Incident Overview
During a flight at flight level 370 (FL370), the crew observed that the cabin altitude began to increase. In response, they initiated an emergency descent. The aircraft landed without further incident, and passengers deplaned in a normal manner.
Post-Flight Examination
A subsequent inspection of the aircraft revealed a 9-inch by 18-inch hole in the fuselage, located approximately 3 feet forward of the cargo door. The hole was attributed to a crack that had developed in the skin.
Metallurgical Findings
A metallurgical examination of the failed area determined that the crack was the result of fatigue. The fatigue crack originated from scrape marks present on the inside surface of the skin, immediately adjacent to the crack's origin point. No other contributing factors were noted in the examination.
Operational Response
After the emergency descent, the aircraft landed safely. There were no reports of unusual events during the deplaning process. The crew's actions followed standard procedures for a loss of cabin pressure event.
Investigation Outcome
The investigation identified the root cause as a fatigue crack that began at pre-existing scrape marks on the interior of the fuselage skin. No further causal factors were cited.