FAA Issues Emergency Airworthiness Directive

Emergency airworthiness directive (AD) 2011-08-51 has been issued for owners and operators of The Boeing Company Model 737-300, -400, and -500 series airplanes.

This emergency AD was prompted by a report indicating that a Model 737-300 series airplane experienced a rapid decompression when the lap joint at stringer S-4L between body station (BS) 664 and BS 727 cracked and opened up. Investigation showed that the cracking was located in the lower skin at the lower row of fasteners. The airplane had accumulated 39,781 total flight cycles and 48,740 total flight hours. This condition, if not corrected, could result in an uncontrolled decompression of the airplane. Because the lap joint and tear strap spacing configuration is the same on Model 737-400 and -500 series airplanes, these airplanes may be subject to the identified unsafe condition.

The FAA reviewed Boeing Alert Service Bulletin 737-53A1319, dated April 4, 2011. The service bulletin describes procedures for external eddy current inspections of the lap joints at stringers S-4R and S-4L, along the entire length from body station (BS) 360 to BS 908. If a crack indication is found, the service bulletin specifies either confirming the crack by doing internal eddy current inspections, or repairing the crack. As an alternative to the external eddy current inspections, the service bulletin provides procedures for internal eddy current and detailed inspections for cracks in the lower skin at the lower row of fasteners at stringers S-4L and S-4R. The service bulletin specifies contacting Boeing for crack repair instructions.

Differences Between This AD and the Service Information

The service bulletin specifies to contact the manufacturer for instructions on how to repair certain conditions, but this AD requires repairing those conditions in one of the following ways:

• In accordance with a method that we approve; or

• Using data that meet the certification basis of the airplane, and that have been approved by the Boeing Commercial Airplanes Organization Designation Authorization (ODA) whom we have authorized to make those findings.

This AD applies to The Boeing Company Model 737-300, -400, and -500 series airplanes, certificated in any category, as identified in Boeing Alert Service Bulletin 737-53A1319, dated April 4, 2011.

For the full description visit rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/77979606b642117286257869006afb63/$FILE/2011-08-51_Emergency.pdf