Do most airports (especially busy ones) use only one runway at a time for landing? For example, I know Heathrow uses only one of its runways at a time (although they might switch to another half way through the day).
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2$\begingroup$ Half way through what? $\endgroup$– Caius JardCommented May 26, 2020 at 19:46
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$\begingroup$ Does this answer your question? What determines in which direction a runway is used? $\endgroup$– PondlifeCommented May 27, 2020 at 15:38
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$\begingroup$ Many "busy" international airports (LAX, CDG, AMS,...) have more than 2 parallels runways. Even if using form landing only and another one for take off only, it would still allow the use of another runway. You should restrict your question to international airports with exactly 2 runways. $\endgroup$– Manu HCommented May 27, 2020 at 17:22
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2$\begingroup$ Statistically speaking, most airports only have one runway $\endgroup$– 60levelchangeCommented May 27, 2020 at 17:51
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$\begingroup$ I just remember some international airport use parallel landings. SFO is a famous example. $\endgroup$– Manu HCommented May 27, 2020 at 21:36
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2 Answers
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In general, any runway can be used for both takeoffs and landings. However, switching back and forth requires substantial safety margins. If you can use one runway for just takeoffs and another for just landings, efficiency goes up. If those runways are parallel, efficiency goes up again. This is why major airline hubs tend to have pairs of parallel runways.
Averaged over a day, the number of takeoffs and landings should be about the same, so the normal mode would be to split the runways as evenly as you can. If the number of runways isn't even, the last runway will often alternate throughout the day to mitigate short surges in one or the other.
As to which runways are used for what, the ones used for landing should be as far from each other as possible to maximize lateral separation of arriving traffic on instrument approaches. (Departing traffic mostly separates itself.) So, if you had four runways organized as two pairs, you'd expect the "inner" one of each pair to be used for takeoffs and the "outer" one of each pair for landings.
In the case of Heathrow specifically, runway usage is largely dictated by noise abatement agreements with nearby towns, rather than what makes the most sense operationally.
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$\begingroup$ Depends on the airport and the traffic. For instance, at Reno (RNO) airlines and other large planes generally use 16R/34L, smaller planes use the parallel (and shorter) 16L/34R. However, it's not at all unusual for smaller planes to use 7/25 if there's no conflicting traffic. (Especially since crosswinds can sometimes be pretty strong on 16/34.) $\endgroup$– jamesqfCommented May 27, 2020 at 4:08
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$\begingroup$ I don't agree that "substantial safety margins" are required for runways with mixed departure and arrivals. Departing and arriving flights use roughly the same amount of time on the runway - typically around 45-60 seconds. You can do landing-takeoff-landing-takoff with 1 minutes between each flight just as well as you could do several takeoffs or landings each with one minute between $\endgroup$ Commented May 27, 2020 at 17:56
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$\begingroup$ @J. Hougaard: Though you need appropriate spacing/separation for wake turbulence. $\endgroup$– jamesqfCommented May 28, 2020 at 5:28
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$\begingroup$ @jamesqf There a mix of arrivals and departures is actually an advantage, since you will automatically have twice the spacing between consecutive departures and consecutive arrivals $\endgroup$ Commented May 28, 2020 at 14:19
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Airports will usually divide their active runways about evenly between takeoffs and landings. KATL (Atlanta Hartsfield Jackson) has 5 runways, and currently operates 2 for takeoff and 2 for landing. Most airports that can operate more than 2 runways simultaneously will use them all, unless the traffic is just very low.
Heathrow is exceptional in that it is one of the busiest airports in the world, and only has 2 runways.
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$\begingroup$ Do you know where I can find information on how runways are assigned at each airport? For example, Beijing has 3 runways. I want to know whether two of them can be used simultaneously for landing. $\endgroup$ Commented May 26, 2020 at 20:14
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$\begingroup$ How far apart are they? That is key - they need to be far enough that wing vortex from one landing aircraft doesn't impact the adjacent runway. I looked that up for the USA, if I recall 4300 feet was needed. $\endgroup$ Commented May 27, 2020 at 0:15
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1$\begingroup$ Heathrow has 2 strips and 4 runways as each strip has a runway in each direction. $\endgroup$– GdDCommented May 27, 2020 at 8:18
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1$\begingroup$ @GdD It's completely normal to refer to a strip as one runway although it can be used from either end. I don't think anyone is in doubt about what zymhan means by two runways. Claiming Heathrow has four runways would be misleading in most situations. $\endgroup$ Commented May 27, 2020 at 18:00
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1$\begingroup$ @Teodorism you can follow live ATC or flightradar24 during few hours to see actual assignation. $\endgroup$– Manu HCommented May 27, 2020 at 21:38