How did the FAA and Boeing identify the 175 737 Classics?

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How did the FAA and Boeing identify the 175 737 Classics? By

Jon Ostrower  on April 5, 2011 12:05 AM | Permalink | Comments (12) | TrackBacks (0) | With the coming of Tuesday's Federal Aviation Administration emergency airworthiness directive, there are still a few key questions left unanswered by the identification of the 175 737-300, -400s and -500s worldwide that will require intensive Eddy-current inspections of their fuselage lap-joints. 
For quick catch up, a 737-300 made an emergency landing in Yuma, Arizona on April 1 after developing 5ft hole in the upper fuselage, which has since been traced to a pre-existing structural fatigue.
Only about 80 aircraft in the US are subject to the inspections, and almost all are the Southwest Airlines 737-300s that will all have completed inspection by late Tuesday. 
So what of the other approximately 95 Classics around the world?
Boeing says the group of 175 was narrowed down by two criteria:The airframes in question had to have 30,000 or more operational cycles. 
Southwest says the airframes in question were "designed differently in the manufacturing process". Boeing confirms there are differences in the lap-joint design, and the specific configuration, says the airframer, was phased out as part of a blockpoint change during the 737 Classic's production run. The number of aircraft with this design is significantly higher than the aircraft identified by the FAA and Boeing, though only 175 meet the criteria when paired with 30,000 or more cycles.
The specifics of that design configuration are yet undisclosed, though just how much information is shared publicly is up to Boeing and the FAA. 
The natural question that will come along with these available facts is what prompted the different lap-joint design in the first place? And what's being done to ensure the aircraft with this older design along and fewer than 30,000 cycles are properly cared for just as the higher-cycle aircraft? Categories: Boeing Tags: 737, Boeing, FAA, Southwest Airlines 0 TrackBacks

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12 Comments By alloycowboy
on April 5, 2011 12:17 AM | Reply

Hey Jon,

Do you think this will accelerate the 737 replacement program espically if Southwest is forced to prematurely invest in new air planes.

By database design software
on April 5, 2011 1:11 AM | Reply

Qantas airlines and Southwest airlines both have the safest track record in aviation history. Both companies have NEVER had a plane fall out of the sky. Most United airline planes are extremely old planes. One of the reasons why southwest can operate at a lower cost, is because they pay a fixed price for their fuel.

By JetAviator7
on April 5, 2011 8:03 AM | Reply

I never realized that buyers could specify details down to that level of construction.

I assume it had something to do with costs because it seems everything today is driven by costs.

Whatever happened to the idea of quality over price?

By Rick Denton
on April 5, 2011 8:39 AM | Reply

@JetAviator7: Where do you read that the different lap joint design was specified by a customer rather than an engineering change initiated by Boeing? I think your assumption regarding cost is baseless and doesn't apply.

By RobH
on April 5, 2011 9:36 AM | Reply

Expanding on Mr. Cowboy's post, I'm very interested to see how this will affect the internal debate on whether or not to use CFRP on the 737RS.

By Scentsy
on April 5, 2011 11:58 AM | Reply

Nothing lasts forever. I remember Delta's last 737-300's(which actually began life as Western Air Lines,RIP!)and heading out to preflight in the morning only to find the acft destination was KVCV w/no pax. Great airplane but she needs TLC!

By Tom
on April 5, 2011 1:00 PM | Reply

http://english.aljazeera.net/programmes/peopleandpower/2010/12/20101214104637901849.html#

By Zippy
on April 5, 2011 1:07 PM | Reply

I seem to recall that there was a lap joint maintenance procedure for some 737s where they'd seal the lap joints, then use a sharp edge, like a box cutter, to remove excess sealing material. This was scoring the body panels, leading to a location where fatigue cracking occurred. Could that be related to this problem?

By Zippy
on April 5, 2011 1:13 PM | Reply

There's a pretty good discussion of lap joint scoring here.

http://www.b737.org.uk/fuselage.htm

By Bob
on April 5, 2011 1:54 PM | Reply

Reports are out that Paul Richter, a Boeing Chief Project Engineer, said in a conference call today that 570 older 737s are at risk for cracks. That's a far cry from the 175 that the FAA wants inspected.

Stress cracks were anticipated, but not before the jets had performed at least 50,000 flights. Now Boeing says safety checks for the older 737s, delivered between 1993 and 2000 should be carried out after 30,000 flights, and then again every 500 flights. Each inspection takes about eight hours, on average, Richter said on the conference call.

By Jetmech
on April 5, 2011 4:32 PM | Reply

John, can you look into Southwest's outsourcing of maintenance to El Salvador?

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

I'm wondering if service ceiling should be lowered on those older high cycle aircraft? Many cycles of high altitude flying probably contributed to earlier failure.

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