Flight Details
Aircraft Type: Bombardier CRJ-900 (CL-600-2D24) Operator: Lufthansa CityLine (for Lufthansa) Registration: D-ACNX Flight Number: LH1220 Route: Frankfurt am Main Airport (FRA), Germany to Salzburg Airport (SZG), Austria Date of Incident: 22 April 2025 Total Occupants: Not publicly disclosed; typical CRJ-900 capacity between 76–90 passengers Weather Conditions: Clear air, routine departure; no meteorological influence reported
Introduction
On 22 April 2025, for the second time within 24 hours, Lufthansa CRJ-900 aircraft D-ACNX was forced to return to Frankfurt due to a cabin pressurisation fault—this time during the initial climb phase of flight LH1220 to Salzburg. The aircraft had previously aborted a flight the day before (LH1390) following cockpit noise and suspected pressurisation issues linked to a forward door. After overnight maintenance, the aircraft was cleared for return to service. However, during the subsequent Salzburg sector, while climbing through FL250, a new pressurisation anomaly occurred, prompting another return to base.
The aircraft landed uneventfully on runway 25C approximately 30 minutes after departure and was taken out of service for extended inspection and rectification.
Sequence of Events
Flight LH1220 departed Frankfurt’s runway 18 on schedule and began a standard climb profile towards its cruising altitude en route to Salzburg. Upon passing FL250 (25,000 feet), the flight crew noted abnormal pressurisation readings.
The symptoms were consistent with:
Inability to maintain cabin altitude within limits Possible unexpected climb of cabin altitude, triggering ECAM/CAS warnings Autopilot compensation or warnings for pressure deviation Cabin crew alerting the flight deck to physical symptoms (ear pain, cabin noise, temperature anomalies)
The cockpit crew discontinued the climb, levelled off, and coordinated with ATC for an expedited return to Frankfurt. The aircraft landed safely on runway 25C and taxied to a remote stand for technical inspection.
No emergency was declared, but the flight was prioritised for return.
Crew & Communication
The crew acted in line with Lufthansa CityLine and Bombardier procedures for pressurisation system malfunction, including:
Monitoring Cabin Pressure Acquisition Module (CPAM) output Executing QRH checklists for Cabin Pressure Abnormal or Pressurisation System Failure Coordinating with cabin crew for passenger condition reports Advising ATC of intent to return and confirming operational status Preparing for a potential overweight landing (if applicable)
Cabin crew monitored passengers for signs of discomfort or hypoxia, although there were no reports of decompression, oxygen mask deployment, or medical intervention.
Aircraft Systems & Technical Analysis
This was the second incident involving CRJ-900 D-ACNX in less than 10 hours, with both events relating to cabin pressurisation anomalies:
The first incident (LH1390 on 21 April) involved strong cockpit noise and suspicion of pressurisation imbalance due to a potentially faulty or unseated door seal The second incident (LH1220 on 22 April) occurred post-maintenance, suggesting a deeper systemic or component-level issue
Key components involved in pressurisation control include:
Outflow valve (modulates cabin pressure) Cabin pressure controllers and altitude sensors Seals and structure around pressurised doors Environmental Control System (ECS) bleed air supply integrity
Given the recurrence, a door seal fault alone is unlikely to be the sole cause. This points to possible:
Pressure controller calibration drift Sensor mismatch or faulty CPAM input Outflow valve malfunction or electrical actuator fault Residual fault from previous incident not fully resolved
The aircraft was grounded for over 31 hours following the second return, during which it underwent:
Cabin pressurisation ground tests using external air sources Leak testing of fuselage and door structures Functional tests of cabin altitude and pressure controllers Inspection of the ECS air routing and valve actuation Full BITE (Built-in Test Equipment) data extraction from avionics and environmental systems
Only after a dedicated test flight confirming system integrity was the aircraft cleared to return to commercial service.
Passenger Experience & Cabin Conditions
The return was uneventful from the passengers’ perspective, with no reports of discomfort or panic. Passengers were likely advised via PA systems of a technical return, with cabin crew ensuring passengers remained seated with seatbelts fastened.
There were no reports of unusual noise, smoke, or discomfort beyond the crew-reported cabin pressure concern.
Passengers were rebooked or accommodated on alternate Lufthansa flights to Salzburg.
Emergency Response & Aftermath
No ground emergency services were deployed, as the situation remained controlled. However, airport operations were notified due to the aircraft’s recent repeat technical event history.
Maintenance teams reclassified the aircraft as non-dispatchable pending confirmation of system rectification. Lufthansa Technik coordinated deeper structural and avionics inspection, beyond the initial seal and door checks conducted after the first incident.
Investigation Status
As the event involved no injuries or direct safety compromise, a regulatory investigation is unlikely. However, Lufthansa and CityLine’s Maintenance Control Centre (MCC) and Safety Oversight Units will internally investigate the recurrence and:
Audit the initial post-return maintenance procedures Review system history for repeated BITE entries related to pressurisation Scrutinise technician sign-offs and component test logs Assess whether deeper systemic or design issues are involved
Root Cause & Contributing Factors (Preliminary)
Primary Cause:
Cabin pressurisation system malfunction, potentially involving outflow valve performance or electronic control input discrepancy.
Contributing Factors:
Incomplete rectification of earlier pressurisation-related fault Potential interaction between pressurisation and ECS sensor logic Possible door sensor or structural alignment issues affecting pressure retention under load
Safety Recommendations & Industry Impact
This repeat event reinforces several operational insights:
Importance of comprehensive follow-up after any cabin pressurisation anomaly, especially when structural or seal integrity is suspected Need for multi-system diagnostics, not solely mechanical component inspection Value of extended ground test pressurisation cycles and test flights before return to service on suspect airframes CRJ operators should review historical trends in outflow valve control logic and door sensor system alerts, especially on aging regional fleets
Conclusion
Lufthansa’s CRJ-900 D-ACNX experienced a second pressurisation-related air turnback within a 10-hour window, indicating a deeper or intermittent issue beyond superficial door seal failure. The decision to return mid-climb on LH1220 was appropriate and timely, and the extended ground time for diagnostics demonstrates Lufthansa’s caution in handling potential system reliability risks. This case highlights the intricate balance between aircraft systems, structural integrity, and fault isolation in modern regional jet operations.
Disclaimer
This article is based on publicly available information and reports at the time of writing. While every effort has been made to ensure accuracy, we cannot guarantee the completeness of the information provided.
If you are the rightful owner of any referenced content or images and wish them to be removed, please contact takedown@cockpitking.com.
