The FAA is requiring U.S. airlines operating 285 older Boeing 737 Classic jets to make regular inspections for widespread metal fatigue in the aft fuselage skins and to replace some skin panels after 53,000 flight cycles of takeoffs and landings.
The Federal Aviation Administration (FAA) is requiring U.S. airlines operating 285 older Boeing 737 Classic jets to make regular inspections for widespread metal fatigue in the aft fuselage skins and to replace some skin panels after 53,000 flight cycles of takeoffs and landings.
New FAA directives published Thursday make mandatory the recommendations in a special Boeing service bulletin sent last June to airlines operating the affected 737s, which are all at least 18 years old.
Boeing concluded that at points where the aft fuselage skin is chemically milled to create pockets of thinner-gauge metal, the skin is subject over time to widespread metal fatigue — resulting in thin cracks in hidden parts of the aluminum skin that may not be detected during routine airplane inspections.
“As an airplane ages, widespread metal fatigue will likely occur, and will certainly occur if the airplane is operated long enough without any intervention,” the FAA directives state. “Without intervention, these cracks will grow, and eventually compromise the structural integrity of the airplane.”
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The new FAA instructions update a 2009 directive issued after a hole opened in the fuselage of a Southwest 737 flying from Nashville, Tenn., to Baltimore, causing a rapid decompression of the passenger cabin. The plane landed safely and no one was hurt.
The fuselage tear in that incident was attributed to local metal fatigue that caused the aluminum skin to separate along the edge of a chemically milled pocket.
Since then, the FAA directives state, additional cracks were found in 737 aft fuselage skin panels as well as cracks at fastener holes where the panels are spliced together, leading to the conclusion that the metal-fatigue issue is more widespread.
The new safety directives go beyond the previously ordered inspections to add mandatory modifications, including replacement of some skin panels.
The FAA estimates that it will cost U.S. airlines more than $40 million to complete the inspections on all 285 airplanes. Replacing the skin panels will cost up to an additional $50 million, the FAA estimates.
The condition addressed in the FAA directive was not the cause of a separate 2011 incident, when a 5-foot-long hole ripped open in the roof of a 737 Classic during another Southwest Airlines flight, this time out of Phoenix.
In that case, a National Transportation Safety Board investigation determined that it was caused not by aging metal but by “bad workmanship” during assembly of the airplane.
Information in this article, originally published May12, 2016, was corrected May 13, 2016. A previous version of this story incorrectly stated that the fuselage cracks addressed by the new FAA directives occurred along a lap joint. In fact they occur at the edges of areas of the skin that had been thinned through chemical milling. The separate and unrelated incident in 2011 was a lap joint tear.