"We are studying the possibility of changing the current rules and imposing a minimum space between the seats for all constructors who want to be registered in Europe," said Elisabeth Schöffmann, a spokeswoman for the European Aviation Safety Agency (EASA).

EASA, which is based in the German city of Cologne, believes the change is necessary to decrease the risk of injury in the event of an evacuation of the aircraft, Schöffmann said.

Health risks

Authorities also fear there is a growing risk of deep vein thrombosis (DVT), which is the formation of a blood clot in a deep vein, most commonly in the legs.

The condition has been dubbed the "economy-class syndrome" because passengers sitting on long-haul flights without space to stretch out are considered the most vulnerable.

The average space between seats in economy class is currently about 80 centimeters (31 inches), although the smallest space is about 69 centimeters. EASA gave no indication of how much larger it wanted the new space to be.

EASA is currently in talks with aircraft manufacturers and national aviation authorities about the issue.

European Union legislation stipulates that planes must be able to be evacuated in under 90 seconds, but imposes no criteria on space between seats.