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Comment by pdonis | Hacker News Reader

> If they need more capacity they’ll build parallel runways which will be named with a suffix, like 9L and 9R.

There are even some airports that have three runways with the same heading, so they have "L", "C", and "R". (Two examples that I've personally took off or landed on all three of are 17/35 at DFW and 01/19 at IAD.)

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Or 4 parallel runways like Detroit Metro (KDTW): 4R, 4L, 3R, and 3L.

https://aeronav.faa.gov/d-tpp/2213/00119AD.PDF

KDEN also has four parallels (16-34L/R and 17-35L/R). All are 172.6º or 352.6º.

KDEN also put their runways so close together that it's not uncommon to for aircraft on approach on the parallel to set off another airplane's TCAS. I think most airline pilots consider that airport ripe for a midair.

Atlanta has five parallel runways: 27R, 27L, 9R, 9L, and 28/10. It appears the main four that are close to each other are set alternating east landing and west landing as they're not marked on both ends like 28/10 is.

They are numbered on both ends on both the satellite view (real-world) and on the FAA diagram: http://aeronav.faa.gov/d-tpp/2213/00026AD.PDF

There would be no (or extremely rare, at a minimum) operational reason to alternate directions for takeoff and landings on parallel runways. (There are rules for simultaneous operations to parallel runways and having them be in opposite directions would be problematic as you have to assume some aircraft will execute a missed approach and would then be climbing into opposite direction landing traffic with only a small lateral offset.)

About the closest I can think of to that is some mountain airports that do all takeoffs one way and all landings the other. I’m not aware of any of those with more than one runway and traffic is usually extremely limited.

27L and 9R are the same runway, always. 27R and 9L are the same runway. In Atlanta, besides 27L/9R and 27R/9L, there's also 26L/8R and 26R/8L, as well as the 28/10 you mention. See https://aeronav.faa.gov/d-tpp/2213/00026AD.PDF

This is the same dodge that ORD uses, as DocTomoe pointed out: pretending some of the runways are a different heading when they're actually not. I'm not sure how that can be avoided with four runways, though, since I don't see how to fit a fourth option in with "L", "C", and "R".

In fact, taking this dodge into account, the DFW example I gave actually has five parallel runways; the two they label 18/36 are actually the same heading as the three they label 17/35. I wonder if they'll ever need to go to six and add an 18/36C.

What's L C R and why can't there be more letters?

Left, Center, and Right.

There is also the following suffixes for runway identification: S = STOL runway, G = glider runway, W = water sealane or waterway, and U = ultralight runway. For example runway 8G / 26G in KBDU (Boulder) and 3W / 21W in KSFF (Spokane).

Could just go A B C D E left to right I guess. If only 3 use B C D so the middle is always C regardless of system.

You want to have a consistent designation for opposite direction runways. (9R is always the same piece of pavement as 27L)

Doing that for 4 would need one direction to be A B C D and the other to be B C D E (which is workable, but doesn't seem particularly more elegant than just using left, right, and center [and in fact is worse in some ways, since from one direction, B is the left-most and from the other, it's A])

Also, EDDF/FRA, in which one runway got renamed to C when they opened a smaller one in the 2010s.

Then you have airports like ORD which have more than three parallel runways - but pretend some of them are ten degrees off to get more naming space. [1]

[1] https://upload.wikimedia.org/wikipedia/commons/a/aa/FAA_O%27...

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