1931: Airport on top of King’s Cross Station, London
This article is from Retronaut. Click the title to hop over there.
“It was envisaged that planes would approach down a new ‘Aerial Way’ above the Pentonville Road, landing on one of the half-mile concrete runways. In the 1930s, London had no skyscrapers, so the approach would have been obstacle free.
Businessmen who owned their own small planes would be able to store them in garages under the runways, which would be brought up by lifts when they were going to be flown.
There were two problems with the concept, though: firstly, the design meant the runways could not be lengthened at a later date, and secondly, if a plane careered off one of the numerous edges, it would be a catastrophe.
The “Aerial King’s Cross” features in Felix Barker and Ralph Hyde’s excellent 1982 work London As It Might Have Been, a collection of architect’s plans for London which were proposed but never built. Additional information from Airports: A Cemtury of Architecture by Hugh Pearman (2004.)”