A study of London's future airport needs said four runways in one location was needed but Heathrow Airport is not a viable option.
Expanding Heathrow has become a bone of contention in London, as proposals for a new runway have run into opposition due to the lack of available space and the added airline noise.
Johnson commissioned a study on the matter, which was conducted by York Aviation. The study said four runways are needed at one location "rather than spread haphazardly across the south-east."
"The need for a single, large hub airport is undeniable -- without the transfer passengers it collects, it is not viable to lay on many of the direct routes to destinations that are so beneficial to our residents and businesses here in the U.K.," said Daniel Moylan, who advises Johnson on aviation issues.
"This new data further illuminates the need for that airport to have at least four runways and room to grow, because it is spare airport capacity that allows airlines to innovate and experiment with new routes to emerging markets. This is a description of a national asset that Heathrow, with its severe size constraints and dire noise impacts, can never become," Moylan said.