Boeing 737 3

[thruthefence]

"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.

 

[ESPcomposites]

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

http://www.espcomposites.com

 

[thruthefence]

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.

 

[rb1957]

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 ...

 

[msquared48]

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

 

[blakmax]

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

 

[WKTaylor]

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

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