, , , , ,

Don’t be fooled — 10 Reasons Why Circular Runways Are a Bad Idea

A BBC News video on circular runways has been making the rounds lately on social media.  The video has almost 30 million views! The concept of a circular runway is pretty unique.  In order to save space and reduce delays, an airport should consider other designs.  An EU-funded researcher proposes that airports should ditch the concept of runways and instead build one long circular track where multiple aircraft could land simultaneously on different parts of the track. Pilots love innovation, especially in an industry like aviation where the necessity for near absolute safety can sometimes trump progress.

To the uninitiated, the idea makes sense.  The ‘revolutionary’ design supposedly increases traffic flow, distributes noise more fairly, and isn’t that uncomfortable for passengers.  Sounds great, right?

Not really. This idea is as dumb as a football bat. What’s even more disappointing is that the BBC reporter barely knows enough about aviation to challenge this ‘expert’.  A ’news’ story like this one should be downright embarrassing for a major worldwide-news network. Here are 10 reasons why the concept of circular runways are not only impractical, but downright stupid:

1.) Banked Runways mean Higher approach speeds

A banked runway means that an aircraft would have to fly its final approach with a slight bank.  An aircraft’s stall speed increases with any bank.  Therefore every airliner approaching this new type of field would have to fly faster.  This increases landing distances and thus wear and tear on brakes and tires.

2.) That headwind turns into a crosswind and maybe even a tailwind.

A circular runway’s big sell is that you’ll land with a headwind.  However, that also means that the wind’s vector will change on arrival or departure roll (takeoff). That’s not a big deal on a calm spring day but imagine the challenge during a gusty summertime storm. It’s much easier to keep a jet going straight than to try to keep a jet at an exact bank angle (that isn’t straight and level) during gusty winds. Now try making corrections on a landing while trying to make a gentle right turn too. It’s dangerous.

3.) Poor visibility and winds will equal disaster

Gusty winds and poor visibility would make this ‘innovative’ idea a disaster waiting to happen. As a pilot, I’ve only flown CAT II approaches to minimums. At 100 feet, you have just a split second to determine if the lights you see through fog is a McDonalds sign or the approach lights on a runway. If it is a runway, you have about 3-5 seconds to sure you line up correctly to a very straight runway. I couldn’t imagine the difficulty of adding a curved runway in that situation. Add in a CAT III style approach (near zero visibility and ceiling) and it would be damn near impossible.  It would be like driving a NASCAR around a track at 150 mph in zero visibility!

4.) Where do you put runway equipment and how do you mark this new runway?

With the limited exception of some types of GPS approaches, all precision approaches require ground sensors and stations to provide vertical and lateral guidance. This equipment is expensive and sensitive. It’s expensive enough that you couldn’t put an infinite amount of localizer sensors on a field to create the infinite runways that the innovator describes. Even if you could do it or standardize the signals to place one in one every quadrant, you’d still have planes from other departure quadrants interrupting the line of sight position feedback to arriving jets. That’s a big no-no in aviation where safety is paramount.

Even worse, airports would require completely new runway markings and naming convention for a circular runway. This isn’t a small challenge. You not only have to come up with a new system, you then have to train every pilot on something as basic as runway markings.

5.) Your captain would become a student pilot again

Changes that force pilots to learn new skills in aviation are pretty common. What is unprecedented though is a change that is so fundamental as how to land a plane. This would require massive, massive retraining in procedures, intense expenditures for flight training, and new types of instrumentation inside and outside the cockpit. This change is equivalent to forcing a heart surgeon to use chopsticks and a butter knife to do a heart transplant. Circular runways would challenge every known procedure and (at least temporarily) take aviation experience and safety back to the 1930s.

6.) Land and Hold Short Procedures are Inherently More Risky Than Full Length Runways

One circular runway would require multiple airplanes to be on the same runway at the same time. With the exception of military aircraft, the closest civilian procedure that we have today is called LAHSO. This means that aircraft are arriving and departing on intersecting runways. While LAHSO procedures are fairly common, each LAHSO means that a pilot accepts and increased risk that an aircraft will land and continue beyond a hold short point.

7.) Engine scrapes will be much more common

Most airliners these days have wing mounted engines. On a 737, a bank angle of greater than 15 degrees could result in a nacelle strike. That is on a flat runway. A banked, circular runway means that the outward facing wing will have even less margin before a strike during a sudden wind shift. Strikes can damage engines. A severe strike could sheer off the engine and threaten controlled flight.

8.) Ice and rain make landings more difficult…Turning on an icy runway? Not going to turn out well.

Have you ever driven on a slippery or icy highway? Planes are basically big tri-cycles on the ground. At takeoff, planes can speed up to 170mph. It’s much safer to go those speeds while moving in a straight line. Large airliners have been known to slip onto the grass at taxi speeds while turning during poor weather. A gradual turn on a degraded runway surface at approach or takeoff speeds could be very dangerous.

Delta 1086 (Photo by Leonard J. DeFrancisci)

9.) A rejected takeoff would now be even more dangerous

If an aircraft loses an engine on takeoff, the pilot makes a split second decision to continue the takeoff or stop and apply max braking. Max braking means that the pilot uses his/her toes to apply maximum pressure to stop the jet going straight ahead. With a circular runway, max braking would either be prohibitive due to the need to directionally steer (using differential braking and rudder pedals) or the crew would have to accept that they would stop straight ahead and they are likely to depart the runway. Either way, it’s bad news for the plane and its passengers.  If you add in a loss of hydraulic pressure (required for most large aircraft steering systems), you’ll definitely go off the edge of a circular runway.

10.) Sheared landing gear

Turning at high speeds creates shearing forces on the landing gear. Damage is more likely to happen when landing (on a flat runway) in crosswind conditions. The loading forces when landing on a banked runway in a crosswind are much higher.  Gear aren’t nearly as strong in a side-load.

Bottom line?  If circular runways become a reality then I’m taking a bus or a boat.

Written by Jeff Gilmore

Jeff Gilmore

Jeff is a former active duty Air Force pilot who founded Avgeekery.com and now works in Silicon Valley. A longtime #avgeek, Jeff loves technology, aviation, model airplanes, and his family.