A drone was flown deliberately within 20 feet of a light aircraft, its pilot has claimed.
It happened as the PA-31 twin-engined plane was coming in to land at RAF Northolt in west London on 11 June.
The pilot "lost sight of" the drone under his plane's nose, a report from the UK Airprox Board (UKAB) said.
It was "identified as a small white drone of the lightweight hobbyist type", the report added, and it passed about 20 feet below the aircraft.
The small, remote-controlled device "passed close to his right wing and was possibly launched from a park".
The pilot had "no doubt that it was being deliberately flown under the flight path in an attempt to collide with an aircraft".
An airprox is a situation in which two aircraft get close enough to compromise safety.
There were six near misses between drones and aircraft in 2014 – rising to 93 last year.
Research has found that a drone weighing 2kg could critically damage an airliner's windscreen, while a lighter one weighing 400 grams could smash a helicopter windscreen.
The incident in Northolt posed the most serious degree of risk, UKAB said.
Police could get the power to issue on-the-spot fines of up to £300 for the misuse of drones, as well as the power to seize them, under proposals being considered by the Department for Transport.
It is also considering banning children from owning drones weighing at least 250 grams.
Drones are already banned from flying above 400 feet, and within 0.6 miles (1km) of airport boundaries.
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Anyone breaching those rules faces fines of up to £2,500.
They could also be charged with recklessly or negligently acting in a manner likely to endanger an aircraft or any person in an aircraft, carrying a maximum sentence of five years in prison.