Building on last night's post about the criteria for inspection, Boeing has released details about its service bulletin (SB) issued last night that covers 175 737-300s, -400s and -500s.
Here are the quick facts:
- The SB requires inspection of the lower row of fasteners in the lap-joint, along the left and right-hand side of the crown of the aircraft at stringer four between Station 360 and 908, making the area under scrutiny about 50ft long.
- This SB applies to line numbers 2553 through 3132, which were delivered between 1993 and 2000, which had a frame tear strap spacing of 20 inches.
- Of the 579 aircraft produced, only about 175 have 30,000 cycles or more.
- Inspections must take place within 5 days on a portion of the 175 that have 35,000 cycles or more.
- Inspections will be required within 20 days of the remaining balance of the 175 aircraft with between 30,000 and 34,999 cycles.
- Around 80 of the 175 are in the US, with the majority flying with Southwest Airlines.
- Inspections will be repeated every 500 cycles until a more permanent solution can be identified as a result of the NTSB investigation.
- Line numbers 292 through 2552 had a different lap joint design, which Boeing says included a frame tear strap spacing of 10in. That design already fell into a lap-joint modification program that came in to effect for those aircraft over 50,000 cycles.
- For line numbers 2553 through 3132, Boeing said it anticipated cracks in this area of the fuselage, but not until 60,000 cycles or more.