Federal Aviation Administration (FAA) (Washington) today (April 5) will issue an emergency directive that will require operators of specific early Boeing 737 models to conduct initial and repetitive electromagnetic inspections for fatigue damage. This action will initially apply to a total of approximately 175 aircraft worldwide, 80 of which are U.S.-registered aircraft. Most of the aircraft in the U.S. are operated by Southwest Airlines (Dallas).

The FAA airworthiness directive will require initial inspections using electromagnetic, or eddy-current, technology in specific areas of the aircraft fuselage on certain Boeing 737 aircraft in the -300, -400 and -500 series that have accumulated more than 30,000 flight cycles. It will then require repetitive inspections at regular intervals.

Last November, the FAA published a rule designed specifically to address widespread fatigue damage in aging aircraft. The rule requires aircraft manufacturers to establish a number of flight cycles or hours a plane can operate and be free from fatigue damage. The rule requires aircraft manufacturers to incorporate the limits into their maintenance programs.

The Federal Aviation Administration (FAA) (Washington), with input from the manufacturers and the airlines, is finalizing a new rule to prevent “widespread fatigue damage” (WFD) on airliners. The order requires aircraft makers and airlines to establish the number of takeoff and landing cycles or the number of hours a plane can safely operate in order to lower the risk of fuselage fatigue damage. After the limit is established, the rule will prohibit airlines from flying older aircraft past that point unless an extension is requested and approved.

Here is the full press release by the FAA:

“In a continuing effort to address aging aircraft issues, the Federal Aviation Administration (FAA) has finalized a rule designed to protect most of today’s commercial planes and those designed in the future from structural damage as they age.

The new rule seeks to prevent “widespread fatigue damage” (WFD) by requiring aircraft manufacturers and certification applicants to establish a number of flight cycles or hours a plane can operate and be free from WFD without additional inspections for fatigue. Manufacturers have between 18 and 60 months to comply depending on the particular aircraft type.

Once manufacturers establish these limits, operators of affected aircraft must incorporate them into their maintenance programs within 30 to 72 months, depending on the model of aircraft. After the limit is in the maintenance program, operators cannot fly the aircraft beyond that point unless the FAA approves an extension of the limit.

An airplane’s metallic structures are stressed and can develop cracks when they experience repeated loads such as the pressurization and depressurization that happens on every flight. While airlines regularly inspect aircraft for cracks exceeding a certain size, WFD involves aircraft developing numerous tiny cracks, none of which would have raised concerns individually but which together run the risk of joining up and impairing the structural integrity of the plane.

The new regulation applies to airliners with a takeoff weight of 75,000 lbs. and heavier. It also applies to all transport designs certificated in the future.

The affected models, totaling 4,198 U.S.-registered airplanes, are listed in the rule.

The FAA is working closely with the European Aviation Safety Agency (EASA) and other national authorities to harmonize this rule with their regulations as much as possible. EASA is now developing rulemaking to address WFD, and the FAA participates in that process.”