flying

"From an engineering perspective it's so much easier to build a drone that can fly than to build something that can keep them from flying," Jensen, from the University of South Denmark, points out.

Inside there’s a sense of calm, order and welcome — flying in the face of what is, in many cases, a sterile, institutional environment.

It inspired fierce loyalty among its pilots, yet also acquired the grim nickname "flying coffin" after a series of deadly crashes in its twilight years.

"We cannot yet comment on the purpose of the drones flying in the area, nor can we say anything about who the actor behind it is," chief inspector Jesper Bøjgaard Madsen said.

Between two to three large drones were seen flying in the area around Copenhagen Airport, according to authorities.