Description

On 7 September 2008 a South African Airways Airbus A319 en route from Cape Town to Johannesburg at FL370 received an ECAM warning of the failure of the No 1 engine bleed system. The crew then closed the No. 1 engine bleed with the applicable press button on the overhead panel. The cabin altitude started to increase dramatically and the cockpit crew advised ATC of the pressurisation problem and requested an emergency descent to a lower level. During the emergency descent to 11000 ft amsl, the cabin altitude warning sounded at 33000ft and the flight crew activated the cabin oxygen masks. The APU was started and pressurisation was re-established at 15000ft amsl. The crew completed the flight to the planned destination without any further event. The crew and passengers sustained no injuries and no damage was caused to the aircraft.

The Investigation

An investigation was carried out by the Accident and Incident Investigation Division of the South African CAA. This found that the aircraft had been released to service the previous day with an ADD for the No 1 Engine Bleed System Inoperative and the aircraft to be operated in accordance with the corresponding MEL requirements, which were “that the No.1 engine bleed system was to be selected 'closed' and No 2 engine bleed system was to be selected ‘open’ by means of the press button switches on the overhead panel." The Captain on the last flight of the previous day nevertheless decided to select both No 1 and No 2 engine bleed switches to the ‘open’; position and in the event of an engine bleed system malfunctioning, he planned to isolate the faulty bleed system. An uneventful flight was then made to a night stop for the aircraft.

The next morning, a different crew departed with the No 1 bleed system selected open and the No 2 bleed system selected closed. According to the flight crew, Aircraft Technical Log was only brought to the aircraft 10 minutes prior to departure. They noted the entry that advised that the No.1 engine bleed was faulty and the defect had been subject to ADD action but they stated that they had not configured the system as they “thought that it was already set up……(from) the previous flight the previous day. However, the flight crew failed to notice that the required placard (the ‘INOP” decal) had been fixed at the serviceable No 2 engine bleed system switch position and not at the No. 1 engine bleed system switch position and that in accordance with the incorrect placard, the No 2 engine bleed was selected closed. When failure of the No 1 bleed system was subsequently annunciated en route, the crew response of closing the no 1 bleed left the aircraft with no functioning pressurisation system at all and resulted in the rapid rise of cabin altitude which followed. Only the emergency descent carried out and the simultaneous APU start resulted in the cabin altitude eventually stabilising. The Investigation was not able to establish conclusively whether the placarding of the defect was carried out correctly by maintenance personnel.

In the Final Report on this Serious Incident published on 5 May 2009, the Probable Cause of the occurrence was determined to be the “Failure of the crew to carry out a proper pre-flight inspection leading to the number 1 engine bleed air system being left on and the number 2 engine bleed air system being secured; subsequently the failure of the pressurisation system.”

Two Safety Recommendations were made:

• “It is recommended that South African Airways Flight Operations and Technical issue a briefing notice regarding the importance of strictly adhering to requirements stipulated in the MEL, where failure to do so could adversely affect the safe operation of a flight. It is also recommended that the briefing should include the importance of reading the (Aircraft Technical Log) and cross-checking whether the aircraft configuration agrees with the MEL dispatch conditions.

• Although it is not always practical that the (Aircraft Technical Log) remains in the cockpit at all times as suggested by SAA Flight Operations, it is suggested that (it) be available to the cockpit crew when they start with their pre-flight inspections approximately one hour before departure time.

Related Articles

• Emergency Descent: Guidance for Flight Crews
• Loss of Cabin Pressurisation
• Emergency Communications
• Aircraft Pressurisation Systems
• Minimum Equipment List (MEL)
• Acceptable Deferred Defect
• Aircraft Technical Log
• Defect Assessment
• Captain's Aircraft Acceptance

Further Reading

• The Full Report (CA 12-12 CA 12-12b) of this Investigation by South African CAA.