A drone was flown within a few metres of a passenger jet landing at Heathrow Airport, continuing a recent spate of near-misses.
The pilot of the Airbus A319 stated that the drone may have been just 20 feet (six metres) above and 25 yards (23 metres) to the left when it passed by the aircraft.
He told the UK Airprox Board (UKAB) that it was not possible to take avoiding action and the incident was put in the most serious risk category.
The jet was flying at an altitude of 500 feet and was on the final approach to the west London airport on September 30 when the drone was spotted.
Officials said that the drone was flown against Civil Aviation Authority regulations because it did not have permission to be above 400 feet within the Heathrow CTR control zone.
It was concluded that separation between the drone and the jet had been reduced to about a wingspan - described as "the bare minimum" - and that "chance had played a major part" in the avoidance of a collision.
Although a report was made to the police, the drone operator was not traced.
The UKAB noted that the drone had not shown up on radars.
Steve Landells, flight safety specialist at the British Airline Pilots Association, has previously called for designers to look at ways to make drones visible to air traffic controllers.
The latest monthly meeting on near-misses analysed a total of six possible incidents between aircraft and drones.
On October 2 the pilot of a Dornier Do328 short-haul jet - which typically has capacity for around 30 passengers - reported a drone passing his left wing by less than 50 feet (15 metres).
He believed it must have passed over the propeller and assessed there was a high risk of collision.
The incident occurred at an altitude of 3,000 feet shortly after take off from Manchester Airport.
There has been a surge in reports of drone near-misses in recent months, with the UKAB published details of seven events after its December meeting.
They included a drone coming within metres of colliding with a jet above the British Houses of Parliament on September 13.