The US FAA has finalised a rule it proposed in September 2009 requiring structural inspections of Boeing 737 classics for cracks after Southwest Airlines experienced an in-flight skin rupture and depressurisation on a 737-300.
As previously reported by ATI and Flightglobal, the incident occurred in July 2009 while the aircraft was enroute from Nashville to Baltimore. The aircraft landed safely in Charleston, West Virginia with a 43cm (17in) by 20cm hole in the skin on the upper section of the rear fuselage.
The inspections required in the final rule cover Boeing 737-300/400/500 series aircraft, and must be completed before the accumulation of 35,000 flight cycles or within 500 flight cycles of the rule's 16 February effective date. If no cracking is found, repetitive inspections are required at certain intervals not to exceed 500 flight cycles.
At the time of the Southwest incident, the affected aircraft had accumulated 42,569 cycles.
Carriers can be exempt from the continued inspections if they have installed an external doubler in a specific area on the fuselage outlined in a Boeing service bulletin issued in September of 2009.
FAA estimates 135 aircraft are affected by the new rulemaking.