UK investigators have disclosed that an Airbus A321 was checked for damage at London Heathrow after a drone encounter so close that the crew initially believed it had struck the jet.
The A321 had been conducting its approach to runway 27L on 27 October last year, according to the UK Airprox Board.
It states that the crew witnessed a three- or four-engined white drone pass over the first officer's windscreen at a distance of just 5ft.
"The crew considered that the drone passed close enough that it must have collided with the tail," says the board in a newly-released summary of airprox incidents following a meeting last month.
Weather conditions at the time were excellent, with little cloud and good visibility.
"No tangible evidence of collision could be found after landing," says the board. "The aircraft was released back into service."
It has classified the incident as one bearing the highest risk of collision. The board has not identified the operator of the A321.
Investigators have also detailed two other high-risk drone airprox incidents, both at Manchester airport, which occurred in November – one involving an Airbus A320 and the other involving a Dornier 328.