Incoming flights were suspended at Gatwick Airport for nearly an hour after reports of a drone near the airfield.
It said 12 incoming flights had to be diverted to other airports because of the alert on Sunday.
The airport previously cancelled or diverted around 1,000 flights between December 19-21 2018 because of drone reports.
No culprit was found, and there was criticism over the amount of time it took for the runway at the West Sussex airport to reopen.
A Gatwick spokesman was unable to say whether a drone had been discovered after the latest reported sighting.
The spokesman said: “Passenger safety is the airport’s absolute priority and – following established procedures – operations at London Gatwick were suspended temporarily at 1344, while investigations into the sighting of a suspected drone close to the airfield took place.
“These investigations have now completed and the airfield reopened at 1435. Twelve inbound aircraft were diverted to other airports during the investigation, however we expect many of these to return to London Gatwick today.”
British Airways said one of its flights was affected, with it landing at Stansted before refuelling and returning to Gatwick.