Last November, a passenger plane encountered two drones as it approached London's Heathrow Airport. The UK Airprox Board (UKAB), the organisation that investigates airborne near-collisions, has issued a a report stating that the incident "compromised the safety of the aircraft".
On the November 20 last year, as an Airbus A320 was 5,500 feet over East London and heading towards Heathrow Airport, members of the crew spotted two drones, which the report estimated were as close as 500m to the plane. Pilots kept "constant visual contact" with the drones.
Less than thirty minutes later, another aircraft approaching the airport - a much larger Boeing 777 - flew within 50 meters of what appeared to be one of the drones from the earlier incident. Both incidents were reported to the Metropolitan Police, who were unable to locate the people who flew the drones.
The British Civil Aviation Authority (CAA) has ruled that drones may not be flown 400ft above or near UK aircrafts and airfields. Despite this, the PA news agency reported 3,456 incidents in the UK involving aircraft and drones last year, including an incident that occured 500ft above a primary school. This is a big increase from the 1,237 incidents that were reported by the agency in 2015.
The CAA has further stated that the November 20 incident was the first near-miss with an aircraft that involved more than one drone.