A Delhi-bound Singapore Airlines (SIA) Airbus A-380 with nearly 300 passengers on board had to return to the island nation soon after take off on Thursday after its overhead oxygen masks got deployed.

The flight 406, which the airline websites says is operated on the super jumbo A-380, landed safely in Singapore and passengers are going to be sent to their destination on another aircraft.

“We are sorry for the disruption to your flight this (Thursday) evening. After (getting) airborne the onboard oxygen masks were deployed without command. After taking safety into due consideration, a decision was taken to return back to Singapore. We will deploy another aircraft to deploy this service. Also, as the crew has exceeded their legal operating hours, we will operate with a new set of crew,” SIA said in a note to its passengers.

The deployment of oxygen masks is supposed to happen when cabin air pressure falls due to any reason. In such situations, the masks provide oxygen for such time that the aircraft descends to a level where plane can take in air from outside. The aircraft has to land at the nearest airport thereafter.

However, sometimes the oxygen masks get deployed without the cabin pressure falling. But even in such cases, aircraft have to land at the nearest airport. “There was no depressurisation on SQ 406 and the deployment of happened due to a systems error,” said an SIA spokesperson.