The FAA is issuing an emergency airworthiness directive (AD) on April 5 requiring operators of specific early Boeing 737 models to conduct initial and repetitive eddy-current electromagnetic inspections for fatigue damage.
According to the FAA, the inspections 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.
The FAA’s decision to issue the emergency AD follows investigation by the National Transportation Safety Board and the FAA of an April 1 incident in which a roof panel in a Southwest Airlines Boeing 737-300 ruptured while the aircraft was cruising at 33,000 feet en route between Phoenix, Arizona and Sacramento in California.
The 737’s passenger cabin depressurized and the pilots performed an emergency descent to 11,000 feet in four and a half minutes. The aircraft subsequently landed safely at Yuma, Arizona. Two people on board the aircraft, a flight attendant and a passenger, suffered minor injuries which did not require hospitalization.
Southwest subsequently has performed inspections on its 79 oldest or highest-flight-cycle 737-300s and reportedly has found small sub-surface cracks in the fuselage skins of three aircraft. The carrier operates a total of 173 737-300s and at least 94 of them are not subject to the new emergency AD.
“Safety is our number one priority,” says U.S. Transportation Secretary Ray LaHood. “Last Friday’s incident was very serious and could result in additional action depending on the outcome of the investigation.”
“The FAA has comprehensive programs in place to protect commercial aircraft from structural damage as they age,” says FAA Administrator Randy Babbitt. “This action is designed to detect cracking in a specific part of the aircraft that cannot be spotted with visual inspection.”
Tomorrow’s emergency AD 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. (A flight cycle is a complete flight, from take-off to landing). The agency will then require repetitive inspections of these aircraft 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.