Tuesday morning saw a scare for passengers on a Qantas flight as oxygen masks dropped suddenly.

Qantas flight QF670 was 30 minutes from Melbourne, its destination after departing from Adelaide, when the aircraft’s cabin suddenly depressurised and triggered the mask deployment from the overhead consoles. The pilots immediately commenced a rapid decent and the plane landed safely in Melbourne shortly thereafter. None of the 99 passengers onboard were hurt in the ordeal.

Reports said that immediately after cabin pressure was lost, the pilots made an announcement that the Boeing 737-400 would be making a rapid descent to 26,000 feet. Once that altitude was reached, they contacted air traffic control and received clearance to descend to 10,000 feet, an altitude with safe levels of oxygen, and cruise there for the remainder of the way to Melbourne.

Qantas spokeswoman Sophia Connelly confirmed with reporters that cabin pressure had been lost in the aircraft and that the masks had dropped. She added that they were not deployed by the pilots but were triggered automatically by the aircraft’s monitoring system. She said that officials suspected the problem was caused by the jet’s air conditioning unit, but that had yet to be confirmed.

Peter Cowan, a passenger on the flight and a frequent flyer, said to radio 3AW that the event was ‘fairly scary’, as on all the flights he’d ever experienced it was the first time he saw depressurisation and mask deployment.