Air/pressurisation involving a Boeing 737-377, VH-CZP, 20 km south-east of Townsville, Queensland, on 6 November 1993

During the climb, at about 5,000ft, the crew became aware that the aircraft cabin was not pressurising. Alternate selections were tried without success. The captain then decided to proceed to the destination at FL130 after briefing the cabin crew to be alert for any passenger distress and to administer oxygen from portable bottles if necessary. In accordance with safety requirements, the captain and first officer both donned oxygen masks for the flight above 10,000ft.

After reaching cruise level, several passengers and one member of the cabin crew reported headaches and light headedness. The captain descended the aircraft to FL120, and later to 10,000ft when fuel reserves permitted. The flight continued and landed without further incident. None of the affected passengers required medical attention. The aircraft had suffered a pressurisation system failure three days earlier on a flight from Canberra to Sydney.

After rectification at Sydney, it flew without incident until this flight. Investigation revealed that the Cabin Outflow Valve and the Equipment Cooling Auto Flow Control Valve were out of adjustment. The Panel Pressurisation Control Mode Selector Switch was also faulty with an intermittent continuity failure. The pilots did not contravene any regulation or company procedure by continuing the flight unpressurised. However, no consideration had been given to any medical problems that any of the passengers may have had, or that could affect their well-being at higher cabin altitudes.

Safety Action

As a result of the incident, the company has issued instructions that an aircraft that fails to pressurise after take-off and does not respond to early corrective action should return to the departure port or divert to the closest suitable airport.