A technical problem paralysed Frankfurt airport, for almost an hour on Thursday, forcing the cancellation of around 60 flights and the diversion of more than 20.
The hitch meant the German Weather Service was unable to transmit visibility data for pilots and air traffic controllers between 6:35 am and 7:25 am.
The air traffic controllers had no reliable visibility data at a time when there was a light early morning fog, said flight security spokesman Dirk Pulver, reported dpa.
"As a result, the air traffic controllers were required to operate under "conditions of adverse visibility" and extend the time gaps between planes starting and landing, he said.
This led to the cancellation of 60 outgoing flights and the diversion of between 20-25 incoming flights to other airports, Pulver said.
Frankfurt airport, Europe's third busiest after London and Paris, was used by more than 60 million passengers last year. dpa ms bve