The UK Air Accidents Investigation Branch (AAIB) has released its findings into a pressurization incident involving an easyJet Airbus A320-251N, registered G-UZEF. The event occurred on 20 April 2025 while the aircraft was operating a scheduled flight from Belfast International Airport (BFS) to Palma De Mallorca Airport (PMI). During the climb, the aircraft failed to pressurize correctly, leading the crew to carry out an emergency descent. The aircraft later continued safely to its destination.
The published report outlines how a cockpit configuration issue following de-icing led to the abnormal pressurization behavior. Although no injuries were reported, the AAIB classified the occurrence as a serious incident due to the potential safety risks involved. The investigation highlights the importance of checklist discipline and situational awareness during high-workload phases of flight. Lessons from the event have already resulted in safety actions by the operator.
Pressurization Issue During Climb
The incident involved EasyJet flight U23011, operated by an Airbus A320neo, which was climbing toward its planned cruising altitude of FL390 when the cabin failed to pressurize as expected. The aircraft’s pressurization system was unintentionally inhibited because the ditching pushbutton had been left selected during cockpit reconfiguration following de-icing. This incorrect configuration prevented the automatic regulation of cabin pressure, causing the cabin altitude to rise steadily as the aircraft continued its climb.
As the cabin altitude increased, cockpit warnings alerted the flight crew to the developing problem, prompting them to initiate an emergency descent to FL200 in accordance with standard procedures. During the descent, the commander identified the incorrectly selected pushbutton and reset it, restoring normal pressurization. After confirming that the system was functioning correctly and the aircraft was stable, the crew climbed back to cruise altitude and completed the remainder of the flight without further incident. The AAIB report stated:
“With the ditching pushbutton selected, the aircraft did not pressurise and the cabin altitude slowly increased as the aircraft climbed to its cruise altitude.”
Crew Response And Emergency Descent
The AAIB classified the investigation as a correspondence inquiry, meaning it was conducted using pilot reports, flight data, and supporting documentation rather than a full on-site field investigation. These types of inquiries are typically used for incidents where no damage or injuries occur, but where there is still clear safety value in understanding the sequence of events. Correspondence investigations allow the AAIB to identify procedural or human-factors issues and share lessons learned across the aviation industry. As such, they form an important part of the UK’s broader aviation safety oversight framework.
Pressurization failures are treated as serious events because reduced oxygen levels at altitude can quickly impair crew performance and passenger well-being if not addressed promptly. In this case, the flight crew’s timely response ensured the safety of everyone on board and prevented further escalation. Once the configuration error was corrected, the aircraft’s systems operated as designed, demonstrating the effectiveness of both the aircraft’s safeguards and standard operating procedures.
The AAIB noted that both EasyJet and Airbus have taken safety actions following the incident. These include raising awareness of the risk and reviewing checklist procedures associated with de-icing and aircraft reconfiguration to reduce the likelihood of recurrence.
How Cabin Pressurization Impacts Passenger Comfort
Higher cabin pressure typically means a more comfortable experience for passengers.
Recovery And Operational Outcome
Similar configuration-related incidents have been recorded across the Airbus A320 family, often during transitional phases such as after de-icing or during abnormal operations. These events reinforce the importance of clear task management and strict adherence to standard operating procedures. Investigators consistently highlight checklist discipline as a critical defense against human error.
The report also contributes to the AAIB’s wider body of correspondence investigations, which are published monthly and used by operators to improve training and safety management systems. Even minor procedural deviations can have significant consequences if left uncorrected.
As airlines continue to refine procedures and training based on such findings, incidents like this serve as valuable reminders of how quickly manageable issues can escalate, and how effective crew actions remain key to maintaining flight safety.
