The Metropolitan Police have opened an investigation into reports that a drone struck a commercial passenger plane as it approached London’s Heathrow airport.

On Sunday, the pilot of a British Airways flight from Geneva, Switzerland, reported that a drone had struck the front of the Airbus A320, which was carrying 132 passengers and five crew members. British Airways inspected the plane but found it was undamaged and deemed safe for its next flight.

No one has been arrested following the incident and it is not known who owned the drone or why it was being flown in an area with so many passenger planes. In the U.K., airports and their surrounding areas are controlled airspace where the flying of drones is prohibited.

Steve Landells, from the British Airline Pilots Association (Balpa), told the BBC it had been “only a matter of time before we had a drone strike.” The Civil Aviation Authority, the U.K.’s airspace regulator, reportedly said it was “totally unacceptable” to have drones being flown close to airports.

The investigation into the incident, which is believed to be the first of its kind, will be led by the Metropolitan Police’s aviation security unit that is based in Heathrow.

While there have been no reported incidents of drones striking passenger planes, there have been numerous reports of close calls. Last July, two passenger planes narrowly avoided colliding with a drone as they approached JFK Airport in New York, according to the Federal Aviation Administration. The FAA says such incidents are far from rare, with the regulator getting up to two reports every day from pilots saying they have spotted unmanned aerial vehicles.

A report in December by New York's Bard College’s Center for the Study of the Drone reviewed 921 incidents involving planes and unmanned aerial vehicles between December 2013 and September 2015. It said that 327 of those incidents involved drones getting to within 500 feet of an aircraft. “Our findings indicate that incidents largely occur in areas where manned air traffic density is high and where drone use is prohibited,” the report said.