The FAA has finalized a rule addressing more than 4,000 U.S.-registered aging commercial aircraft with a takeoff weight of 75,000 pounds or more, certified after 1957 and operated under FAR Parts 121 or 129. Aircraft manufacturers and certification applicants must now set a number of flight cycles (or hours) that such aircraft can be operated and remain free of widespread fatigue damage (WFD) without additional inspection. They have 18 to 60 months (from Jan. 14, 2011) to comply, depending on aircraft type. 

The rule takes effect for older designs such as Airbus A300/A310s, Boeing 727s, 737-100s/-500s, all 747s (except the -400 and the new -8), Lockheed L-1011s and McDonnell Douglas DC-8s, DC-9s, DC-10s and MD-80s, in July 2012. Newer models, such as Airbus A380s, some Boeing 777s and Embraer E170/190s, must comply by January 2016. Operators of affected aircraft must incorporate the limits in maintenance programs within 30 to 72 months, according to model. Thereafter, they may not fly the aircraft beyond prescribed limits unless the FAA approves an extension.

The rule, designed “to protect most [current] commercial planes and [future designs] from structural damage as they age,” comes almost 25 years after an Aloha Airlines Boeing 737 suffered a major structural failure. In that April 1988 accident, an 18-foot section of complete fuselage section above the floor level tore away and the event became a textbook example of the results of WFD. The accident led to the establishment of the industry-wide international airworthiness-assurance working group involving regulators, airlines and aircraft manufacturers. 

Since 1988 the FAA has issued about 100 WFD-related Airworthiness Directives, of which about 25 percent it considered “too urgent” for public scrutiny and response as regulators mandated aging-airframe inspections. The majority of the ADs have been superseded to expand the checks, or require modifications, because inspection proved insufficient to preclude WFD. The FAA defines WFD as involving “numerous tiny [structural] cracks, none of which would raise concern, but which together run the risk of joining up and impairing structural integrity.”

The FAA is working closely with the European Aviation Safety Agency (EASA) and other national airworthiness authorities to harmonize this new rule “as much as possible” with their regulations. The EASA is now developing WFD rulemaking.