Here's an aviation mystery to sit alongside the Bermuda Triangle and the disappearance of Amelia Earhart.

A British Airways Airbus A380 set off from Hong Kong on May 5 with 22 round wheels -- but apparently touched down at London Heathrow with a bizarre square-shaped tire.

This extraordinary photo was uncovered by aviation news site The Aviation Herald , which reported that the British Airways crew received a tire pressure warning shortly after takeoff.

The crew continued with the flight but requested that a tow tug be available at the London airport in case the aircraft was unable to taxi to the gate by itself.

'Not seen anything like it before'

l e v a r t

Thirteen hours later, the plane landed safely on runway 09L and was able to taxi to the gate without assistance.

But then, reports The Aviation Herald, it was discovered that the right outboard tire had deflated both top and bottom, creating a curious four-cornered shape.

It's been puzzling aviation experts.

A Civil Aviation Authority spokesperson told the Daily Mail : "It's a curious one. Not seen anything like it before."

Patrick Smith, author of Cockpit Confidential, confessed: "The photo appears genuine, but I'm unsure how such a thing would happen, exactly."

How did it happen?

Kumar Mysore, from the Royal Aeronautical Society, told the Mail that the square shape might be due to how the weight of the Airbus A380 distributes itself on a deflated tire.

"You can see that the wheel is not damaged at all, as it is designed to take this weight.

"The effect is the same as when you squeeze a rubber ring toy with different intensity, it can turn into a different shape.

"In an A380, for this particular situation, it happens to be squarish."

Mysore assured the Daily Mail that while there were a number of possible reasons for the deflation, "pilots are well trained to handle the situation safely."

A spokesperson for British Airways also confirmed that the flight was not in danger.

"Our flight landed normally last Friday with one of its 22 tires deflated.

"The A380, in common with other large commercial aircraft, is designed to be perfectly safe when landing with a deflated tire.