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1st of April 2011

A Boeing 737-3H4 was operating a scheduled domestic flight from Phoenix (Arizona, USA) to Sacramento (California, USA), on this day in aviation history in 2011, on board a crew of 5 and 117 passengers.

The aircraft in Yuma (Az) after landing, the failed section of the fuselage is visible on the aircraft crown, just aft of the overwing exit, with the yellow arrow (Source & © NTSB)

The aircraft was cruising at flight level 340 (~34.000 feet / ~10.360 meters) after a normal take-off and climb when just before 15.00 local time when an unidentified sound was heard and a rapid decompression occurred. 2 seconds later the captain announce that a loss of pressurisation had occurred and called for oxygen masks to be selected to "on", while an emergency descent was initiated. During the emergency descent, a cabin crew member of the cabin crew lost consciousness while performing his duties without putting on an oxygen mask. An off duty airline employee rushed to the aid of the crewmember but also lost consciousness. Both suffered minor injuries and regained consciousness while the aircraft descended. The oxygen masks in the cabin had deployed and passengers were using them. ATC was contacted by the captain and an emergency was declared and a lower altitude was requested. ATC provided the necessary clearances and the aircraft descended to 11.000 feet ( 3350 meters) within 5 minutes of the onset of the emergency. A few minutes later the cabin crew started providing the flight crew with condition updates from the cabin. One of these reports described a 2-foot hole in the fuselage, as well as a broken nose for the cabin crewmember that had lost consciousness. A further descent was requested, and the aircraft was cleared down to 9000 feet (2700 meters).

The crew then requested vectors to the nearest suitable airport, which was Yuma, Arizona, USA. 31 minutes after the decompression the aircraft landed without further incident at Yuma. All passengers disembarked via the aircraft stairs. Besides the cabin crew member that fainted, and broke his nose and the off duty employee that attempted to come to his aid and got a cut above the eye, none of the occupants of the aircraft sustained any injury.

A post-flight inspection of the aircraft revealed a 60" x 8" (50cm x 20 cm) wide piece of aircraft skin had cracked open. Some of the adjacent (sub) structures also got damaged in the incident. Diagram of fuselage lapjoint construction in

the failure area, (source & © NTSB)

The National Transportation Safety Board launched an investigation and in their report provide an extensive description of the affected structure and the manufacturing process of the aircraft fuselage. The report is available by clicking here. They determined 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 the flight attendant was the 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.

Close up of the failed fuselage (Source & © NTSB)

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