The discovery of cracks in the pickle forks of some 737NG aircraft has raised major concerns. Cracks in a structural component designed to be safe for the life of the aircraft, or 90,000 cycles, is serious. Boeing, in modifying some older 737NGs for cargo conversion, discovered cracks in aircraft with only about 33,500 flight cycles, or about 1/3rd of the expected life. There are four pickle forks that hold the wing to the fuselage, so a failure could have catastrophic results if a crack was to propagate into a component failure.
The FAA has issued an airworthiness directive to inspect Boeing 737NG aircraft with more than 22,600 cycles within a year, and for aircraft with more than 30,000 cycles within one week. Inspections can be completed by borescope without a major teardown of the airframe, and will likely be conducted overnight by most airlines. Of course, where cracks have been found, replacement will be necessary, which, given the need to tear the aircraft down to its basic structure as in a D-Check, and that substantial hangar time cannot be inexpensive.
With most narrow-body aircraft flying about 3,000-3,500 cycles annually, problems seem to be emerging on aircraft more than 11 years old. Given that there are thousands of 737NGs in service, a major problem would be costly for Boeing.
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