Nine facts about Boeing's 737 Classic inspection Service Bulletin

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Nine facts about Boeing's 737 Classic inspection Service Bulletin By

Jon Ostrower  on April 5, 2011 2:27 PM | Permalink | Comments (7) | TrackBacks (0) |
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. 
UPDATE 6:03 PM: Here's my complete story on the service bulletin and here's the full text of the FAA emergency airworthiness directive.
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. Categories: Boeing Tags: 737, Boeing, FAA, Southwest Airlines 0 TrackBacks

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7 Comments By Gustiewing
on April 5, 2011 3:05 PM | Reply

Time for Southwest to get A320s and rapido. In the long term A320NEOs will be ideal. A no brainer really.

By WingBender
on April 5, 2011 6:33 PM | Reply

BA Investor's Boeing shares closed at $73.23 today.

By arcanys outsourcing company
on April 6, 2011 3:47 AM | Reply

This might sound a lot of inconvenience for others but I would like to stress a point that other states airline should undergo the same procedure. Safety regulations shouldn't be scrap due to business matters. We do not want to gamble lives here.

By 4wsqv
on April 6, 2011 4:11 PM | Reply

The photo was taken at Everett's Paine Field. Southwest doesn't offer commercial service there (no one does - yet) but they have a lot of out-sourced maintenance done at B.F. Goodrich’s Aviation Technical Services, at the south end. The north end of course is the home of whats-their-name, you know, the place that makes all those big airplanes.

By Hreotio
on April 7, 2011 10:14 AM | Reply

The inner skin of str 4 was cover by an inspection mandated by AD 2003-08-15 (starting at 45,000 FC) because similar cracks were found after 53,000 FC. See
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/2f60ba76185998a286256d13004f39f1/$FILE/030815.pdf

By iamlucky13
on April 7, 2011 1:43 PM | Reply

So if I understand this right, they came up with this lap joint design as a sub-series because of issues expected at 50,000 cycles with the old design based on either analysis or testing, but now they're seeing issues at 35,000 cycles? That sucks.

I've tried staring at the photos of the damaged part to understand the construction of that joint, but it seems a little funny to me. It looks like the sheet on the bottom of the joint is the one that actually peeled back, hinging at a line of fasteners that I suppose is a stringer?

By 3dmashup
on April 7, 2011 1:46 PM | Reply

VPI studied crack propagation on airframes with tear straps. This paper give you an idea of what a tear strap is and does.

http://scholar.lib.vt.edu/theses/available/etd-082599-211808/unrestricted/etd.pdf

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