A Southwest Boeing 737-700, registration N726SW performing flight WN-1685 from Las Vegas,NV to Boise,ID (USA), was enroute at FL390 about 130nm southwest of Salt Lake City,UT (USA) over terrain rising up to above 3000 meters/10.000 feet MSL, when the crew initiated a rapid descent to FL220 due to unstable cabin pressure. The aircraft levelled off at FL220 about 7 minutes after leaving FL390 (average rate of descent 2400 fpm). The cabin pressure stabilized at FL220, the passenger oxygen masks had not deployed, so that the crew continued the flight to Boise maintaining FL220. The aircraft landed safely in Boise about 38 minutes after leaving FL390.

Late Mar 13th 2020 US East Coast time the FAA reported the cabin pressure had gradually decreased in flight. An inspection by the FAA revealed a 12inch/30cm long crack in the crown skin of the aircraft in an area, which was required to be inspected every 1500 hours already. The last inspection of that area had been done 500 flight hours before the occurrence. The FAA is investigating the occurrence, it is too early to tell whether more frequent examinations of these areas will be required.

The airline confirmed the occurrence stating the crew performed an about 6 minute descent from FL390 to FL220, at FL220 the cabin pressure was safe and the crew completed the flight at that altitude. Oxygen masks never dropped. On Friday (Mar 13th) the aircraft was in a maintenance facility at Boise undergoing repairs.

The occurrence aircraft is still on the ground in Boise on Mar 14th 2020.

In 2011 another crack in the fuselage crown caused a sudden loss of cabin pressure, see Accident: Southwest B733 near Yuma on Apr 1st 2011, hole in fuselage, sudden decompression.

https://flightaware.com/live/flight/SWA1685/history/20200309/1610Z/KLAS/KBOI