Southwest B733 near Yuma on Apr 1st 2011, hole in fuselage, sudden decompression

Last Update: September 27, 2013 / 13:24:18 GMT/Zulu time

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Incident Facts

Date of incident
Apr 1, 2011

Classification
Accident

Airline
Southwest Airlines

Aircraft Type
Boeing 737-300

ICAO Type Designator
B733

The NTSB released their final report concluding the probable causes of the accident were:

The National Transportation Safety Board determines that the probable cause of this accident was the 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.

The NTSB analysed that the crew response, Captain (56, ATPL, more than 17,000 hours on type) and First Officer (51, ATPL, more than 6,350 hours on type), was timely and effective, no crew action influenced the separation of the fuselage crown skin.

However the lead flight attendant attempted to make an announcement after the decompression which caused him to lose consciousness and resulted in a nose fracture. The NTSB stated: "His decision to make the call or P/A announcement before obtaining oxygen was inconsistent with Southwest Airlines training materials, which clearly indicated that flight attendants should first obtain oxygen and secure themselves in the event of a decompression." and continued that the flight attendant most likely incorrectly assessed the available time of useful consciousness.

Laboratory examination revaled that material properties did not contribute to the skin fracture. However, a breakdown in the lap joint sealant between upper and inner surface of the upper doubler started fatigue cracking at that lap joint, which started within 1500 cycles after production of the aircraft leading to the fracture after a total of 38,261 cycles since new. "The NTSB concludes that the fatigue cracking at rivet hole 85 began approximately when the airplane entered service."
Incident Facts

Date of incident
Apr 1, 2011

Classification
Accident

Airline
Southwest Airlines

Aircraft Type
Boeing 737-300

ICAO Type Designator
B733

This article is published under license from Avherald.com. © of text by Avherald.com.
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