History of the Flight
The flight was a scheduled commercial service from Belfast Aldergrove to Palma de Mallorca, staffed by a commander and a co-pilot undergoing training. The aircraft had arrived late from its previous flight. The commander observed ice on the wings, fuselage, and stabiliser, and decided de-icing might be required. The crew configured the aircraft for de-icing using the Quick Reference Handbook. The de-icing crew performed a tactile check and reported de-icing was unnecessary. During reconfiguration, the crew omitted to turn off the ditching pushbutton.
The aircraft departed with the co-pilot as pilot flying. After reaching cruising altitude FL390, the crew noticed the cabin altitude rising. The commander announced “oxygen masks on, 100%” and declared an emergency descent. The commander took over, initiated the descent, and a MAYDAY was declared. The Electronic Centralised Aircraft Monitoring (ECAM) system sounded the cabin altitude warning. During the descent, the commander set annunciator lights to bright and observed the ditching pushbutton illuminated. He deselected it, and the pressurisation returned to normal. The aircraft levelled at FL200. Following analysis, the crew decided to continue to Palma, climbing to FL370 without further incident.
Recorded Information
Data from the flight data recorder and cockpit voice recorder showed that at 0453 hrs the outflow valve moved from fully open to fully closed and remained closed. After takeoff at 0523:30, the cabin altitude increased progressively. At 0547:14, while at FL390, the cabin altitude exceeded 9,000 ft. The crew donned oxygen masks, and the autopilot was set to FL100. The maximum recorded cabin altitude was 10,304 ft. At 0551:57, after the ditching pushbutton was deselected, the outflow valve opened to 12% and the cabin altitude began to decrease. The cabin pressurisation warning reset approximately 90 seconds later.
Aircraft Systems
The Airbus A320 is equipped with an automatic cabin pressurisation system. The ditching pushbutton, located on the overhead panel, is guarded and closes the outflow valve and pack control valves when selected. It is used to minimise water ingress during a ditching event. When selected, the aircraft cannot pressurise. There is no direct ECAM indication of the ditching pushbutton position.
Safety Action
The operator and the manufacturer have taken safety action to raise awareness of the event and to amend the de-icing checklist.