All flights departing Heathrow, the U.K.’s largest airport, were suspended for an hour on Tuesday following a reported drone sighting.
An airport spokesperson told TechCrunch that staff are “working closely” with London’s Metropolitan Police, “to prevent any threat to operational safety.”
The airport did not say who reported the drone. Shortly after departing flights were halted, flights resumed. “We have resumed departures out of Heathrow following a short suspension,” a spokesperson said. “We continue to monitor this situation and apologize to any passengers that were affected by this disruption.”
The Metropolitan Police tweeted that it “received reports of a sighting of a drone” near Heathrow after 5:00pm local time, where commercial drones are programmed to not be allowed to fly, and that it was investigating.
Arriving flights continued to land at the airport during the disruption. Flight tracking site Flightradar24 showed dozens of planes circling around Heathrow during the ground stop.
Heathrow is one of the busiest airports in the world, with some 80 million passengers traveling through its terminals last year.
It’s the second reported drone sighting at a U.K. airport in as many months. Gatwick Airport south of London faced two days of disruption following a reported drone sighting just before Christmas. In the end, more than 1,000 flights were cancelled, leaving tens of thousands of passengers stranded. No arrests were made following the Gatwick incident (a local couple was released without charge on December 23).
U.K. police were given new powers to fight drones, including an expansion of exclusion zones around airports.
Gatwick said that it had spent £5 million ($6.3 million) on new technology to combat drone sightings, according to the BBC. Heathrow also said it would invest in new anti-drone technology.
A spokesperson for the Civil Aviation Authority, which regulates U.K. airspace, did not immediately respond to a request for comment.