What happened
On 14 June 2019, an Airbus A319, registration 9V-TRB, was descending from 36,000 feet toward Singapore Changi Airport when the flight crew noticed a sudden change in cabin pressure. As the aircraft descended through 29,000 feet, the cabin altitude began to rise steadily, eventually reaching approximately 13,936 feet.
Upon receiving a cabin pressurization warning, the crew initiated an emergency descent. The pilots donned oxygen masks and increased the descent rate to roughly 5,300 feet per minute by deploying speed brakes. The crew declared a PAN-PAN signal to Air Traffic Control and successfully brought the aircraft down to 9,000 feet before landing safely at Changi Airport. There were no injuries to the 129 people on board and no damage to the aircraft.
The investigation
Investigators examined the aircraft's airframe, door seals, and the cabin pressurization system. While ground tests of the system and safety valves showed no immediate anomalies, the investigation focused on the two Cabin Pressure Controllers (CPCs) used on the aircraft.
Upon removal and examination by the manufacturer, both CPCs showed signs of contamination and corrosion. The analysis determined that the active controller (CPC 2) had processed a corrupted Landing Field Elevation (LFE) value. This corrupted data triggered a procedure intended for landing at high altitudes, causing the outflow valve to open excessively and drive up the cabin altitude.
Findings
- The primary cause of the excessive cabin altitude was the corruption of the LFE value within the active CPC.
- The corruption of this data was likely caused by a fatigue solder joint on the CPC circuit board.
- The aircraft's processing logic functioned as designed, but it was unable to detect that the LFE input had been corrupted by the hardware failure.
- Similar incidents involving corrupted LFE values have been documented in previous investigations involving other operators.