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Boeing 737
3

Boeing 737

Boeing 737

(OP)
From the Guardian UK, "The US government will order emergency checks of dozens of Boeing 737s after Southwest airlines was forced to ground planes over safety concerns.

Southwest cancelled hundreds of flights after a five-foot tear opened in the fuselage of a plane 20 minutes after taking off from Phoenix on Friday.

The Federal Aviation Administration has now ordered fuselage inspections of older 737-300, -400, and -500 models, involving what could be time-consuming and repetitive electromagnetic checks.

"This action is designed to detect cracking in a specific part of the aircraft that cannot be spotted with visual inspection," FAA administrator Randy Babbitt said.

Boeing will offer its own advice to airlines outlining specific inspection steps."

Dik

RE: Boeing 737

Anyone else have a habit of looking at the date codes on the aircraft as you board?

I'll still fly on them, as Aloha Airlines Flight 243 showed just how much damage a 737 can withstand and still remain airborne.  That was adhesive failure, if I remember correctly.

 

RE: Boeing 737

About 5 years ago, I was flying from Chicago to Buffalo on a 737, got bumped up to 1st class and was enjoying my little perk.  At the last minute this guy just makes onto the plane, obviously ticked-off, mumbling and grumbling to himself.
His seat was next to me, before he sits down, he stops, looks around, then mumbles to himself "piece of s--t airplane".  Takes his seat, and puts his well worn binder down, on the cover its has the Boeing logo.

RE: Boeing 737

When I looked at the failed section, I had two structural questions:

1.  Other than for cost reasons, why were the rivets not staggered to increase the length of the line of any laminar tearing failure, which occurred?

2.  Not sure, but it appeared that the skin panels were not staggered in placement, but started and stopped at each airframe rib.  If so, why?  This significangtly reduces the strength of the fuselage skin diaphragm.    

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Boeing 737

1) the stringer flanges are typically only wide enough for a single rivt row.  particularly for older Boeing designs which used an inverted "top-hat" stringer section, with te frames "floating" on the inner strnger flanges (and shear ties to the fuelage skin).  also rivet pitch is limits the compression strength of the skin, more than 6-8 D you reduce the 30t effective width.

2) i doubt that each frame bay is a separate panel.  longitudinal joints tend to be straight.  They could be off-set, but that'd be loat more complicated to fit together.  Generally panels will have aligned edges longitudinally, their circumferential edges will be off-set.

RE: Boeing 737

Not to be fecetious, but for the rivet spacing I see, and I do understand about the max spacing to provide support for the skin, it seems like a zipper might work about as well.  The end result would be the same in a failure, but it could be quickly repaired.  bigsmile

I guess that the aviation industry is a lot like Pre-Engineered Metal Buildingss, cost and weight driven, and to the limit, unfortunately in my opinion.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Boeing 737

Does anyone know if these lpa splices are adhesively bonded or just installed with sealant? I know that Aloha 243 was manufactured using a room temperature curing film adhesive. That had to be used frozen or it would prematurely set. When exposed to the atmosphere condensation formed on the surfaces and that would inhibit the bond and trap water causing corrosion. They stopped using that material at about LN 290. What do they do now?

Regards
Blakmax

RE: Boeing 737

I don't know if the culture at Boeing had changed for the 737-300 from that of the 737-200. For the earlier airplane, when the rivet holes of metal skin could not line up with the holes in the ribs, the mechanics found a way to stretch and pull on the sheet until the holes lined up, then the rivets were installed under great stress. They did this instead of asking engineering for a solution. In fact, engineering was not even told about this "solution". A lot of us only found out about this manufacturing "solution" years later after Aloha Airlines flt 243.  

RE: Boeing 737

i think that needs some clarification.  

1) Manufacturing have some inherent authority to "adjust" things so they go together.  If they have to exceed their allowance then Liaison disposition the repair with their own authority, or with production support engineering.  of course, i know there is a real world out there and corners get cut.  we're relying on a combination of professionalism and self-interest ... the self-interest comes in

2)  it would be very unusual (= poor?) design to create full size holes in both pieces prior to installing the rivet.  typical would be pilot holes, which give alot more tolerance to misalignment.

RE: Boeing 737

"In fact, engineering was not even told about this "solution". A lot of us only found out about this manufacturing "solution" years later after Aloha Airlines flt 243"

I have read a great deal about the aging aircraft problem, and specifically the Flt 243 incident. I have never read, or (before now) been made aware about a manufacturing defect of this sort leading to the failure. Can you cite a source for this information?

If true, I would think it would be the subject of intense media scrutiny.   

It would also call into question the whole question of "aging aircraft" failing due to cycles & old age, which assumes proper design, & proper manufacture in the first place.

Further, if this is simply "water cooler talk",without substantive evidence, you do a great disservice to the designers AND technicians who build the aircraft, by passing it along as "inside information".

Where may I find documentation on this issue?

RE: Boeing 737

AFAIK Aloha 243 was deterioration of on an epoxied lap joint by the salt air. Didn't know to inspect for it till they had that particular failure.

RE: Boeing 737

Guys... in the absence of any hard "why-it-failed-data"... there are (3) [or possibly more] serious issues at hand. Simplified...

Good/Good for Boeing. The skin failed due to maintenance induced damage [scribe-lines, maintenance impacts, etc] induced the skin damage, but the cabin roof opened/depressurized as anticipated...NOT zipper-failing like the Aloha AL B737-200,  significantly beyond the area of fatigue damage.

Bad/good for Boeing. The skin failed locally in fatigue [thru fasteners] but did not zipper-fail significantly beyond the area of fatigue damage.

Bad/Bad for Boeing. The Skin failed in fatigue and zippered-open far more than predicted by analysis or testing.

Meaning...

Good/good = predictable/stable DADTA and catastropic failure modes/models... except for unpredictable [critical] maintenance issues.

Bad/good = fatigue damage that was NOT anticipated by the DADTA models, but the failure mode was stable/contained.

bad/bad = fatigue damage and failure-modes/models are proven to be grossly unacceptable, bringing into question all other similar Boeing analysis.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

RE: Boeing 737

I'm wondering it it's a design/usage mismatch.

When the 737 first appeared, it was used/ sold/ designed(?) for short flight legs, where it would not usually reach a high altitude.  Other, larger, planes were used on longer legs.  No airplanes were utilized to 100 pct load for 100 pct of the time, either.

Then the world changed...

Now, Southwest uses 737s for _everything_, including long legs at high altitude, and everybody runs with all seats full nearly all of the time, and keeps their airplanes airborne for much more of the day than was the case when the 737 was designed.

I just wonder if the fatigue cycle calcs included the large number of cycles per day that are typical now, and cycles to high altitude also?
 

Mike Halloran
Pembroke Pines, FL, USA

RE: Boeing 737

I think 37's crash & fail because people fly the crap out of them everywhere. A large amount of failures are in them because a large portion of takeoffs are in them.  

RE: Boeing 737

This plane had almost 40000 cycles.  Boeing figured it was good for 60000 before comprehensive inspection.  Figuring was wrong.

RE: Boeing 737

Moon161: AFAIK Aloha 243 was deterioration of on an epoxied lap joint by the salt air.

The salt air may have accelerated the problem, but it was laways going to happen to Aloha 243 or some other of the earlier 737s. To add to my posting a few ahead of yours, I can explain how metal-epoxy bonds work. There are chemical bonds (mainly covalent) formed at the time the adhesive is cured. These bonds form between the metallic oxides and hydroxides on the surface of the metal and the epoxy molecules. These chemical bonds provide the strength for the adhesive to metal bond.

In the case of Aloha 243 and before about ship 290, they used a room temperature curing adhesive film material, and as previously posted, the moisture that condensed on the surface inhibited the formation of those chemical bonds and also led to moisture entrapment which in turn led to corrosion under the lap-splice. A second factor in bond performance is the ongoing integrity of the chemical bonds, because these may under certain cercumstances be susceptible to hydration which leads to disbonding. The mechanism is the presence of water (see TOPOGRAPHIC AND SURFACE CHEMICAL ASPECTS OF THE ADHESION OF
STRUCTURAL EPOXY RESINS TO PHOSPHORUS OXO ACID TREATED
ALUMINUM ADHERENDS by Gary Alan Nitowski) and since the room temeprature curing film adhesive trapped water, the mechanism for bond failure was readily available.

The real error was the selection of a room temperature curing adhesive system.  

RE: Boeing 737

So, are you saying that the glue is the primary structural connector and not the rivets?  If so, then, are the rivets only there to provide a uniform compression force along the section to obtain a good bond?  

If so, where is the extra structural capacity for overload, the safety factor, the structural duplication against failure?  It seems to me like a failure just waiting to happen.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Boeing 737

Scares the hell out of me to depend on glue.  But then, if I designed one, it would be too heavy to get off the ground.

RE: Boeing 737

Me too, Hokie.  Me too.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Boeing 737

i don't know that you can blame all RT resin systems .... Fokker have used RT resins for decades, without problems.  in my experience, it it the process compliance that is the root of the problems.  Boeing now uses a much better (reliable) systeem (PAA) and much tighter process controls.

the best thing that can be said about SW is that 1st no-one died, and 2nd this is probably the most highly stressed (certainly most highly loaded) part of the fuselage.  Interestingly the failure happened without max cabin pressure.

i'd add to the previous posts (noting that i'm not particularly a Boeing fan) that we're looking at an airplane designed 50 years ago and it has stood up pretty well to that experience.  it was designed before damage tolerance, and in the early days of fatigue; fail safe was in it's infancy.  

the Aloha incident was a combination of errors (as all incidents are) ... the basic design was possibly suspect, the maintenance was not complete (not through negligence), the certification was questionable.  this produced the aging aircraft re-cert program, highlighting the (possibly obvious) interconnection between OEM, maintainer, and certiication.  remember too that this design is early in the development of mandatory structural inspections, and operators had to understand the importance of these.

In-service usage would be closely monitored by Boeing; yes, each operator is different to the certification spectrum, but their operations are assessed (by Boeing or by themselves) to ensure that the correct assessment of fatigue effects (again, fall-out from Aloha).

RE: Boeing 737

Msquared48

In a properly formed adhesive bond, the fasteners will carry negligible shear loads and the bond will carry almost everything. This is because unlike the populous theory that adhesive bonds spread the load over the entire bond, in reality the shear stresses peak at the ends of the joint and decay to zero within a relatively short distance along the bond. Most of the load is transferred at the ends of the joint. The closest a fastener can be installed to the edge of the joint is determined by tear-out considerations and is typically 1.5 times the diameter of the fastener. Hence, all of the load will be transferred by the adhesive before the fastener even experiences any load.

The fasteners attach the joint to the frame and carry out of plane loads.

As for the fears expressed in relation to adhesive bonding, it is by far the best method for joining such structures, provided the processing is correctly validated and implemented, which in the case of Aloha 243 it was not. Given the thickness of the skins on the 737 if they were effectively and correctly designed and bonded, the adhesive itself should never fail. It is possible to design bonded joints such that the metal will always break, not the adhesive.

Adhesive bonds also have the advantage of not introducing the 300% increase in stress caused by fasteners.

With regard to the Fokker use of RT adhesives, they never attempted to use a pre-mixed film adhesive which had to be used frozen. That was the error in the design of the early 737 lap joints.  

RE: Boeing 737

To all you target builders out there (msquared & hokie in particular), for an example of what happens in a pressurized airliner when manufacturing staff persuade engineering not to use adhesive, take a look at the comet story.

Folks coming from other sectors have trouble in aerospace getting their heads around the mass issue.  My first boss's background was in naval dockyards not aerospace, when he got given responsibility for some airborne kit he had to constantly remind himself about mass being the enemy.

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RE: Boeing 737

"manufacturing staff persuade engineering not to use adhesive, take a look at the comet story."

I have read that the marketing people overruled engineering (who wanted "rounded" window openings) in favor of the Comet's squarish windows, because they "didn't want the windows to look like portholes on ship."

Where were we with bonding technology in the early 50's anyway?

RE: Boeing 737

From my ever worsening memory...

They had some proprietary bonding technology or something.  They built up sample fuselage sections using this bonding around the windows, I think in conjunction with rivets but don't recall for sure, and subjected them to fatigue testing of pressurization cycles.

Apparently the bonded design was a pig to build or something and manufacturing wanted to move to riveted only design.  This was approved without repeating the fatigue testing.

To make it worse I believe holes were punched not drilled/reamed and of course many windows and fuselage cut outs had sharp corners.

DeHaviland were probably amongst the world leaders in aerospace adhesives, look how much they used it on their wartime aircraft.

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What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Boeing 737

a joint can be properly designed using adhesive, adhesive and rivets, or rivets alone.

they did do a fatigue test on the comet, quite ground breaking (no pun intended) for the time.  unfortunately they used the static test specimen (since it was still intact) and that (as we know now) invalidates the results.

RE: Boeing 737

rb1957 said"a joint can be properly designed using adhesive, adhesive and rivets, or rivets alone".

This is true, but the strength of that joint follows exactly the sequence you stated. One military aircraft with a composite to titanium multi-step joint was evaluated for bonding, bonding and fasteners and fasteners only. The results from memory were approx. 35,200 lb/in for bonding, and 28,500 lb/in for bolting. For bonding and bolting the strength was 34500 lb/in and the bolts carried just 400 lb of load. So by adding bolts, the strength dropped and the bolts carried next to no load.

There is no question that properly designed and fabricated adhesive bonded joints are stronger, lighter and more fatigue resistant than either bolts alone or bonding and bolting. The only reason we do not see more adhesively bonded joints is the "Grandma's cup syndrome"; I glued Grandma's cup with that glue stuff and it broke again.

The fundamental reason we see bond failures on aircraft is that the FARs require demonstration of static strength and fatigue resistance, and most bond failures can not be prevented by static or fatigue testing. The are due to chemical, time dependent dergadation of the bond interface, usually by hydratrion of metal oxides. Fir the oxides to hydrate, the chemical bonds formed at the interface dissociate, leading to interfacial failure of the bond. There are tests to demonstrate resistance to hydration for bonded joints and if these were mandated, we would not see bond failures in service and we would achieve the weight savings and sign ificant fatigue improvement that can be achieved by bonded structures.

I'd be happy to discuss what a waste of time NDI and damage tolerance are for bonded structures, but that may be getting too far from the topic.

Regards

Blakmax

 

RE: Boeing 737

(OP)
I don't have a real problem with adhesives... I'd used them for plywood gussetted trusses 40 years ago because I had more confidence in the glue than I did in nails...

Dik

RE: Boeing 737

the order of joint designs was not intended to show an order of preference or acceptability.  the point made about adhesive being process dependent and possibly degrading over time this IMHO enough of a hit to question them entirely ... yeah, i know there's a baby in the bathwater but ...

i've learnt enough to be very careful of adhesive joints.

RE: Boeing 737

"I'd be happy to discuss what a waste of time NDI and damage tolerance are for bonded structures"

What can be done, in an inspection environment, to insure the continued airworthiness of bonded structures?


Maybe we need a new thread?

RE: Boeing 737

do it right the first time ... a correctly produced adhesive joint should outlast the aluminium around it.

the problem is incorrectly produced adhesive which can degrade very quickly.

I guess what we haven't found is a method to detect an incorrectly produced adhesive joint

RE: Boeing 737

Kenat et al:  

I am well aware about the mass issue as s Hokie.  I too am aware of the Comet.  However, I am also well aware of the result of any failure in this current instance.

In structural building engineering, one of the basic tenets is to buy time for the occupants to survive an event of an acceptable risk.  The problem I have with the glue, is that the failures are sudden and the weaknesses generally not detectable until the failure.  To date, we have been lucky.

To me, the current technique, although apparently the best we have, is just not good enough.  There must be a better way to get a more reliable result.  Complacency with the current methods and materials is not the answer.  Finding other options is.  

It is true that many materials we have in buildings use glue, but we are trained not to rely on any contribution, except that which has been adeqauately tested, as in plywood, glulam beams, paralams, etc.  Occasionally, I also use glue in other circumstances, but never totally rely on it in a connection.  Every coffee cup I have ever mended with epoxy has eventually failed.  I just don't trust glue.

This is not a rant on aeronauticals or the aircraft industry in general.  I just think we can do better, and should as engineers, that's all.  No offense intended guys.   

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Boeing 737

"Every coffee cup I have ever mended with epoxy has eventually failed.  I just don't trust glue."

How many coffee cups have you fixed with rivets? ;)

RE: Boeing 737

for a coffee cup, failure provides two acceptable futures ...
1) retirement, or
2) accepting reduced functionality (loss of a handle).

the 3rd option (repair) is fraught with possible in-service sudden failure resulting in unacceptable consequences.

RE: Boeing 737

all i said was ...

RE: Boeing 737

Not to muddy this any further, but bonded repairs are an interesting case as well.

I believe the current strategy (per FAA) for bonded repairs is that structure must still be capable to limit load in the event of a failed bond. Ultimately, we just can't trust them yet. As said, they are great when done correctly, but very poor if not done correctly. In the real world, they are not always done correctly and that possibility must be addressed.

Brian
www.espcomposites.com

RE: Boeing 737

Documented??? People want "documented" information? The information about the skin panels being stretched is from the engineers whom I worked with on the early -200 line. Boeing will NEVER have this information "documented". So, I guess go beleive only what is "documented" if that determines what you believe.  

RE: Boeing 737

My best structures prop told similar stories about the Harriers he saw being built at British Waste of Space in the 80's.  Some guy under the A/C, on his back using his feet and arms to push the panel into place or something.

Hammer to shape, File to fit, Paint to match right?

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RE: Boeing 737

"Documented??? People want "documented" information? "

Maybe I missed it, but in the NTSB reports, and the volumes of scholarly dissection of the accident I don't remember seeing anything about this.I would think the forensic gnomes would have uncovered SOME evidence of "skin stretching" on the indecent aircraft, or the hundreds of other s/n specific aircraft that were inspected after the fact.

And I would think, that at least one of the "engineers whom I worked with on the early -200 line." would have the ethics (and the balls) to speak up on this subject.



 

RE: Boeing 737

How exactly would the mechanic apply a force to achieve a "great stress" in the rivets? Wasn't this a fuselage issue, so did you mean a stringer or a frame, and not a rib? And if you were bending or stretching those structures, wouldn't there be associated cracking in those members as well..or at least some indication of unexpected preloads?  

Brian
www.espcomposites.com

RE: Boeing 737

a correction; while it was "indecent" of the 737 to behave in such an unseemly manner, My intent was to type "incident".

thruthefence regrets any confusion.  

RE: Boeing 737

from Flight ...
Speaking at the MRO Americas conference in Miami, FAA administrator Randy Babbitt said: "People have leaped to the conclusion that it was fatigue. The airplane didn't have that many cycles on it so we're looking at other things. The manufacturing techniques. Boeing is very interested too. This is not good for anybody's business."

either somebody spoke up, somebody noticed something with the a/c, or maybe somebody is reading this ...

 

RE: Boeing 737

blakmax:

You stated earlier that "In a properly formed adhesive bond, the fasteners will carry negligible shear loads and the bond will carry almost everything."

From the recent press clips here, the initial assessment is that the rivet holes were improperly sized during the original assembly, allowing for working of the rivet connections and fatigue to develop over time.  If the glue takes all the stress, then why did the rivet failure play any part here in the failure?

Perhaps I do not understand the detail of the connections.   

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Boeing 737

Mike

It would depend on if the bonding material was a structural adhesive or just a sealant. If they use sealant and rely on fasteners to transfer the load, then fatigue may occur because sealants are usually compliant and do not transfer much load in shear.

It would also depend upon what loads are transferred from the frames into the skins at the splice, especially if the fasteners as reported were poorly fitted.

If they did use a structural adhesive, then there may have been a processing issue for the bond.

To clarify, any longitudinal or hoop loads in the skin before the joint should be transferred by the bond. Any additional load introduced by the fasteners from the frames will result in loads in the fasteners (naturally). These loads will be transferred by the bond in a short distance from that fastener.

Now what surprises me is that if these were structural bonds and the miss-fit was sufficient to cause the additional bearing stresses to initiate fatigue cracks, the bond to the other skin should have provided significant crack opening restraint such that any crack growth would be slow. So (1) these cracks had initiated early in the aircraft life, or (2) the bond was deficient, or (3) the bond is not formed using structural adhesives.  

Regards

Blakmax
 

RE: Boeing 737

Boeing Factory Probed in Rupture of Southwest Jet
APRIL 25, 2011
By ANDY PASZTOR And PETER SANDERS

http://online.wsj.com/article/SB10001424052748704123204576283370460150808.html?mod=dist_smartbrief#   

Investigators suspect that a manufacturing lapse at a Boeing Co. factory 15 years ago is why the fuselage of a Southwest Airlines Co. jetliner ruptured in midair this month, according to government and industry officials.

It is too early to draw definitive conclusions, the officials said, and further testing and data analysis could bring other issues to the forefront. But the federal probe increasingly is focused on some type of assembly-line lapse—a rare occurrence in modern aircraft production— that would explain an incident that stunned the airline industry and worried travelers.

The Boeing 737-300, with 122 people aboard, had a five-foot gash rip open in the upper part of its cabin and suffered a rapid decompression while cruising at about 34,000 feet on April 1. No one was seriously hurt and the twin-engine jet made an emergency landing at a military base in Arizona.

The incident prompted Southwest to temporarily ground and immediately inspect 79 of its oldest Boeing 737s and sparked a round of swift inspections of about 100 more aging 737s at other airlines world-wide. Hundreds of additional jets are slated to undergo the same checks in coming years as they rack up flights.

In addition to the Southwest plane that ruptured, five of the airline's other aging 737s were found with fuselage cracks requiring repairs.

The 737 fuselages are built at a factory in Wichita, Kan., which in 1996 was wholly owned by Boeing.

Boeing said no similar problems have been discovered at other airlines. "No conclusions have been reached about the root cause of the inspection findings" or how they may relate to the April 1 event, and "any attempt to draw conclusions on either would be premature and speculative," the Chicago-based company said.

Production-line snafus happen occasionally to all aircraft makers, despite strict standards, substantial quality-assurance teams and constant government oversight. Starting in the late 1990s, Boeing suffered its share of 737 problems, from loose nuts on the tails of some planes to improperly wired engine-vibration and fire-warning systems. But most of those problems were identified and fixed relatively quickly.

This time, investigators led by the National Transportation Safety Board are trying to unravel the potential impact of riveting techniques and certain sealants going back to around 1996, according to the officials. They said investigators also are looking into factory tooling used to hold plane parts during assembly. Possible production problems were reported Saturday by ABC news.

A big reason behind the manufacturing-related focus, according to government and industry officials, is that a number of the Southwest planes with fuselage cracks were built around the same time. The officials said it is too early to know whether the suspect Southwest jets illustrate a quality-control problem involving specific workers and a relatively short span of time, or whether they are the result of broader production issues.

Jets flown by other carriers, even some with more flights that the ruptured Southwest plane, haven't shown signs of structural weakness or fatigue.

The Southwest plane had logged about 39,000 takeoffs and landings, substantially fewer than the point at which Boeing experts anticipated it could face serious metal fatigue. The stresses planes undergo each time their cabins pressurize and depressurize during a trip are major factors in creating cracks and possibly causing metal fatigue.

"Inspections have been completed world-wide on approximately 75% of the 190 airplanes affected" by mandatory inspection rules, and only the handful of Southwest planes have "shown small subsurface cracks," Boeing said. Those portions of their aluminum skins are being examined at Boeing facilities.

A spokeswoman for Dallas-based Southwest declined to comment on the investigation.

Federal Aviation Administration chief Randy Babbitt said this month that his agency and Boeing were looking into "manufacturing techniques," among other things. Mr. Babbitt said FAA experts were examining existing inspection rules for aging aircraft and seeking to determine, "Are we looking at the right things?"

Over the decades, the FAA and the industry have developed a set of inspection procedures to identify and repair fuselage cracks on aging jets before they can lead to major safety hazards. The Southwest incident this month surprised regulators and airlines because Boeing had reassured them the planes didn't need to undergo detailed structural inspections on that part of its fuselage for at least several more years.

The planes targeted for inspection were 737 models manufactured between 1993 and 2000. Boeing executives have said that because of a fuselage design change, current 737 models are unaffected by the problem.

The newer version of the 737—dubbed "737 Next Generation"—made its maiden flight in February 1997, and the first one was delivered to Southwest Airlines in 1998. Since then, more than 3,500 have been delivered, and there are more than 2,000 on order from airlines world-wide.

The 737NG aircraft features a modified wing, 16 feet longer than the models it replaced, and holds 30% more fuel. Combined with new, more fuel-efficient engines, the NG family can fly more than 900 miles farther than its predecessors.

The aging-aircraft inspection mandates primarily apply to the earlier 737 models, many of which have been retired by large Western airlines and are now flying in less-developed regions.
 

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

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