Southwest FLT 812 Decompression and diversion
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rwedareyet
I agree with you. It is odd that United and USAIR didn't have the same problem. I do know that USAIR had the best ageing aircraft program in the country.
I agree with you. It is odd that United and USAIR didn't have the same problem. I do know that USAIR had the best ageing aircraft program in the country.
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The reason that UA didn't have any trouble is that they have none on the property as of 2009, at least according to Wikipedia?
United Airlines - Wikipedia, the free encyclopedia
United Airlines - Wikipedia, the free encyclopedia
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Southwest with about 80 aircraft and Alaska with about 2 where the only two airlines in the USA that needed to have their aircraft inspected and were grounded till inspected....
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seven......
United Airlines Fleet | Airfleets aviation
I agree with you. It is odd that United and USAIR didn't have the same problem. I do know that USAIR had the best ageing aircraft program in the country.
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A Long history of fuselage cracks
Nothing new about these fuselage cracks, but rather that they aren’t being caught in time.
A quick and dirty search of the Service Difficulty reports for users like Continental, United, US Air, American and Southwest shows over 260 SDRs of fuselage cracks from 2000 through this year.
Over 14 ADs have been issued since 2002 including; 2002-07-08, 2002-07-10, 2002-07-11, 2003-08-15, 2003-23-03, 2004-18-06, 2004-23-10, 2005-13-27, 2005-13-30, 2007-26-04, 2008-12-04, 2008-19-03, 2009-21-01 and 2010-01-09 affecting every model of the 737s from the 200s to the 900s (2008-12-04).
Worst yet, is the appearance that the chem.- milled sheet step-cracking problem has carried forward to the 757s with AD-2011-01-15.
Just plug in the AD numbers above into this AD search query for full details >
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/MainFrame?OpenFrameSet
A quick and dirty search of the Service Difficulty reports for users like Continental, United, US Air, American and Southwest shows over 260 SDRs of fuselage cracks from 2000 through this year.
Over 14 ADs have been issued since 2002 including; 2002-07-08, 2002-07-10, 2002-07-11, 2003-08-15, 2003-23-03, 2004-18-06, 2004-23-10, 2005-13-27, 2005-13-30, 2007-26-04, 2008-12-04, 2008-19-03, 2009-21-01 and 2010-01-09 affecting every model of the 737s from the 200s to the 900s (2008-12-04).
Worst yet, is the appearance that the chem.- milled sheet step-cracking problem has carried forward to the 757s with AD-2011-01-15.
Just plug in the AD numbers above into this AD search query for full details >
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/MainFrame?OpenFrameSet
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News reporting here in Oz that the problem has been traced to a manufacturing defect. Apparently the section rivets were incorrectly fitted - the drilled holes were too large, leading to movement in the joint.
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Doesn't make sense
Regarding the above post Permlink #198)- “News reporting here in Oz that the problem has been traced to a manufacturing defect. Apparently the section rivets were incorrectly fitted - the drilled holes were too large, leading to movement in the joint.”
This doesn’t make sense. Here is why.
Rivets or Hy-Locs ?
If the fasteners were rivets – then the rivets would assume the precise size of the holes drilled as they swell. We are talking in a few thousands of an inch and assuming they didn’t abandon all common sense (if it wiggles, something is wrong).
More likely - they were Hy-Locs which come in graduated oversizes to accommodate hole sizes including those that have been re-worked or enlarged in the removal of any earlier fasteners (rivets or Hy-Locs). For each specific oversized Hy-Loc, there is a specific oversized drill. Hy-Locs come in two components; the Hy-Loc itself, and a threaded collar incorporating a hex/nut portion to allow the collar to be driven by a wrench, a socket, or more commonly, an air powered driven socket wrench. Once proper tension is achieved, the ‘nut’ portion snaps away and leaves a small collar.
Hy-Locs won’t install in an oversized hole.
More importantly, there is a built-in feature to prevent wrong sizing with every Hy-Loc installation. The ‘nut’ can only be driven if the Hy-Loc does not rotate in the hole.
You can not drive the nut to the required tension permitting the ‘nut’ portion to snap away with a spinning Hy-Loc !
It is this interference fit – the ‘grip’ – that assures the hole sizing, and the Hy-Loc size selected are proper.
Drilling out fasteners changes the original hole sizes
Lastly, you can’t determine the original hole size after having drilled out a rivet. When it was driven, it may have swelled and expanded that hole, or more likely, by drilling it out, some hole material was also taken out as well and thus you have a ‘double hole’, one that is enlarged or ‘out-of-round’.
So, in sum, wrong sized holes at the manufacturing level where thousands of fasteners are installed a day seems highly improbable where not only are the installers involved, but also the Q.C. guys. It doesn’t make sense. Boeing has had a number of controversies but the very basics of fastening shouldn’t be one of them.
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This doesn’t make sense. Here is why.
Rivets or Hy-Locs ?
If the fasteners were rivets – then the rivets would assume the precise size of the holes drilled as they swell. We are talking in a few thousands of an inch and assuming they didn’t abandon all common sense (if it wiggles, something is wrong).
More likely - they were Hy-Locs which come in graduated oversizes to accommodate hole sizes including those that have been re-worked or enlarged in the removal of any earlier fasteners (rivets or Hy-Locs). For each specific oversized Hy-Loc, there is a specific oversized drill. Hy-Locs come in two components; the Hy-Loc itself, and a threaded collar incorporating a hex/nut portion to allow the collar to be driven by a wrench, a socket, or more commonly, an air powered driven socket wrench. Once proper tension is achieved, the ‘nut’ portion snaps away and leaves a small collar.
Hy-Locs won’t install in an oversized hole.
More importantly, there is a built-in feature to prevent wrong sizing with every Hy-Loc installation. The ‘nut’ can only be driven if the Hy-Loc does not rotate in the hole.
You can not drive the nut to the required tension permitting the ‘nut’ portion to snap away with a spinning Hy-Loc !
It is this interference fit – the ‘grip’ – that assures the hole sizing, and the Hy-Loc size selected are proper.
Drilling out fasteners changes the original hole sizes
Lastly, you can’t determine the original hole size after having drilled out a rivet. When it was driven, it may have swelled and expanded that hole, or more likely, by drilling it out, some hole material was also taken out as well and thus you have a ‘double hole’, one that is enlarged or ‘out-of-round’.
So, in sum, wrong sized holes at the manufacturing level where thousands of fasteners are installed a day seems highly improbable where not only are the installers involved, but also the Q.C. guys. It doesn’t make sense. Boeing has had a number of controversies but the very basics of fastening shouldn’t be one of them.
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Doesn't make sense
So, in sum, wrong sized holes at the manufacturing level where thousands of fasteners are installed a day seems highly improbable where not only are the installers involved, but also the Q.C. guys. It doesn’t make sense. Boeing has had a number of controversies but the very basics of fastening shouldn’t be one of them
VFD
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April 25th UPDATE from NTSB
NTSB Press Release
"... NTSB Materials Laboratory, microscope examination of the fracture faces of the ruptured skin revealed fatigue cracks emanating from at least 42 of the 58 rivet holes connected by the fracture. Electrical conductivity measurements, hardness tests, and X-ray energy dispersive spectroscopy elemental analysis of the skin in the area of the fracture revealed that the aluminum skin material was consistent with the specified material. The skin was the specified thickness.
"Non-destructive eddy current inspections conducted around intact rivets on the removed skin section forward of the rupture revealed crack indications at nine rivet holes in the lower rivet row of the lap joint. To assess the condition of the intact rivets and the skin rivet holes, X-ray inspections were performed on the skin located forward of the rupture location. This inspection revealed gaps between the shank portions of several rivets and the corresponding rivet holes for many rivets associated with S-4L. Upon removing selected rivets, the holes in the upper and lower skin were found to be slightly offset relative to each other and many of the holes on the lower skin were out of round.
"In this ongoing investigation, the NTSB Materials Laboratory work is actively conducting additional inspections and examinations in the following areas:
"... NTSB Materials Laboratory, microscope examination of the fracture faces of the ruptured skin revealed fatigue cracks emanating from at least 42 of the 58 rivet holes connected by the fracture. Electrical conductivity measurements, hardness tests, and X-ray energy dispersive spectroscopy elemental analysis of the skin in the area of the fracture revealed that the aluminum skin material was consistent with the specified material. The skin was the specified thickness.
"Non-destructive eddy current inspections conducted around intact rivets on the removed skin section forward of the rupture revealed crack indications at nine rivet holes in the lower rivet row of the lap joint. To assess the condition of the intact rivets and the skin rivet holes, X-ray inspections were performed on the skin located forward of the rupture location. This inspection revealed gaps between the shank portions of several rivets and the corresponding rivet holes for many rivets associated with S-4L. Upon removing selected rivets, the holes in the upper and lower skin were found to be slightly offset relative to each other and many of the holes on the lower skin were out of round.
"In this ongoing investigation, the NTSB Materials Laboratory work is actively conducting additional inspections and examinations in the following areas:
- Removal of rivets and examination of rivet hole dimensions, rivet dimensions, and rivet hole alignment between upper and lower skins.
- Detailed fractographic analysis of the skin fractures emanating from the rivet holes using optical and scanning electron microscopes.
- Fatigue striation analysis using a scanning electron microscope of specific skin fractures to determine the rate of crack propagation.
- Additional portions of the lap joints from the accident aircraft...."
We seem to have a manufacturing or repair defect here.
Off topic, as for DC9 vs. B737, there were different design philosophies at work. Douglas was more elegant than Boeing, or thought they were, as anyone who has examined the pilots opening windows on both aircraft will know.
However Boeing didn't design that elegant tracery of linkages for the DC10 cargo door either.
My experience of dealing with Douglas was always: "Fukc you! What would you know? You are just an airline engineer! We built the DC3!" Boeing actually had a certain humility in dealing with its customers, at least on an engineering level.
Off topic, as for DC9 vs. B737, there were different design philosophies at work. Douglas was more elegant than Boeing, or thought they were, as anyone who has examined the pilots opening windows on both aircraft will know.
However Boeing didn't design that elegant tracery of linkages for the DC10 cargo door either.
My experience of dealing with Douglas was always: "Fukc you! What would you know? You are just an airline engineer! We built the DC3!" Boeing actually had a certain humility in dealing with its customers, at least on an engineering level.
This isn't a customer relations problem.
From my read so far
Fatigue outside of typical reliable lifing expectations
something wrong with the rivet holes
Repair-rework or something else at play here (my light switch on-off theory)
Population suspect associated with a manufacturing time frame rather than basic design philosophy
Happy to be corrected if I misread something.
From my read so far
Fatigue outside of typical reliable lifing expectations
something wrong with the rivet holes
Repair-rework or something else at play here (my light switch on-off theory)
Population suspect associated with a manufacturing time frame rather than basic design philosophy
Happy to be corrected if I misread something.
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Nothing New in Aviation.
Will the NTSB report of the first NGs to suffer this problem take into account the reported defective structural parts supplied to and fitted by Boeing viz. the chord sections and the "bear-straps", which needed a hammer and/or some extra hand-drilled holes out of tolerance, in order to make them fit on the company's assembly line????
Yet again take a look at " A H F DUCOMMUN " in your search engine and see how the sacked whistleblowers are faring. Then thank the lord that we've got such strict oversight of our major aircraft manufacturers......
Sorry, I made that last part up, only joking!
Yet again take a look at " A H F DUCOMMUN " in your search engine and see how the sacked whistleblowers are faring. Then thank the lord that we've got such strict oversight of our major aircraft manufacturers......
Sorry, I made that last part up, only joking!
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Seems Like Old Times
Some Briefs From the Federal Register and ADs. See source Links for full texts.
2002. Inadequate Level Of Safety - lap Joints.
AD- 2002-07-08. 737-200, -200C, -300, -400, and -500 series airplanes having line numbers 292 through 2565 inclusive …… that currently requires repetitive inspections to find cracking of the lower skin at the lower row of fasteners in the lap joints of the fuselage …also requires modification of the fuselage lap joints at certain locations,… . This amendment is prompted by the FAA's determination that, in light of additional crack findings, certain modifications of the fuselage lap joints do not provide an adequate level of safety. Compliance; before the accumulation of 50,000 total flight cycles or within 2,250 flight cycles after the effective date of this AD, whichever comes later. Locations; lower skin at the lower row of fasteners in the lap joints of the fuselage, - stringers 4R and 10R
Source; http://www.airweb.faa.gov/Regulatory...ILE/020708.pdf
2005. Fuselage Structure Tests Failures at 21,000 cycles.
AD- 2005-13-27. 737-300, -400, and -500 series airplanes. …. repetitive inspections for cracking of the crown area of the fuselage skin, ….. prompted by a Model 737 fuselage structure test and fatigue analysis that indicate fuselage skin cracking could occur between 21,000 and 42,000 total flight cycles.. . Within 4,500 cycles. Effective August 1, 2005.
Source; http://www.airweb.faa.gov/Regulatory...2005-13-27.pdf
2006. 757s. Countersinks Too Deep.
2006-20-11. 757-200, -200PF, and -200CBs. ….requires doing initial and repetitive detailed or high frequency eddy current inspections for cracks around the rivets at the upper fastener row of the skin lap splice of the fuselage, and repairing any crack found. This AD results from a report indicating that certain rivets were incorrectly installed in some areas of the skin lap splices during production because they were drilled with a countersink that was too deep. Boeing states that the production rivets are commonly referred to as ''Briles'' rivets, and are manufactured with a 120-degree, modified shear head. Effective 11/8/2006.
Source; http://www.airweb.faa.gov/Regulatory...2006-20-11.pdf
2008. Missing Or Loose Fasteners or Milled Steps.
AD- 2008-12-04. 737- 600, -700, -700C, -800, and -900 series airplanes. ….requires various repetitive inspections to detect cracks along the chemically milled steps of the fuselage skin or missing or loose fasteners in the area of the preventative modification or repairs, …. This AD results from a fatigue test that revealed numerous cracks in the upper skin panel at the chemically milled step above the lap joint. Compliance per the Service Bulletin. Within 36 months. Effective July 16, 2008.
Source; http://www.airweb.faa.gov/Regulatory...2008-12-04.pdf
2011. 100 ADs - Widespread Fatigue Damage .
“Since 1988, the FAA has issued approximately 100 airworthiness directives to address WFD
Widespread Fatigue Damage in airplanes. Approximately 25 percent of these airworthiness directives were too urgent to allow the public an opportunity to comment in advance. These airworthiness directives required inspections, and the FAA later superseded the majority of them to expand the inspections or require modifications because inspections were not enough to preclude WFD. Effective January 14, 2011.” Source; Federal Register; http://www.regulations.gov/#!documentDetail;D=FAA-2006-24281-0088.
2002. Inadequate Level Of Safety - lap Joints.
AD- 2002-07-08. 737-200, -200C, -300, -400, and -500 series airplanes having line numbers 292 through 2565 inclusive …… that currently requires repetitive inspections to find cracking of the lower skin at the lower row of fasteners in the lap joints of the fuselage …also requires modification of the fuselage lap joints at certain locations,… . This amendment is prompted by the FAA's determination that, in light of additional crack findings, certain modifications of the fuselage lap joints do not provide an adequate level of safety. Compliance; before the accumulation of 50,000 total flight cycles or within 2,250 flight cycles after the effective date of this AD, whichever comes later. Locations; lower skin at the lower row of fasteners in the lap joints of the fuselage, - stringers 4R and 10R
Source; http://www.airweb.faa.gov/Regulatory...ILE/020708.pdf
2005. Fuselage Structure Tests Failures at 21,000 cycles.
AD- 2005-13-27. 737-300, -400, and -500 series airplanes. …. repetitive inspections for cracking of the crown area of the fuselage skin, ….. prompted by a Model 737 fuselage structure test and fatigue analysis that indicate fuselage skin cracking could occur between 21,000 and 42,000 total flight cycles.. . Within 4,500 cycles. Effective August 1, 2005.
Source; http://www.airweb.faa.gov/Regulatory...2005-13-27.pdf
2006. 757s. Countersinks Too Deep.
2006-20-11. 757-200, -200PF, and -200CBs. ….requires doing initial and repetitive detailed or high frequency eddy current inspections for cracks around the rivets at the upper fastener row of the skin lap splice of the fuselage, and repairing any crack found. This AD results from a report indicating that certain rivets were incorrectly installed in some areas of the skin lap splices during production because they were drilled with a countersink that was too deep. Boeing states that the production rivets are commonly referred to as ''Briles'' rivets, and are manufactured with a 120-degree, modified shear head. Effective 11/8/2006.
Source; http://www.airweb.faa.gov/Regulatory...2006-20-11.pdf
2008. Missing Or Loose Fasteners or Milled Steps.
AD- 2008-12-04. 737- 600, -700, -700C, -800, and -900 series airplanes. ….requires various repetitive inspections to detect cracks along the chemically milled steps of the fuselage skin or missing or loose fasteners in the area of the preventative modification or repairs, …. This AD results from a fatigue test that revealed numerous cracks in the upper skin panel at the chemically milled step above the lap joint. Compliance per the Service Bulletin. Within 36 months. Effective July 16, 2008.
Source; http://www.airweb.faa.gov/Regulatory...2008-12-04.pdf
2011. 100 ADs - Widespread Fatigue Damage .
“Since 1988, the FAA has issued approximately 100 airworthiness directives to address WFD
Widespread Fatigue Damage in airplanes. Approximately 25 percent of these airworthiness directives were too urgent to allow the public an opportunity to comment in advance. These airworthiness directives required inspections, and the FAA later superseded the majority of them to expand the inspections or require modifications because inspections were not enough to preclude WFD. Effective January 14, 2011.” Source; Federal Register; http://www.regulations.gov/#!documentDetail;D=FAA-2006-24281-0088.
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Those (DC10 door latches) were designed and manufactured by Convair.
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By chance have just been (re) reading the 'The Comet Riddle' and although there were other defects found by flight testing the main research was concentrated around the tests performed in a water tank. The test was conducted on a whole airframe; the wings subjected to typical flight loads and the pressure vessel (ie the fuselage) was pressurized to simulate the constant ascents and descents. And as we know it was eventually discovered that there was a fatigue crack emanating from the ADF window.
As new technologies come into existence, for instance the Boeing 787, are similar 'Comet' tests conducted to ascertain how many cycles the airframe can withstand? Or is it all computer simulated?
As new technologies come into existence, for instance the Boeing 787, are similar 'Comet' tests conducted to ascertain how many cycles the airframe can withstand? Or is it all computer simulated?
Lap joints
In answer to jxk, yes new aircraft types must be fatigue tested though not now in a water tank. However B737 was never properly fatigue tested relying instead on read over from 707 and 727.
Further to my post #126, I wanted to better explain how the lap joint evolved, by posting some illustrations from NTSB report on Aloha accident. That doesn’t seem possible on pprune so those who are interested should refer to pg 15 and on of the report at: http://www.airdisaster.com/reports/ntsb/AAR89-03.pdf.
Prior to LSN 292 the outer skin at the lap was fatigue critical at top row of rivets (the most heavily stressed row), due to stress concentrations at the countersink and likely failure of the cold bond process. After LSN 292 the outer skin was locally reinforced with a hot bonded doubler. In both cases the next weakest link is fatigue of inner skin at bottom row of rivets. That's what failed on SWA aircraft. And if reports of loose rivets are true then premature failure is not surprising. What is alarming is the much greater difficulty of detecting cracks in inner skin compared with outer. There’s a further hazard in that when the inner skin starts to crack it is initially braced by the outer skin and cracks become excessively long before controlled decompression happens.
Further to my post #126, I wanted to better explain how the lap joint evolved, by posting some illustrations from NTSB report on Aloha accident. That doesn’t seem possible on pprune so those who are interested should refer to pg 15 and on of the report at: http://www.airdisaster.com/reports/ntsb/AAR89-03.pdf.
Prior to LSN 292 the outer skin at the lap was fatigue critical at top row of rivets (the most heavily stressed row), due to stress concentrations at the countersink and likely failure of the cold bond process. After LSN 292 the outer skin was locally reinforced with a hot bonded doubler. In both cases the next weakest link is fatigue of inner skin at bottom row of rivets. That's what failed on SWA aircraft. And if reports of loose rivets are true then premature failure is not surprising. What is alarming is the much greater difficulty of detecting cracks in inner skin compared with outer. There’s a further hazard in that when the inner skin starts to crack it is initially braced by the outer skin and cracks become excessively long before controlled decompression happens.
