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March 20, 2017

Why The Circular Runway Concept Would Not Work

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Written by: Phil Derner Jr.
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I honestly thought it was a joke at first. It raised so many questions and concerns in my mind that I thought it was a satirical piece in The Onion. But alas…

This video has been going viral, even among those that do not follow the aviation industry. To learn that the Netherlands Aerospace Centre has been researching this for years with government funding, I must concede that they may have answers and solutions to my below issues that were not provided in the short BBC report. Though I can see why this idea may sound appealing, I feel that the moment that conditions are not absolutely ideal in that best-case bubble, the concept collapses, opening up the probability of delays, and the possibility of an increase in accidents.

It is worth noting, however, that circular runways are not a new concept. Today, any airport can be referred to with the technical term of “aerodrome,” but in the early days of aviation it specifically referenced airports that had large round runways. Not a turning, perimeter runway, but instead comprised of a giant circle that allowed aircraft to land straight and flat, in any direction across the middle of the circular field. This, of course, would occupy an absurd amount of space at modern commercial airports.

Banked Runway Issues

This designer says the aircraft can land at a slower speed, which I don’t see as necessarily safe. Wings will generate the most efficient lift when level to the ground, perpendicular to the demands of gravity. Any rolling or banking affects that, increasing the stall speed of the aircraft, making it more dangerous to fly slower.

This is concerning when planning for the event of engine loss during takeoff, which is a part of pre-flight calculations before every single departure. An aircraft already working hard to climb in this scenario would now be faced with getting away from the runway at a bank angle that is not generating its most efficient lift. Though you could conceivably let it land right back down on that same runway, sudden thrust differential on a banked and curving runway adds two variables to stopping the ailing aircraft. This is not to mention that you may have other aircraft on other sections of this perpetual runway that this aircraft would now be encroaching on. That means that what would otherwise be a well-practiced and non-issue engine loss instead receives more possible contributing factors to an accident.

Another big concern to me is traction. For every single flight, a large variety of factors is calculated to determine braking distance, and one of the more important ones is “contamination,” referencing precipitation or moisture that is on the runway. A runway that is wet, even without standing water, increases stopping distance, as does patchy snow, compacted snow, ice and all of the different variables we consider. The centrifugal force they advertise would lose effect as the aircraft slows, further killing traction.

Now imagine something remotely slippery, on a slanted runway. An aircraft trying to stop on a sideways slide that must also slowly turn down pavement that’s curving as well. How many runway excursions would be caused by aircraft sliding off of the edge during winter operations?

Curved Runway Issues

Aside from the curve affecting stopping on a contaminated runway, I have a concern about the curve making it difficult for the aircraft to even touch down on the centerline. While almost every landing is safe, not all landings are perfect. It is not uncommon for flights to get down to the runway and float some feet above the surface for a little, captured in what is called “ground effect.” On a curved runway, while the pilot is trying to comfortably plant the wheels down (while in a bank above the slanted runway, mind you), the centerline of the curved runway will be drifting off-center to its side, now adding the need to also turn the aircraft to the pilot’s workload. This level of challenge is the airline equivalent of landing on an aircraft carrier.

Navigation Issues

A claimed big selling point of the circular runway theory is that, because an aircraft can land anywhere in the circle, they can always land into the wind, ending the need to battle crosswind landings.

“Anywhere in the circle” becomes a challenge when considering how the aircraft will navigate to that specific, ever-changing touchdown zone. Unless visibility and cloud cover is wonderful, having precision guidance systems and visual aid lighting in place is vital to a safe (and delay-free) operation. With this new runway, how would that equipment be moved and adjusted, possibly flight by flight or hour by hour as winds change, to that moving landing zone?

Airspace Issues

When it comes to airspace, the two biggest “selling points” of the circular runway are being able to operate into the wind and also allowing 3 aircraft to land at once, brings about tremendous contradiction.

First, if wind is anything less than calm or very light, there is no way that 3 aircraft can land simultaneously in different areas of the circular runway if you are trying to avoid crosswind. If attempted, though one may be lined up nicely into the wind, the other 2 would then be landing with crosswind, with 1 of those experiencing both a crosswind and a tailwind (tailwinds are usually not permitted when over 10 knots). This makes this giant stretch of round pavement a single runway operation in any singnificant wind. So, congratulations, your extra special runway just took on an arrival rate worse than Newark.

Second, and more importantly to me in terms of safety, what about go-arounds? What if 3 airliners are landing, something goes wrong and they abort landings. Their prescribed go around procedure would likely take them dangerously close to the other aircraft also trying to land or go around themselves in more congested airspace than conventional runways with a parallel approach. And yes, multiple go arounds at once can and do happen, as Murphy demands.

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Too good to be true

Keep in mind that one of the main motivations behind this is for it to be a solution to “tricky” crosswind landings. This is confusing to me, because aside from my feeling the idea doesn’t even do that effectively because of new threats it brings to the table, crosswind landings are not the safety threat that sensationalized headlines would make you believe. Though wind can and does cause delays at certain airports, crosswind landings have not caused an epidemic of accidents, or even small amount of fatalities in recent times by any measure.

Crosswind landings look scary for sure, but they are example of skilled airmanship that you should be in awe of, not frightful of. Clearly defined crosswind limitations and the ability to easily execute a go around if an approach becomes unstable are why air travel is as incredibly safe as it is. Those videos are examples of aviation safety working effectively. Websites that post videos of “wild,” “scary,” and “frightening” crosswind landings are clickbait. The creator of the circular runway concept even admits that he was “inspired by watching scary crosswind landings on YouTube,” not from any challenge or need that the aviation industry is actually facing. Pilot unions are not making demands for a solution to crosswind landings, and I feel this idea fails the sniff test from those with a working knowledge of aircraft, airline and airport operations.

In aviation, we have built the amazing safety culture and safety record that we have by figuring out everything that can go wrong, finding a solution to it, and then figuring out what we would do when that solution goes wrong, too. This “circular runway” concept only adds more, unnecessary variables that can go wrong, while not even solving an existing problem to begin with. Though I give it the thumbs down personally, I applaud organizations and people that are thinking. Even if this concept is were to not end up as a winner, it can lead to other ideas that will take us into the future.

Phil Derner founded NYCAviation in 2003. A lifetime aviation enthusiast that grew up across the water from La Guardia Airport, Phil has aviation experience as a Loadmaster, Operations Controller and Flight Dispatcher. He owns and operates NYCAviation and performs duties as an aviation expert through writing, consulting, public speaking and media appearances. You can reach him by email or follow him on Twitter.



About the Author

Phil Derner Jr.
Phil Derner founded NYCAviation in 2003. A lifetime aviation enthusiast that grew up across the water from La Guardia Airport, Phil has aviation experience as a Loadmaster, Operations Controller and Flight Dispatcher. He owns and operates NYCAviation and performs duties as an aviation expert through writing, consulting, public speaking and media appearances. You can reach him by email or follow him on Twitter.




 
 

 

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  • formertcresident

    I just don’t understand how you could do any sort of precision approach using this type of runway. This to me is one of the most major hurdles. During multiple approach ILS type conditions, this would be useless.

    • Dan Krámek

      Perhaps they will expect another funding of circular propagation of electromagnetic waves… 😀

  • Alex

    Perhaps for automated, computer controlled, landings this would be an effective system but that is not for a near future (I hope! as I still trust a seasoned pilot better on a crosswind than a computer), I can also imagine moving ILS emitters, that would slide along a rail according to the approaching aircraft’s direction. This makes for interesting, thought provoking, science fiction, but I agree with all these remarks and that this concept raises more problems than it solves (if it solves any at all).

    But someone (Soarfly Concepts) is designing a scenery using this concept for use in flight simulators so soon any pilot or virtual pilot will be able to test this concept! Where else, after all?

  • I don’t understand how someone could write “I must concede that they may have answers and solutions to my below issues that were not provided in the short BBC report.” spend all this time writing this post and not look at the originating site, and read some of the hundreds of pages of research and documentation behind it. It may well be nuts but it deserves better than a drive-by shooting. http://www.endlessrunway-project.eu/documents/index.php

    • Lloyd, you’re right, that is very fair. I admitted that my write up was first impression for that reason exactly. Maybe I will do a follow up.

      • Thank you for your response, this is only the second time in 15 years of writing that I have criticized another writer, and I got a very different response the first time. But this is a really interesting incident; I am an architect running a big design site and this popped up on another design site. Not knowing anything about the subject I started searching and found that you are not alone; at least three other experienced and authoritative sources did exactly the same thing, going on for pages about how this was crazy without going past the video.

        But when I looked up that source, I ended up spending the afternoon reading document after document about it, and his answers to every one of these concerns. I don’t understand a lot of it and it is probably still totally wacko, and I cannot comment on anything but the land use and urban planning issues and implications, where I am quite impressed.

        I have done this myself, reacting instantly to some architectural concept, some energy saving idea that where I just start hammering out negativity. It is so much easier in a field that you know.

        And again, thank you for your response.

  • John Oddvar Hauge

    I think i have been in to all of that thougts, but i find it very interesting. Perhaps was´nt it so great when the first rondabout came either? Of course you need an testfeeld, but this idea realy saves space even if the radius is 2 km.

  • Kurt Ruhwald

    Very good points, but don’t forget that the bank angle required to make the turn on landing or take-off would be about 45 degrees which is an abnormal manoeuver for an airliner. The “Bank Angle” aural warning would be going constantly.
    Also, every aircraft has a different take-off distance and landing distance depending on type, weight, and air temperature; therefore ATC would never know exactly which direction a departing aircraft would going in and whether that would potentially conflict with an arriving aircraft. In fact the whole idea shows a lack of understanding of traffic separation. This concept would result in only one aircraft being able to approach and land or take-off and depart at a time, resulting in an incredible lack of efficiency and capacity at a major airport.
    It is also doubtful that any hoped for space saving could be achieved as the arrival and departure obstacle clearance requirements around such a runway would take up vast amounts of space on which no structure, light post, or tree would be permitted.
    There is nothing about this idea as currently envisaged that is safe.
    I am an airline pilot with 30 years of airline experience.

    • Espen Johansen

      How on earth did you come up with 45 degree banking? Secondly a circle of 3.5 km and 100 meters wide would easily provide you with more then 0.5km of straight runway with absolutely no need to turn your rudder at all. I dont think I would like to fly with you as a captain if your understanding of aviation basics are this low. I hope you aren’t serious. You are right about 1 thing. A airport like this isn’t feasible everywhere. But in places like the Netherlands, which is really flat, this is feasible almost everywhere. As for the paths for takeoff and landing with up to 8 paths (N,S,E,W, SE, SW, NE, NW). This will make sure that in any kind of wind direction there will allways be atleast 1 takeoff and landing path that can be used simultaneously. Takeoff and landing will then be 180degrees separated and 3.5km LOS apart. And have a runway seperation of 5.5km. Those mentioning crossing paths for takeoff and landing seems to have completely missed the point.There will be a maximum of 3 takeoff and landing paths. The landing path will have quite a low angle in. While the takeoff paths will be much steeper. So the conflicts of crossing paths are just BS. The most efficient way to take in planes with low winds are to do a multiplexing pattern of takeoff and landing with maybe 5-10 mins window for either takeoff or landings. Or to mux them landings/takeoffs/landings/takeoffs. And as I worte before, a multi frequency ILS/MLS/PAR in up to 8 directions would take care of this.
      And finally, the runway banking would be less then 5 degrees so this is not an issue.

      • Kurt Ruhwald

        You asked: How on earth did you come up with 45 degree banking?

        Simple mathematics; first we need the radius of the runway: we find the radius using the circumference and the circumference of a circle is 2 r.
        I used miles, so 3.5 miles of circular runway is 18,480 feet so plugging that
        into the equation we find that the radius is 2,941 feet or just under a half nautical mile (0.48 nautical mile). We need to convert to nautical miles because speed is measured in knots, you’ll why this is important. Then to find the bank angle we use the equation D=(TAS)2/(34208 x tan B) where D is the diameter, and B is the angle of bank. Rather than take up space here for arithmetic, we can use an App in a smart phone like FlyBy E6B.
        Plugging in the speed at which the mainwheels on my fully loaded jet
        liftoff the runway 174 knots and .48 nm radius we find that a 43 degree bank is required for a 0.47 nautical mile radius turn. (close enough, or don’t you
        agree?)

        You said: Secondly a circle of 3.5 km and 100 meters wide would easily provide you with more then 0.5km of straight runway with absolutely no need to turn your rudder at all.

        I don’t know what kind of aircraft you are thinking would use a circular runway, but I thought we were talking about jet airliners. Mine needs a lot of runway.

        You said: I dont think I would like to fly with you as a captain if your understanding of aviation basics are this low. I hope you aren’t serious.

        Yes, I am serious and I think you should be more careful about whom you disrespect in a public forum. I am near the end of my career and therefore no longer have anything to prove to anyone, so I don’t care what you think of me. Most professionals would likely leave you to wallow in your ignorance but I don’t mind explaining things to you because it would probably benefit more people reading this than just yourself.

        You said: Takeoff and landing will then be 180degrees separated and 3.5km LOS apart. And have a runway seperation of 5.5km.

        Airliners NEED to take-off and land with not more than 10 knots of tailwind so therefore landings and takeoffs would take place in roughly the same direction, certainly not 180 degrees apart except in very light wind.

        You said: Those mentioning crossing paths for takeoff and landing seems to have completely missed the point.

        I think that what you are not understanding is that take-off distance and landing distance varies with aircraft weight, air temperature and wind speed. Looking at take-offs; Since every aircraft is not identical and even the same type of aircraft vary in their weight depending on their load (fuel, passengers and freight) it should be obvious that every aircraft would depart in a different
        direction from a circular runway. It would be chaos.

        You said: There will be a maximum of 3 takeoff and landing paths. The landing path will have quite a low angle in. While the takeoff paths will be much steeper. So the conflicts of crossing paths are just BS.

        No, not BS; the wake turbulence of departing aircraft overflying the path of a
        landing aircraft would have serious destabilizing effects on the landing
        aircraft. Also, in the event of an engine failure for the departing aircraft
        the flight paths for the departing aircraft and the landing aircraft could
        intersect. I know that would be a rare occurrence, but why take the chance?
        Modern aviation got its safety record by not taking chances.

        You said: And finally, the runway banking would be less then 5 degrees so this is not an issue.

        As I explained above: at normal take-off and landing speeds banking of close to 45 degrees is required and results in 1.4 G’s.
        Not having the runway banked would exceed the landing gear side load
        limits causing disaster.

    • Espen Johansen

      Kurt, your reply is gone so Ill put it back here:
      You asked: How on earth did you come up with 45 degree banking?
      Simple mathematics; first we need the radius of the runway: we find the radius using the circumference and the circumference of a circle is 2 r.
      I used miles, so 3.5 miles of circular runway is 18,480 feet so plugging that
      into the equation we find that the radius is 2,941 feet or just under a half nautical mile (0.48 nautical mile). We need to convert to nautical miles because speed is measured in knots, you’ll why this is important. Then to find the bank angle we use the equation D=(TAS)2/( 34208 x tan B) where D is the diameter, and B is the angle of bank. Rather than take up space here for arithmetic, we can use an App in a smart phone like FlyBy E6B.
      Plugging in the speed at which the mainwheels on my fully loaded jet
      liftoff the runway 174 knots and .48 nm radius we find that a 43 degree bank is required for a 0.47 nautical mile radius turn. (close enough, or don’t you
      agree?)
      You said: Secondly a circle of 3.5 km and 100 meters wide would easily provide you with more then 0.5km of straight runway with absolutely no need to turn your rudder at all.
      I don’t know what kind of aircraft you are thinking would use a circular runway, but I thought we were talking about jet airliners. Mine needs a lot of runway.
      You said: I dont think I would like to fly with you as a captain if your understanding of aviation basics are this low. I hope you aren’t serious.
      Yes, I am serious and I think you should be more careful about whom you disrespect in a public forum. I am near the end of my career and therefore no longer have anything to prove to anyone, so I don’t care what you think of me. Most professionals would likely leave you to wallow in your ignorance but I don’t mind explaining things to you because it would probably benefit more people reading this than just yourself.
      You said: Takeoff and landing will then be 180degrees separated and 3.5km LOS apart. And have a runway seperation of 5.5km.
      Airliners NEED to take-off and land with not more than 10 knots of tailwind so therefore landings and takeoffs would take place in roughly the same direction, certainly not 180 degrees apart except in very light wind.
      You said: Those mentioning crossing paths for takeoff and landing seems to have completely missed the point.
      I think that what you are not understanding is that take-off distance and landing distance varies with aircraft weight, air temperature and wind speed. Looking at take-offs; Since every aircraft is not identical and even the same type of aircraft vary in their weight depending on their load (fuel, passengers and freight) it should be obvious that every aircraft would depart in a different
      direction from a circular runway. It would be chaos.
      You said: There will be a maximum of 3 takeoff and landing paths. The landing path will have quite a low angle in. While the takeoff paths will be much steeper. So the conflicts of crossing paths are just BS.
      No, not BS; the wake turbulence of departing aircraft overflying the path of a
      landing aircraft would have serious destabilizing effects on the landing
      aircraft. Also, in the event of an engine failure for the departing aircraft
      the flight paths for the departing aircraft and the landing aircraft could
      intersect. I know that would be a rare occurrence, but why take the chance?
      Mode rn aviation got its safety record by not taking chances.
      You said: And finally, the runway banking would be less then 5 degrees so this is not an issue.
      As I explained above: at normal take-off and landing speeds banking of close to 45 degrees is required and results in 1.4 G’s.
      Not having the runway banked would exceed the landing gear side load
      limits causing disaster.

      Now please do your calculations again. Diameter is 3.5km Circumference is 10.9 KM or 5.88 nautical miles. Meaning r is 1.75km, a nautical mile is 1.852 so r is 0.94 miles. I stand by my comments earlier. My education is systems avionics, I know what I’m talking about.

      • Kurt Ruhwald

        OK, Epsen, my mistake the diameter is 1.75 nm. That still requires 25 degrees of bank and takes it from the ridiculous to the merely dangerous. A banked runway is still required as the side loading would still be significant. This larger diameter still doesn’t mean it is safe and does not address any of the MANY other problems affecting this idea.

        • Espen Johansen

          No, it less then 5 deg. In a circle with 3.5km ID and width of 100m (ca 330ft) you can make a hexagon on top of it. That will give you 6 straight lines. Now do the math again. From any direction you can land with less then 5 deg banking and you will have a straight touchdown path of more then 1500 ft before you would need to turn rudder/nose wheel. Is this really that hard to understand?

        • Espen Johansen

          Please get your numbers right. Metric to nm isnt that hard.
          1nm = 1.852 Km = 1850 meters.
          Now the Circumference is 10.99km (36056 feet) this gives you a half circle runway of 18028 feet. Or 1/3 circle of 12018 feet runway without overlap. Without knowing what kind of equipment you are running I dont know the exact tolerances. But even a A380 could land without problems on this kind of runway.

          • Kurt Ruhwald

            Yes, I know how long a nautical mile is. I can’t debate this with you any longer. If you refuse to accept my word that there are too many dangers associated with this idea then you will just have to wait and see that none will ever get built, maybe you will believe me then.

          • Espen Johansen

            We will see once they start running this in the 737-800 simulator. And you have yet to show any debate. You just stated a bunch of math with wrong numbers and subjective opinions. The r is not 1.75nm either but 1.88nm. If you want anything more then stating your subjective view, then I’m here to answer as best I can.
            If you draw a scale circle with 3.5inches ID and a circle with 3.7 inches OD. Then you draw a vitual hexagon on top of it. This will show you the virtual straight paths. The straight path will be used for initial touchdown and braking. Then you will start to follow the curved line as you slow down even further. The virtual hexagon will show you how much of a straight line you will have for initial touchdown. For takeoff you will accelerate to around 100-120mph with a 737-800 while turning, then you enter a straight line while accelerating to 160-180mph and take off. If you redo your calculations based on correct numbers, then we can have a proper debate rather then your so far subjective “I say so”.

  • torqueback

    Yes, the idea has been around for decades… but the skies are more crowded now. When are you going to stack incoming aircraft if they can approach from any direction? If they’re being stacked, won’t they then all be coming in from the same direction? Or will you have to invent moving stacks? It’d be chaos – wouldn’t it?

    • Espen Johansen

      Expansion would be a larger diameter. Banked landings are no problem. 8 ILS/MLS /PAR paths would fix the flight paths automation. Circling while waiting for landing permission is normal. 1 path can allways be used in strong winds. Octagons can be used too, but would require a larger diameter. This is totally feasible. It will require some new and out of the box thinking and ideas, but none of the challenges mentioned by those opposed to the idea are even close to beeing showstoppers.

      • torqueback

        What you say makes sense… but I live in the U.K. We can’t even build a third runway at LHR because we have no space. A great concept for mid-continental locations with thousands of square miles of adaptable land but, with space at a real premium and when population density is as high as it is here (and it’s that population that use aircraft), I can’t see many circular runways being built, never mind expanded. And there’d be too many adjacent airports to make approach/ air traffic control practical…

  • Robert B
  • clearhd

    ..a round continuous banked runway will have its realworld technical problems.. but an oval runway will have both of the advantages: leveled flat runway along the stretch & a round banked runway at both ends making them likewise continuous and never ending.. the leveled flat runway along the stretch is where the planes can land or takeoff like an ordinary runway but could continue its path once it reaches the end of the runway for whatever reason.. this is a tweak from the original design and study and is worth the consideration.. another tweak is squared.. where the corners are banked and the sides are flat & leveled.. making them likewise continuous.. but i prefer the oval approach.. the banking can be done that enough inclination will make the bend as if it was traveling on a straight path.. if you have taken a test track like the one in Nürburgring (or the Ring..) Germany… you will realize that the banking makes you feel that the tracks are just straight, very little steering wheel turn adjustments are needed..