Synopsis
On 14 June 2019 at about 2137 hours Singapore local time, an Airbus A319, registration 9V-TRB, operated by Scoot, experienced a slow increase in cabin altitude while descending through flight level 290. The flight crew carried out an emergency descent to 9,000 feet. The aircraft subsequently landed at Singapore Changi Airport without further incident. There were no injuries to any persons and no damage to the aircraft. A PAN-PAN was declared and the flight crew used the oxygen system. The occurrence was classified as an incident.
History of the Flight
The flight departed Clark, Philippines at about 1900 hours for Singapore. The Pilot-In-Command was the pilot flying, and the First Officer was the pilot monitoring. At 2134 hours, the aircraft began its descent from cruise level FL360. During the descent to FL320, the PIC noticed a change in cabin pressure in her ears. The flight crew observed via the ECAM CAB PRESS page that the cabin altitude was increasing through 8,500 feet at a rate of about 550 feet per minute. They responded by increasing the rate of descent to 4,000 feet per minute. At 2137 hours, after requesting further descent from ATC, the cabin pressurisation warning activated when cabin altitude exceeded 9,550 feet. The crew immediately donned oxygen masks and followed the Cabin Pressure/Excess Cabin Altitude checklist. They deployed speed brakes, increasing the descent rate to about 5,300 feet per minute, and the FO declared PAN-PAN. The highest cabin altitude observed on ECAM was about 13,500 feet, though FDR data recorded a maximum of 13,936 feet. The passenger oxygen masks did not deploy automatically (which occurs at 14,000 ft) and were not manually activated. The aircraft descended below 10,000 feet, the crew removed their masks, and the cabin crew performed post-decompression duties. The aircraft landed at 2202 hours.
Aircraft Information
The aircraft was an Airbus A319 equipped with two IAE V2500 engines, registered 9V-TRB. The cabin pressurisation system includes two cabin pressure controllers (CPC1 and CPC2), with only one operating at a time. During the incident, CPC2 was in control. The outflow valve is driven by an actuator with three motors: two for automatic operation and one for manual. The CPC in automatic mode regulates cabin altitude to a maximum of 8,000 feet. The system was in automatic operation throughout the incident.
Analysis
The investigation determined that the excessive cabin altitude was caused by the uncommanded closure of the outflow valve. This resulted from a failure in the CPC2 autopilot-mode motor drive due to a fatigue solder joint at a wiring connection on the CPC2 board. The fatigue solder joint had been reworked previously. No anomalies were found in the general airframe structure or door seals.
Conclusions
The excessive cabin altitude resulted from an uncommanded outflow valve closure due to a fatigue solder joint in CPC2. There were no injuries or aircraft damage.