A passenger jet landing at London's Heathrow airport had an extremely dangerous near-miss with a drone, investigators say.

According to a new report out this week, a 180-passenger Airbus A320 was beginning its descent toward a Heathrow runway this summer when a pilot noticed a "helicopter-style" drone flying nearby. The drone was not visible on air-traffic controller screens and police were unable to determine who was flying it.

Experts say the effect of hitting even a small drone could be devastating, pointing to the 2009 Hudson River emergency landing, caused by a plane hitting a flock of geese, as an example of the risk.

Britain's Civil Aviation Authority gave the incident an A-rating, meaning investigators assessed a "serious risk of collision," the BBC reports.

The secretary of the British Airline Pilots' Association, Jim McAuslan, says it's only a matter of time before something serious happens.

"Unless we put in place the regulation now and have enforcement procedures that are practical in operating efficiently then we are going to see an accident," he told Sky News.

[image via Shutterstock]