What happened
On May 2, 2018, a Raytheon 400 A Nextant 400XT, operating as G-FXAR, was cruising at 38,000 feet en route from Milan-Linate to London Luton when the crew received a Master Caution alert for low cabin pressure. The crew observed that the cabin altitude was climbing rapidly at a rate of approximately 600 feet per minute.
Following standard procedures, the crew initiated a depressurization drill and requested an initial descent to 34,000 feet. However, the cabin altitude continued to rise uncontrollably. This triggered the automatic deployment of oxygen masks in the cabin and manual deployment in the cockpit. During the emergency, the pilot in the left-hand seat experienced difficulty communicating due to a malfunction with the oxygen mask microphone selector, though the crew successfully utilized Crew Resource Management to manage the situation.
After declaring a Mayday, the crew performed a rapid emergency descent, dropping through 16,000 feet and 8,000 feet, before diverting to Geneva. The aircraft landed safely on runway 23 at Geneva Airport with emergency services on standby. There were no injuries to the crew during the incident.
The investigation
An engineering inspection of the aircraft conducted in Geneva revealed that the high-pressure valves on both engines were malfunctioning. The investigation determined that the left valve was likely degraded, while the right valve was clearly damaged. The inquiry also identified that a non-mandatory Service Bulletin (SB 21-2015-01) had been issued by Nextant Aerospace in May 2016 to address reliability issues with these specific valves.
Findings
- The loss of cabin pressure was caused by faulty high-pressure valves which resulted in a loss of pneumatic pressure and airflow.
- The engine type installed on the aircraft was known to have several issues regarding these specific valves.
Safety action
Following the incident, the aircraft underwent the application of Service Bulletin 21-2015-01, which included various tests and an engine run-up to ensure the reliability of the low and high-pressure valves.