A major air catastrophe over central London was averted "by pure luck" after a drone almost hit a passenger plane.
The Airbus A320, with up to 165 passengers aboard, was making a final approach to Heathrow over the famous Shard building when the "near-miss" occurred.
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The aircraft was just 200m (650ft) east of the 310m (1,016ft) high skyscraper, which is the tallest building in western Europe.
The pilot spotted the black drone through the cockpit window.
The crew watched as the object, about 50cm (20in) across, hovered over the right wing and then over the right horizontal stabiliser next to the tail fin.
A report said only good luck prevented a collision. The plane was descending through 1,500m (4,900ft) at 180knots – about 200mph – close to the 95-storey building.
It was the third drone near-miss in consecutive days involving airliners coming in to land at Heatrow.
A day earlier, an Airbus A319 pilot saw a large drone pass 100m away down the left hand side of his aircraft.
The day before that, an A320 pilot saw a drone fly within 15m of his wing tip as he was coming in to land.
Investigators at the UK Airprox Board, which examines near misses in British airspace, said July's Shard case was "a very near miss".
The report said: "The Board considered that the pilot's estimate of separation, allied to his overall account of the incident, portrayed a situation where a collision had only been narrowly avoided and chance had played a major part."
The Board branded unmanned aerial vehicles a "genuine risk to flight safety".
They said people who fly them too close to planes should face jail.
The Civil Aviation Authority says a drone should never be flown higher than 122m (400ft).
Pilots warn a drone could destroy an airliner's engine or smash a cockpit windscreen. And the lithium battery could catch fire on impact.
The operators of the drones in all three incidents could not be traced.