BERLIN (AP) — Flights to and from Frankfurt Airport were interrupted briefly Friday after a drone was seen in the area.

Operator Fraport said takeoffs and landings at Germany’s busiest airport were suspended as a precaution for 29 minutes late Friday afternoon, news agency dpa reported. They resumed after federal police using a helicopter found no more sign of the drone.

Airport officials initially said two drones were sighted but revised that information.

Around 60 of Friday’s 1,439 scheduled Frankfurt flights were canceled, but that was largely because of an unrelated computer problem at an air traffic control center. The drone caused some extra delays, Fraport said.

The popularity of drones makes them a growing threat to aviation.

More than 100,000 travelers were stranded or delayed right before Christmas last year after drone sightings near London’s Gatwick, Britain’s second-busiest airport. No one has been arrested over the incident, which saw the airport shut for parts of three days.