Incident: Portion of Boeing 737's upper fuselage skin (about eight by 60 inches) blew out at 34,000 feet during a scheduled flight on April 1, 2011. Original post on Disaster-Wise is here. (Photo, NTSB)
Location: Southwest Flight 812 was enroute from Phoenix to Sacramento when a portion of fuselage skin blew out, causing rapid decompression. Airplane made an emergency descent and landed safely at Yuma, AZ.
Effects: Two injured: one passenger, one employee. (Due to delay in donning oxygen mask, a flight attendant fell unconscious while standing.)
Final report: The NTSB's probable cause report, published September 2013, is linked here.
Probable cause: Flaw during manufacturing, causing failure along rivet lines. Forensic examination of the fatigue fracture indicated that the "fuselage crown skin panel" involved had been attached at a Boeing factory, and then removed for rework before the airplane was delivered. Poor joining techniques at the factory during this rework (eg, oversized holes and poor riveting), followed by thousands of pressurization cycles, led to micro-fractures and failure. Due to the passage of time, documentation was no longer available from Boeing to show exactly how, or at which facility (Wichita KS or Renton WA), the error happened.
Lessons: (1) Need for better quality control when rework is done in the factory. (2) Aircrew should don their oxygen masks at the first sign of depressurization, rather than attempting to carry out other emergency duties first. This is because loss of consciousness can come very quickly.