Why Circular Runways may never be reality?

Courtesy: BBC News

The concept of circular runways aka ‘The endless runway' is a concept that dates back to experiments in the 1960s and is currently being pursued and researched by the National Aerospace Laboratory in the Netherlands. The biggest advantage of circular runways is that an aircraft can land and take off from any direction thus eliminating the dreaded crosswinds, but does the concept work other than in theory? I'm afraid it may have more challenges than advantages.

Some of the advantages are:

1) The capacity of an airport with an Endless Runway is at least similar to that of a conventional airport with four runways, while the length of the circular runway is comparable to three. This helps in having traffic active on the same circular runway.

2) Dangerous crosswinds are avoided as a different arrival point in the circular runway can be chosen such that there are headwinds.

3) The terminal is constructed in the center of the airport hence saving on the amount of land that is cleared.

What are the challenges?

The biggest challenge is for pilots to be able to take off and land an aircraft from a banked runway. Starting from the inner part of the circle on a flat surface, the bank angle will gradually increase to the outside. Because of the centrifugal forces, a starting aircraft at the middle of the circle will move to the outer part until taking off. There is less scope for error since the aircraft wings can easily hit the runway due to the sloped nature of the runway, hence making it more difficult for pilots and less safe. The pilot also has to constantly steer the aircraft after touch down in order to maintain the curved path and during high speeds the steering is dangerous. If nose wheel steering fails the aircraft will crash and there is nothing the pilots can do since using asymmetrical thrust to steer takes more time and is unstable. A rejected takeoff may cause a collision with traffic landing or taking off because a rejected takeoff is unpredictable and the braking distance is dependent on a lot of factors.

How will ILS work on a circular runway?

ILS (Instrument Landing System) is a precisional approach that almost all runways are equipped with that help pilots to line up and descend onto the runway. ILS is the several antennas at the end of the runway that uses radio waves to communicate with the aircraft’s autopilot. Circular runways will need multiple ILS antennas and the pilots can use ILS only to a certain point in the approach hence making even ILS a non-precisional approach. It would be impossible for an aircraft to perform an auto-land on a circular runway, hence making them a nightmare in low visibility conditions.

Challenges faced during icy and rainy conditions:

When it’s raining the water constantly runs off the sloped runway making the aircraft more prone to skidding off the runway during takeoff roll or landing. Under icy conditions, a circular runway is an invitation for disaster since it’s difficult for an aircraft to remain stable on a conventional runway when there is ice build-up. Researchers have proposed a solution to heat up the runway to remove ice but it’s not feasible to heat up such large areas.

Cost and feasibility:

The estimated cost of building a circular runway is almost 1.5 times the cost of building a conventional airport. The cost is, even more, considering the training of pilots and air traffic controllers. Aviation today has been built on decades of convention and regulations, a circular runway will make most of them obsolete and overall a hard experience for the flight crew to adapt to it. The circular runway has a minimum diameter of 3.5 kilometers in order for the passengers to feel lesser g-force, this large area can be used only for major cities that handle a lot of traffic. If a circular runway is built what can be done with the old conventional airport? A city cannot obviously have both. It does not seem feasible to clear out such large areas in major cities to build circular runway airports, at the same time having to demolish the old conventional airport, after it’s completed. Considering the challenges the pilots face along with the safety concerns, conventional airports emerge triumphantly.

In conclusion, a circular runway is definitely a revolutionary concept and in theory is very successful but when applied to the reality and exposed to different scenarios it is definitely not feasible or safe.

Thanks for reading!

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