2023-01 · NASA ASRS report 1962880
C525 flight crew reported loss of Cabin Pressure Control during climb. The flight crew requested priority handling and immediately descended. Oxygen masks were deployed and donned. The flight crew was unable to control the cabin pressure and elected to continue at a lower altitude with a depressurized cabin to destination airport.
Cruising at 28;000 ft.; I noticed an air movement sound and identified a rapid rate of cabin depressurization at 2;100 ft. per minutes as indicted on the cabin pressure gauge. Simultaneously the Captain; noticed the same rate and begin an immediate descent and called for donning of oxygen mask. Due to radio traffic; I was unable to make immediate contact with ATC as the event occurred during change over from ZZZ to Center. Upon contact with Center I notified them we were in a descent; requested priority handling and was unable to honor their level instructions at 25;000 ft. Due to TCAS alert during descent; we had to slow the descent around 25;000 ft. until alert cleared and then we descended to 11;000 ft. During descent; cabin altitude climbed to above 17;000 ft. and the passenger oxygen mask automatically deployed as designed. Upon reaching 11;000 ft. we consulted the checklist and completed all steps as required. With immediate situation; over we verified remaining fuel and terrain clearance and determined we could continue safely to ZZZ1 in a depressurized cabin. We landed safely in ZZZ1 40 minutes later with no other issues.
While in cruise flight at FL280 both Crew Members noticed that the cabin pressure had suddenly started to reduce; both by a noticeable noise of 'rushing air' and the cabin pressure gauge showing the cabin climbing at 2;100 ft./minute. Oxygen masks were donned; I initiated an immediate descent; and the Copilot attempted to make a request for priority handling descent to ATC (Center). Due to frequency congestion the Center Controller wasn't able to hear our initial call; but subsequent attempts clarified our situation. Center Controller told us to stop our descent at FL250 due to a traffic conflict. As I initiated the immediate descent; I had noticed that there was one aircraft that would likely be a conflict so I had already initiated a shallowing of our descent. Our TCAS depiction of the conflicting aircraft turned 'AMBER'; but we were never closer than 1;000 ft. above the other aircraft. as soon as the conflict cleared; we continued the immediate descent to 11;000 ft. The cabin altitude warning light came on during our descent; the cabin overhead oxygen masks automatically deployed (X passenger on board). The cabin altitude never rose above 17;000 ft.; and once we leveled off at 11;000 ft. the cabin stabilized at a 3;000 ft. indication on the gauge and maintained a 3.2 PSI differential. All appropriate checklist items were accomplished and we determined that there was no structural cause (most likely an outflow valve had failed) and ascertained that our passenger had suffered no stress; we elected to continue to destination.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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