# Why do airports remove/realign runways?

When looking at Google Earth, I often find myself looking for airports. I often notice that no matter what size airport, over time many of them have abandoned old runways and built new runways in different directions.

It doesn't matter between rural and urban, so residential doesn't seem to be the cause. Is it that the wind direction changed from decades ago? Did they decide that sunlight matters more or less at some point in time? Anything to do with Earth's magnetic field?

In some cases the prevailing winds change and certain runways fall out of use. Since airports tend to be land limited they may wish to use the land for hangars or other facilities so the runways are eventually decommissioned.

In other cases it could a noise abatement issue, many airports predate the property development that often surrounds them. It may be in the best interest of the local neighborhood to change the runway orientation to one that creates less noise and pollution over homes or businesses.

In some cases runways may be moved to comply with changing regulations as was the case at Aniak Airport, where an existing runway no longer complied with obstacle clearance regulations.

In some cases it also becomes expensive to maintain a runway that may not see much use and it will be shut down.

Magnetic shift generally wont cause a runway move but it may cause a runway re-number since the runways are numbered as per their magnetic heading.

• thank you for your reply. I did look up Aniak and found a youtube video of the local Alaska legislatures shaking their heads at having to spend an estimated $53M to move the runway. – doug Jul 5, 2019 at 0:44 • @doug literally shaking their heads? Feb 21, 2020 at 16:06 Three runways (or pairs) 60 degrees apart was very common. Where land was limited, two runways (or two pairs) at 90 degrees was almost as good. These generic designs could be built very quickly almost anywhere and work well regardless of the prevailing winds, which was particularly important when building hundreds of them in a hurry during WWII. However, the needs are different. Modern jets need longer runways than WWII planes but aren't as sensitive to crosswinds. And there is now decades of data on which runways were used the most at each airport, so only those were extended. At the same time, traffic has grown, and building new runways parallel to the main one(s) adds capacity faster than it adds costs, so it makes sense. Some airports kept the intersecting runway(s), but it(they) don't provide anywhere near the capacity now, still cost a lot to maintain and take up valuable land that could be reused for fancy new terminals or hangars, so many airports have ripped some or all of them out. • Thank you for your reply. Your answer has helped my understanding, especially regarding the idea of how quickly so many runways must have been built across the country. – doug Jul 5, 2019 at 0:56 • One example where you can see that change from 60-degree-separated runways to longer parallel runways is Heathrow. Even in current aerial photos, the location of the old runways is still clearly visible. The two 09/27 runways were extended, the other runways were turned into taxiways, ramps, and built over with terminals and other buildings. Jul 5, 2019 at 6:10 • +1 for mentioning adding parallel runways. This seems to be the primary reason for large commercial airports. As the required capacity keeps growing, several commercial airports have gone away from having crosswind runways at all in favor just having as many parallel runways as they can, which is by far the most efficient if it's feasible. ATL comes to mind. ORD is another example where old runways in different directions were closed or turned into taxiways to make room for more parallel runways. Jul 5, 2019 at 6:52 • Just to note, the part about runways being built in WW2 would be specific to mainly European countries, no? Feb 21, 2020 at 16:08 • @Michael You can see it across the US (training bases) and Pacific islands (operational bases), not just Europe, and I'd assume anywhere the air war reached. The same designs appear postwar in other countries too, just not as many of them. Feb 22, 2020 at 0:01 In the US, one of the most common reasons to abandon one or more runways is that a large military airbase built for intensive World War 2-era training has passed into civilian hands-- county, municipal, or private ownership-- and it is too expensive to maintain all the runways, especially considering the vast reduction in traffic. For example, if you visit the airnav page for SN76 and look at the aerial photo, you'll see the short stretch of fresh blacktop on the one maintained runway, with remnants of a vast system of other runways and taxiways still clearly visible. This former military airfield is now privately owned. This explanation wouldn't apply to small airports though-- there would at least be some visible evidence that a larger airport had once been there! • Thank you for your comment. I do often find myself looking for small civilian airports and find myself wondering about their history, and why the change. For instance, I found the Canyonlands airport outside Moab, Utah. Nothing that I could see that would necessitate a change, yet there it was clear as day. I completely understand your comment regarding WW2 runways as we have several abandoned airstrips in north Florida. – doug Jul 5, 2019 at 0:52 • @doug Yeah, the area around Eglin AFB has tons of those abandoned and/or repurposed runways. It's pretty interesting to look around there on aerial imagery. Old runways turned into parking lots for rusted-out tanks and such. Jul 5, 2019 at 7:03 Some airports have had to rebuild runways as the size and weight of planes using them has increased. Occasionally, the underground geology under the old runway may not be suitable to support the newer heavier planes. For example, a runway built near the water may be on soft or marshy ground. This ground may need to be reinforced to handle heavier planes. Also, it is generally not desirable to take a runway out of service completely while rebuilding it so you will build a new runway nearby and then decommission the old when one when the new one is complete. Multiple reasons. 1) Changes in prevailing local winds can necessitate new runways though this is probably the least desirable reason to do this as runways cost between \$1-\\$3 million per mile, depending on type, layout capacity, etc.

2) Airport expansion and upgrades to accommodate larger heavier traffic. Sometimes this is possible to simply upgrade or lengthen an existing runway. Often times preliminary civil engineering studies conclude this is not practical and a site for a brand new runway is chosen. One prime example of this was Van Nuys airport (KVNY).

It is not about a change in winds, but more about having any weather data at all. Recording weather was very primitive even 60 years ago. and many locations cicra world war 2 did not have any recorded wind data beyond a local farmer holding up a finger giving a generalized guess. so they did the 60 or 90degree thing. Many WW2 airports had a triangle of three runways, one will get very little air-side use and may be used mainly for taxi.

Another change is in the instrument approach procedures. These, like weather information, were also very primitive in the 1940s and it may be difficult to make a modern procedure to certain runways due to terrain obstacles or competing airspace issues. In these cases a runway may have less value than its cost to maintain. Also you don't want a VFR plane using a crossing runway in marginal visibility while an IFR flight is on final approach when the tower is closed.

• It's not just (lack of) weather data, particularly for repurposed WWII-era military airports. It's that the planes were mainly fairly high-performance taildraggers, which didn't handle crosswinds all that well. So even if 90% of the time winds favor one runway, if the other 10% you have a strong crosswind on it, you still want to be able to take off and land. Oct 14, 2020 at 4:55
• "IFR flight on final approach when the tower is closed"? IANAP, but can you fly IFR into an untowered airport with declaring an emergency? Oct 14, 2020 at 17:13
• @FreeMan Yes, IFR to untowered airports is normal everyday procedure. Both for private and air-carrier operations. Oct 21, 2020 at 4:33
• #TIL. As I said, not a pilot... Oct 21, 2020 at 10:54