An unusual smell caused a Lufthansa flight carrying 91 passengers to London City airport to return to Frankfurt shortly after take-off on Monday.
The plane, an Embraer 190 flying for Lufthansa's CityLine subsidiary, was checked by the airport fire services, but the cause remained undetermined.
"We take this very seriously," a Lufthansa spokesman said. The passengers were transferred to other flights.
A week ago, a Lufthansa flight landed in Geneva after a suspicious smell in the cockpit raised the alarm.
