The Airbus A320 on a flight from Hobart to Melbourne had commenced descent from flight level (FL) 350 to FL210 when the aircraft cabin altitude began to rise rapidly. The co-pilot was unable to control the cabin pressurisation manually.
The flight crew donned oxygen masks, and the pilot in command requested and was given a clearance by air traffic control for an immediate descent to 10,000 ft. During the descent, the passenger oxygen masks deployed. The aircraft subsequently made an uneventful approach and landing at Melbourne Airport.
The operator found that the electronic control of the pressurisation outflow control-valve had failed, allowing the valve to remain in the fully open position. The valve was changed and the aircraft returned to service. The valve has been returned to the manufacturer in France for further evaluation.