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Last month we published a video arguing the case for circular runways at airports, as part of a series called World Hacks. It took off and went viral.

The video has had more than 36 million views on Facebook and generated heated debate on social media - including within the aviation community. Many people are sceptical about the concept.

So we decided to hand-pick some of the top concerns and put them straight to the man proposing the idea: Dutch engineer Henk Hesselink.

This is what he had to say.