Zurich, Switzerland: Swiss International Air Lines has come under withering scrutiny after a federal safety investigation found the carrier failed to act on an eight-year-old aircraft safety warning, contributing to a serious in-flight pressurisation failure on a transatlantic flight in 2024.
The Swiss Transportation Safety Investigation Board (STSB) released its final report this month, saying the airline’s inaction was “incomprehensible from a safety perspective,” after a faulty component on an Airbus A330 forced pilots to execute an emergency descent and divert back to Zurich Airport in September 2024.
On September 13, 2024, an Airbus A330 registered HB-JHI operating flight LX18 from Zurich to Newark Liberty International Airport encountered a critical pressurisation problem shortly after take-off. During ascent, the aircraft began losing cabin pressure due to a defective component within the pressurisation system, a “skin check valve” which failed to seal properly.
Although both outflow valves indicated “fully closed,” the aircraft was unable to build sufficient differential cabin pressure. According to the STSB report, cockpit instruments showed inadequate pressurisation despite normal system settings.
Cockpit crews donned oxygen masks, manually deployed passenger oxygen systems, and initiated an emergency descent at approximately 5,000 feet per minute before returning safely to Zurich. All 205 passengers and 12 crew members evacuated normally, and no injuries were reported.
The STSB’s investigation found that the root cause of the pressurisation failure was a mechanically compromised skin check valve that had not been replaced in over eight years, despite Airbus issuing a service bulletin in 2016 recommending its earliest possible replacement and regular inspections every 24 months.
The manufacturer’s bulletin identified that the original valve design was prone to hinge wear, vibration damage and spring failure, all of which could lead to air loss and potential depressurisation events during flight. European aviation regulators and maintenance manuals require that such service bulletins be carefully considered by operators to ensure fleet safety.
Investigators noted that the defective valve on the SWISS aircraft remained in service far beyond its recommended inspection and replacement interval, even after being removed and inspected multiple times without upgrading to the redesigned part. The report concluded that this prolonged delay in corrective maintenance directly contributed to the in-flight incident.
In its final recommendations, the STSB urged the European Union Aviation Safety Agency (EASA) to mandate the skin check valve replacement on all applicable Airbus A330 and A340 aircraft via a formal Airworthiness Directive rather than relying on voluntary compliance with service bulletins.
The board cautioned that gradual decompression events can elude crew awareness in early stages, increasing risk if they occur at cruising altitudes.
SWISS International Air Lines, part of the Lufthansa Group, had not issued an immediate public response, and the airline had not yet provided a formal comment in response to the STSB’s final report.
