Created Friday, Jul 30th 2021 20:06Z, last updated Friday, Jul 30th 2021 20:06Z
An Alaska Airlines Boeing 737-700, registration N627AS performing freight flight AS-7004 from Seattle,WA to Ketchikan,AK (USA) with 2 crew, was enroute at FL400 about 90nm northwest of Vancouver,BC (Canada) when the crew received a "Cabin Altitude" warning and the cabin altitude horn sounded. The crew donned their oxygen masks and initiated an emergency descent. The crew selected the pressurization selector to manual. When the aircraft descended through 10,000 feet the cabin altitude indication ceased, the aircraft levelled at 9000 feet. The aircraft returned to Seattle for a safe landing about 85 minutes after departure.
The Canadian TSB reported maintenance found the outflow valve did not fully close in both automatic and manual operation. The valve was replaced.
