FAA investigates cracks on older 737s
 

FAA launches probe after in-flight incident reveals 12-inch crack on 737 jet

(Reuters) - The U.S. Federal Aviation Administration (FAA) said on Friday it has begun a probe following an in-flight incident involving an older 737 aircraft manufactured by Boeing Co (BA.N) and flown by Southwest Airlines (LUV.N).

The FAA said the aircraft was en route to Boise, Idaho, from Las Vegas on Monday and experienced a gradual loss of cabin pressure at one point before reaching the destination without any injury to the passengers.

An initial inspection of the aircraft by the FAA revealed a 12-inch crack on the crown skin in an area that already requires inspections every 1,500 flight cycles.

The Wall Street Journal reported the aviation safety regulator was investigating potential structural problems affecting hundreds of Boeing 737 jets.

"The aircraft was taken out of service and is currently in maintenance receiving repairs," Southwest said in a statement.

More lap joint problems?

Makes me think about Aloha, they also had an issue with crown skin...

I wonder if the increased length of fuselage on many later generation airframes might be a factor in this ?

More likely that the hoop stress from pressuization is the culprit across a corroded/damaged area (wear-out mode)

I assume this was an NG because that's all SWA flies right now.

The areas I'm aware of where large crown skin cracks have occurred are underneath the vertical stabilizer fairings where a rubbing condition can create damage and a stress concentration (I believe this is under an AD-required inspection program, but couldn't quickly find the AD - possibly I'm confusing an issue on another model), at chem-milled steps in the crown skin panels (AD 2013-08-16), and in the areas around some STC-installed inflight entertainment system antenna cutouts (AD 2014-03-19), which have typically been installed in the middle part of the fuselage where crown skin loads are high. I'm assuming this was not a lap splice issue because the report said the crack was in the crown skin. There is no lap joint at the crown. I have not seen anything specific yet related to this report, but the fact that the pressurization system couldn't keep up and it was reported as a 12 inch crack makes me think it was a chem-mill pocket crack that turned the corner of the pocket and opened a flap, which is what the design is intended to do if a crack occurs. I'm guessing, though.

Perhaps this TV report is relevant. I have no first hand opinion on the content, I offer it as it was presented to me a few days ago....

AVHerald reports it to be a -700, N726SW

The report that introduced an AD in 2011, five foot long, Southwest found five other aircraft with issues. DAR, your video seems it may have been produced as a result of this incident, content is somewhat prescient given where we stand with the MAX today.

https://www.ntsb.gov/investigations/...ts/AAB1302.pdf


https://cimg6.ibsrv.net/gimg/pprune....55dace1508.jpg

That video was from Al Jazeera who mdae the documentary "On a Wing and a Prayer" a few years ago. It was shocking then but it even more shocking now, in the light of the issues with the max and the revelations over the Turkish crash.

If it ain't Boeing, then it ain't blowing...

I did some research
 

I watched the documentary, did a quick google search and read the NTSB report on the SWA plane. The documentary was not relevant to the incident plane above which was a very high cycle 300 not an NG. The claims in the second half of the documentary relating the part issues to post accident break up of the fuselage on three hard landings of 737 NG are a stretch.The 707 crash test shown in the documentary was irrelevant. The former FAA expert made claims that the fuselage should not have broken but he provides no basis for that. I don't remember anything mentioned in reports that the fuselage underperformed in the accidents but the operators sure did in each case.
Like AJ's 787 documentary - somewhat over wrought. The people involved filed a whistle blower complaint about the parts sold to the US govt on several models of Boeing's. The lawsuit which was summarily dismissed by the judge. So - draw your own conclusions.

The NTSB report was interesting and as would be expected very thorough. . There was a repair made to a crown panel somewhere between Renton, final assemble and Wichita , where the section was built. This was before Spirit took over the Wichita plant. The repair was badly done. To quote The hole quality in the crown and left side skin panels was not in accordance with Boeing specifications or standard manufacturing practices and showed a lack of attention to detail and extremely poor manufacturing technique.
Not exactly a ringing endorsement of Boeing (unionized ) labor and practices. Brings to mind a poor repair on a pressure bulkhead by Boeing that lead to the loss of a 747.