ASN Wikibase Occurrence # 266124
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| Date: | Sunday 25 July 2021 |
| Time: | 14:51 LT |
| Type: |  Boeing 737-790 (BDSF) |
| Owner/operator: | Alaska Airlines |
| Registration: | N627AS |
| MSN: | 30794/796 |
| Year of manufacture: | 2001 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | None |
| Location: | 56 nm WNW of Nanaimo, BC -
 Canada
|
| Phase: | En route |
| Nature: | Cargo |
| Departure airport: | Seattle/Tacoma International Airport, WA (SEA/KSEA) |
| Ketchikan International Airport, AK (KTN/PAKT) | |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
An Alaska Airlines Boeing 737-700 operating as flight AS7004, was conducting a cargo flight from Seattle-Tacoma Intl (KSEA), WA to Ketchikan Intl (PAKT), AK, with 2 pilots on board. Shortly after levelling off at FL400, the crew observed a 'Cabin Altitude' annunciation accompanied by the cabin altitude horn. The crew donned oxygen masks, referred to the quick reference checklist, and declared an emergency with Vancouver ATS while beginning an emergency descent. The crew selected manual mode on the Pressurization Mode Selector and observed the cabin pressure improving during the descent. The 'Cabin Altitude' light extinguished when the aircraft passed through FL100 and then leveled at FL90. The crew removed their oxygen masks and after contacting dispatch, returned to KSEA where they landed without incident. There were no reported injuries or damage to the aircraft.
Maintenance found the aft outflow valve was not fully closing in both normal and manual selector modes. The aft outflow valve was replaced, an aircraft pressurization test was successfully completed, and the aircraft was returned to service.
Sources:
TSB
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 30-Jul-2021 17:01 | harro | Added |
| 30-Jul-2021 17:02 | harro | Updated [Narrative] |
Corrections or additions? ... Edit this accident description
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