Three Airbus A380 flights were involved in drone encounters within London terminal airspace over the space of two months last year, according to UK investigators.
The UK Airprox Board's latest run-down of incidents involving unmanned aerial vehicles shows that a drone flew within 20m of a Heathrow-bound A380 operating at 3,400ft over central London on 22 July.
It states that the aircraft was carrying out an ILS approach to runway 27R when a "large commercial drone" passed down the right side of the aircraft. Police contacted the aircraft's captain to record the event.
Twelve days later, on 4 August, another A380 crew, descending for Heathrow, saw a drone pass the aircraft on its right side at 4,200ft after it had captured the localiser for a 27L approach. The Airprox Board gives the separation as 60m horizontally.
Both incidents have been classified in the highest collision risk category.
The board has disclosed a third A380 incident on 29 September in the vicinity of Holmer Green, which lies 27km north-west of Heathrow.
It says the event involved an aircraft climbing through 7,300ft. The crew stated that a "medium-sized drone" was seen around 50m ahead, and that it "passed overhead", estimating the vertical separation at 200ft.
While this incident was categorised as bearing a slightly lower risk, another high-risk encounter had occurred four days earlier with a Boeing 787 at 9,000ft.
"The captain [of the 787] raised his head from looking at the instrument panel and saw a small silver aircraft pass very rapidly from level with the flightdeck to below the left wing," says the board, putting the separation at 150ft vertically.
"It was a very brief sighting of the craft as it flashed past at high speed. It was silver metallic and appeared to be descending in the opposite direction."