What happened
On 07 September 2008, an Airbus A319-131, registration ZS-SFN, was operating a scheduled domestic flight from Cape Town International Airport to O.R. Tambo International Airport. While cruising at 37,000 feet, the cockpit crew received an ECAM warning indicating a failure in the No. 1 engine bleed system. In an attempt to address the issue, the crew closed the No. 1 engine bleed switch. However, this action triggered a rapid increase in cabin altitude.
As the cabin altitude rose sharply, the crew initiated an emergency descent to 11,000 feet. During the descent, the cabin altitude warning activated at 33,000 feet, necessitating the use of oxygen masks. The crew successfully started the Auxiliary Power Unit (APU), which allowed them to re-establish pressurization at 15,000 feet. The aircraft landed safely at O.R. Tambo with no injuries to the 63 people on board and no damage to the aircraft.
The investigation
SACAA AIID investigators examined the maintenance and pre-flight procedures leading up to the incident. The investigation revealed that the aircraft had been dispatched the previous day with a known defect in the No. 1 engine bleed system. Per the Minimum Equipment List (MEL), the No. 1 bleed should have been closed and the No. 2 bleed left open. However, a maintenance technician had incorrectly placed the 'INOP' decal on the No. 2 engine bleed switch instead of the No. 1 switch.
On the morning of the incident, the flight crew received the maintenance defect reports only 10 minutes before departure. The crew assumed the aircraft was already configured according to the MEL requirements from the previous flight. Because they did not verify the actual switch positions against the MEL, they inadvertently left the faulty No. 1 system open and secured the functional No. 2 system.
Findings
- The primary cause was the failure of the crew to perform a proper pre-flight inspection, which resulted in the incorrect configuration of the bleed air systems.
- A maintenance error occurred when the 'INOP' decal was placed on the serviceable No. 2 engine bleed switch rather than the defective No. 1 switch.
- The flight crew failed to cross-check the aircraft's physical configuration against the instructions provided in the MEL and the maintenance defect records.
- The crew's decision to close the No. 1 bleed switch, combined with the already closed No. 2 switch, directly caused the loss of pressurization capability.