BOEING 737SOUTHWEST AIRLINES CO
Yuma, AZ, USA · 2011-04-01·N632SW
What happened
NTSB summary, verbatimThe Safety Board's full report is available at http://www.ntsb.gov/investigations/reports_aviation.html. The Aircraft Accident Brief number is NTSB/AAB-13/02. On April 1, 2011, about 1558 mountain standard time (MST), a Boeing 737-3H4, N632SW, operating as Southwest Airlines flight 812 experienced a rapid decompression while climbing through flight level 340. The flight crew conducted an emergency descent and diverted to Yuma International Airport (NYL), Yuma, Arizona. Of the 5 crewmembers and 117 passengers on board, one crewmember and one nonrevenue off-duty airline employee passenger sustained minor injuries. The airplane sustained substantial damage; postaccident inspection revealed that a section of fuselage skin about 60 inches long by 8 inches wide had fractured and flapped open on the upper left side above the wing. The flight was conducted under the provisions of 14 Code of Federal Regulations (CFR) Part 121 as a regularly scheduled domestic passenger flight from Phoenix Sky Harbor International Airport, Phoenix, Arizona, to Sacramento International Airport, Sacramento, California.
Photographs
6the aircraft, and what the investigators foundPhotographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.
Probable cause
the Board's determinationthe improper installation of the fuselage crown skin panel at the S-4L lap joint during the manufacturing process, which resulted in multiple site damage fatigue cracking and eventual failure of the lower skin panel. Contributing to the injuries was flight attendant A's incorrect assessment of his time of useful consciousness, which led to his failure to follow procedures requiring immediate donning of an oxygen mask when cabin pressure is lost.
Occurrence sequence
1 stepsNTSB coding · CICTT taxonomy- 1 · Enroute-climb to cruiseAircraft structural failuredefining event
Findings
2 causal · 0 contributing- CAUSEPersonnel issues › Experience/knowledge › Knowledge › Knowledge of procedures — Cabin crew
- CAUSEAircraft › Aircraft structures › Fuselage › Fuselage main structure — Incorrect service/maintenance
Sequence of events
6 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)- 15:40 MSTtakeoffp.3Takeoff, followed by approximately 18 minutes of climb
- 15:58:09 MSTclimbp.3Climbing through FL340, the cabin altitude warning parameter indicated a warning (rapid decompression)
- 15:58-16:03 MSTemergency descentp.3Over the next 4.5 minutes the aircraft descended from FL340 to 11,000 ft (emergency descent)
- about 16:06 MSTdescentp.3After leveling at 11,000 ft for 3.5 minutes the aircraft descended to 9,000 ft
- 16:11:33 MSTdescentp.3Cabin altitude warning deactivated as the aircraft descended through approximately 8,500 ft
- 16:28 MSTlandingp.3Aircraft landed at Yuma
NTSB analysis
from the final reportThe Safety Board's full report is available at http://www.ntsb.gov/investigations/reports_aviation.html. The Aircraft Accident Brief number is NTSB/AAB-13/02. On April 1, 2011, about 1558 mountain standard time (MST), a Boeing 737-3H4, N632SW, operating as Southwest Airlines flight 812 experienced a rapid decompression while climbing through flight level 340. The flight crew conducted an emergency descent and diverted to Yuma International Airport (NYL), Yuma, Arizona. Of the 5 crewmembers and 117 passengers on board, one crewmember and one nonrevenue off-duty airline employee passenger sustained minor injuries. The airplane sustained substantial damage; postaccident inspection revealed that a section of fuselage skin about 60 inches long by 8 inches wide had fractured and flapped open on the upper left side above the wing. The flight was conducted under the provisions of 14 Code of Federal Regulations (CFR) Part 121 as a regularly scheduled domestic passenger flight from Phoenix Sky Harbor International Airport, Phoenix, Arizona, to Sacramento International Airport, Sacramento, California.