Southwest FLT 812 Decompression and diversion
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From Olasek...
"I found discussion on another forum in relation to this accident that allegedly Southwest ask their pilots to do firm landings (hard landings?). I am not going to repeat the whole line of argument how this claim might relate to this accident but I would like to verify if there is any truth in it in case there are some SWA pilots around here."
Having flown the 737 since 1990 and for nearly 10 years now at Southwest, I can assure you that I have never seen or heard of any recommendation to perform a "firm" or "hard" landing. What is in our Flight Operation Manual is common language regarding putting the aircraft in the touchdown zone and words to the effect of "do not hold the aircraft off the runway in an attempt to make a smooth landing." I think we can pretty much rule out hard landings as the cause of the skin tear.
"I found discussion on another forum in relation to this accident that allegedly Southwest ask their pilots to do firm landings (hard landings?). I am not going to repeat the whole line of argument how this claim might relate to this accident but I would like to verify if there is any truth in it in case there are some SWA pilots around here."
Having flown the 737 since 1990 and for nearly 10 years now at Southwest, I can assure you that I have never seen or heard of any recommendation to perform a "firm" or "hard" landing. What is in our Flight Operation Manual is common language regarding putting the aircraft in the touchdown zone and words to the effect of "do not hold the aircraft off the runway in an attempt to make a smooth landing." I think we can pretty much rule out hard landings as the cause of the skin tear.
Ryan
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sunfish/sevenstrokeroll
Not a sheetmetal guy but that damb DC-9 had "finger dublers". Probably lots of extra weight but internal strapping of seams made this bird tough. To pose the question if a butt joint is enough with a standard rivit pattern? Inspections of the crown of an aircraft are not very strong to date, we usually look at the floor to bildge as corrosion causes the most damage.
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I think we can pretty much rule out hard landings as the cause of the skin tear.
-drl
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grounded 27
I read somewhere that douglas used lots of rivets...more than boeing did. dc9 was slightly less fuel efficient but a heckuva lot stronger...wish I had the real data
I read somewhere that douglas used lots of rivets...more than boeing did. dc9 was slightly less fuel efficient but a heckuva lot stronger...wish I had the real data
I read somewhere that douglas used lots of rivets...more than boeing did. dc9 was slightly less fuel efficient but a heckuva lot stronger...
Was this before or after they added the extra rivets?
Last edited by TURIN; 5th Apr 2011 at 09:35.
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"on my beloved DC9, douglas always kept an airframe in a pressure cycle tank that was double the number of the highest cycles of any active airframe.
does boeing do this for the 737?"
There are two tests done (I believe by both Boeing and Douglas in that era) that you may be referencing.
A proof pressure test is done on a completed airplane. In this test the cabin is pressurized to a much greater differential that would ever be experienced in service, and it is held for many hours. This is followed by an extensive inspection of the structure. This test is done once to show that the structure holds pressure without failures.
Fatigue testing is done in what Boeing staff called the "Iron Bird". A completed primary airframe structure is placed in a heavy steel frame and many hydraulic actuators flex the airframe to simulate flight operations. Such testing goes on for years. Pressurization is not involved in it.
does boeing do this for the 737?"
There are two tests done (I believe by both Boeing and Douglas in that era) that you may be referencing.
A proof pressure test is done on a completed airplane. In this test the cabin is pressurized to a much greater differential that would ever be experienced in service, and it is held for many hours. This is followed by an extensive inspection of the structure. This test is done once to show that the structure holds pressure without failures.
Fatigue testing is done in what Boeing staff called the "Iron Bird". A completed primary airframe structure is placed in a heavy steel frame and many hydraulic actuators flex the airframe to simulate flight operations. Such testing goes on for years. Pressurization is not involved in it.
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dear you tube poster...I can't see it due to old technology. if you are talking about the plane that the FAA inspector cracked in half, that' is a bit different, don't you think?
It is not "Hard landings" it is not "Not enough rivets" that has caused this. There are well over a Thousand B737 being "Hard landed" and "Pressurised" every hour of every day.
The aircraft is a long proven design. It was designed to "fail safe" principles which is exactly what it did in this case. We know that cracks will propagate along riveted joints. That is why tear straps are installed, and they appear to have worked exactly as designed, stopping the crack propagating beyond design limits.
By "fail safe" we mean that no single point of structural failure will be catastrophic and the failure will announce itself so that it cannot go unnoticed. Modern practice is a little different - the structures are designed to be "damage tolerant".
The issue for Southwest is not that the structure cracked. All aircraft crack, all the time.
The first issue is why this part of the structure cracked? As far as I know, this is not a known location with a history of cracking. It may be that this aircraft is a fleet leader in terms of the number of pressurisation cycles in which case other B737s may exhibit this behaviour at around that age, but my personal opinion is that this is unlikely, there may instead be a latent manufacturing defect or a botched modification or repair of previous damage that started the process. The NTSB will work it out.
The second issue is why was it not picked up? What inspections are supposed to be done? Were they done? Is the nominated inspection method adequate to detect this type of damage?
The aircraft is a long proven design. It was designed to "fail safe" principles which is exactly what it did in this case. We know that cracks will propagate along riveted joints. That is why tear straps are installed, and they appear to have worked exactly as designed, stopping the crack propagating beyond design limits.
By "fail safe" we mean that no single point of structural failure will be catastrophic and the failure will announce itself so that it cannot go unnoticed. Modern practice is a little different - the structures are designed to be "damage tolerant".
The issue for Southwest is not that the structure cracked. All aircraft crack, all the time.
The first issue is why this part of the structure cracked? As far as I know, this is not a known location with a history of cracking. It may be that this aircraft is a fleet leader in terms of the number of pressurisation cycles in which case other B737s may exhibit this behaviour at around that age, but my personal opinion is that this is unlikely, there may instead be a latent manufacturing defect or a botched modification or repair of previous damage that started the process. The NTSB will work it out.
The second issue is why was it not picked up? What inspections are supposed to be done? Were they done? Is the nominated inspection method adequate to detect this type of damage?
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Considering that airframe is 15 years old and has only limited residual value, it will probably be struck off by Southwest, sold on by the insurers, patched up, and converted into a freighter!
Cheers
Cheers
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I would like to know where the work on the ruptured plane was done one year ago. Fox implied it was outside of the US.
Just wondering if anyone knows where the last heavy mx was done. not current inspections ordered in last few hours.
Just wondering if anyone knows where the last heavy mx was done. not current inspections ordered in last few hours.
Sunfish
good points
Just to add
The latest news says the Boeing didn't expect cracks at this location and therfore only suggested a visual inspection. Of course Sothwest offers that they followed the original Boeing advice so no error on their part.
as I suggested earlier I would look for a lightswitch error in thinking about the fleet management.
possible manufacture problem
possible hard useage problem (too many cracks for too long elsewhere etc. ?)
Possible maintenace problem e.g. the AA fork lift etc.
The Boeing folks and the NTSB will likely get to this pretty quick, if it's a light switch problem. All aircraft fleets await the answer
good points
It is not "Hard landings" it is not "Not enough rivets" that has caused this. There are well over a Thousand B737 being "Hard landed" and "Pressurised" every hour of every day.
The aircraft is a long proven design. It was designed to "fail safe" principles which is exactly what it did in this case. We know that cracks will propagate along riveted joints. That is why tear straps are installed, and they appear to have worked exactly as designed, stopping the crack propagating beyond design limits.
By "fail safe" we mean that no single point of structural failure will be catastrophic and the failure will announce itself so that it cannot go unnoticed. Modern practice is a little different - the structures are designed to be "damage tolerant".
The issue for Southwest is not that the structure cracked. All aircraft crack, all the time.
The first issue is why this part of the structure cracked? As far as I know, this is not a known location with a history of cracking. It may be that this aircraft is a fleet leader in terms of the number of pressurisation cycles in which case other B737s may exhibit this behaviour at around that age, but my personal opinion is that this is unlikely, there may instead be a latent manufacturing defect or a botched modification or repair of previous damage that started the process. The NTSB will work it out.
The second issue is why was it not picked up? What inspections are supposed to be done? Were they done? Is the nominated inspection method adequate to detect this type of damage?
The aircraft is a long proven design. It was designed to "fail safe" principles which is exactly what it did in this case. We know that cracks will propagate along riveted joints. That is why tear straps are installed, and they appear to have worked exactly as designed, stopping the crack propagating beyond design limits.
By "fail safe" we mean that no single point of structural failure will be catastrophic and the failure will announce itself so that it cannot go unnoticed. Modern practice is a little different - the structures are designed to be "damage tolerant".
The issue for Southwest is not that the structure cracked. All aircraft crack, all the time.
The first issue is why this part of the structure cracked? As far as I know, this is not a known location with a history of cracking. It may be that this aircraft is a fleet leader in terms of the number of pressurisation cycles in which case other B737s may exhibit this behaviour at around that age, but my personal opinion is that this is unlikely, there may instead be a latent manufacturing defect or a botched modification or repair of previous damage that started the process. The NTSB will work it out.
The second issue is why was it not picked up? What inspections are supposed to be done? Were they done? Is the nominated inspection method adequate to detect this type of damage?
The latest news says the Boeing didn't expect cracks at this location and therfore only suggested a visual inspection. Of course Sothwest offers that they followed the original Boeing advice so no error on their part.
as I suggested earlier I would look for a lightswitch error in thinking about the fleet management.
possible manufacture problem
possible hard useage problem (too many cracks for too long elsewhere etc. ?)
Possible maintenace problem e.g. the AA fork lift etc.
The Boeing folks and the NTSB will likely get to this pretty quick, if it's a light switch problem. All aircraft fleets await the answer
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The first issue is why this part of the structure cracked? As far as I know, this is not a known location with a history of cracking. It may be that this aircraft is a fleet leader in terms of the number of pressurisation cycles in which case other B737s may exhibit this behaviour at around that age, but my personal opinion is that this is unlikely, there may instead be a latent manufacturing defect or a botched modification or repair of previous damage that started the process. The NTSB will work it out
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FAA issues new AD
You can read the new AD in response to this incident here. The AD requires eddy current testing to find and confirm cracks in the lower skin at the lap join lower fastener row at 2 specific stringers along a rather long section of the aircraft fuselage in aircraft having over 30000 cycles. For those of you concerned about airframe age, note there is nothing in the AD about how old the aircraft is - just how many cycles. Also of note, SWA aggressively keeps their planes in the air (and making money) and has many short routes. IMHO the combination of these factors likely results in SWA having a higher # of cycles for a given age airframe than other carriers. It would be most interesting to know how this ratio varies across carriers. I wonder if the FAA has that stored away in a database somewhere.
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Boeing never expected failures in the riveted skin joints running along the top of the 737-300, 737-400 and 737-500 models until the planes were much older, said Paul Richter, Boeing's top engineer for older 737s.
Richter said Boeing also didn't anticipate the need to inspect for cracking on the redesigned lap joints — where two pieces of the fuselage skin overlap — until it had reached 60,000 pressurization cycles, the number of takeoffs and landings.
And it certainly didn't expect such a dramatic failure, he said.
Richter said Boeing also didn't anticipate the need to inspect for cracking on the redesigned lap joints — where two pieces of the fuselage skin overlap — until it had reached 60,000 pressurization cycles, the number of takeoffs and landings.
And it certainly didn't expect such a dramatic failure, he said.
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AS I said before this is not an old aircraft. It is about half its life.
It will not be the fleet leader as the first 300s came on line in the mid 80s.
Southwest have lots of quite short flights for the US but I bet the average cycles per hour are higher in some european airlines.
A big part of the concern is that this is a big problem for a mid life aircraft used in a normal way.
It will not be the fleet leader as the first 300s came on line in the mid 80s.
Southwest have lots of quite short flights for the US but I bet the average cycles per hour are higher in some european airlines.
A big part of the concern is that this is a big problem for a mid life aircraft used in a normal way.
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