looking at Google maps, the decking is being constructed so presumably it won't be too long before the taxiway is in use.

[Musket90]

Peter47 - In Luton's case whilst the parallel taxiway doesn't extend to the runway ends most departures which are not performance limited can accept the reduced distance when departing from an intersection so avoiding a backtrack of the runway to the full length. I believe in USA airports like SFO use the automated "runway status lights" system (red lights) which hopefully mitigates runway conflict issues. There's a video on YouTube about Paris CDG runways status lights which may be the only European airport to provide them.

[DaveReidUK]

Taxiing aircraft having to cross active runways is always an issue (ATL, LAX, etc). ATL is interesting in that it is the only example I can think of of a "grade separated" taxiway. (If you haven't seen it aircraft taxi past the end of the runway and an aircraft that is landing off or landing could be directly overhead.)

I suspect you are referring to "End-Around (https://www.caasd.org/library/documents/end-around_taxiways.pdf)" taxiways (grade-separated means one passing over/under the other). ATL is one of a dozen or so US airports with EATs, and there are a number in Europe including AMS, BCN, FRA and MXP.