SWA 737 Suffers Fuselage Crack

MrBretz · Sat Mar 14, 2020 5:47 am

Here’s something interesting.

https://www.bloomberg.com/news/articles ... bed-by-faa

Cracks in the fuselage? And the FAA is considering inspections?

oschkosch · Sat Mar 14, 2020 8:20 am

Luckily nothing serious happened. They managed to land safely

https://www.reuters.com/article/us-faa- ... SKBN21039D

FAA launches probe after in-flight incident reveals 12-inch crack on 737 jet

An initial inspection of the aircraft by the FAA revealed a 12-inch crack on the crown skin in an area that already requires inspections every 1,500 flight cycles. The Wall Street Journal reported the aviation safety regulator was investigating potential structural problems affecting hundreds of Boeing 737 jets.

bennett123 · Sat Mar 14, 2020 8:34 am

Would be interesting to know the hours/cycles on that aircraft.

giblets · Sat Mar 14, 2020 8:57 am

Looks like N726SW, last flight on Monday on that route . 21yrs old first flight Feb 1999. No idea on hours

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wjcandee · Sat Mar 14, 2020 9:56 am

oschkosch wrote:
Luckily nothing serious happened.

Except a partial decompression.

giblets · Sat Mar 14, 2020 10:04 am

Looks like it’s been grounded since

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StTim · Sat Mar 14, 2020 10:13 am

giblets wrote:
Looks like it’s been grounded since

Sent from my iPhone using Tapatalk

A 12 inch crack in the crown is not something that can be fixed with a bit of speedtape. This frame will be out of service for some time.

tamasm · Sat Mar 14, 2020 11:06 am

You got to love the Bloomberg article:

The Boeing Co. 737-700 involved in the Tuesday flight continued to its destination and landed without incident, Southwest said. None of the 123 passengers on board were injured. The plane is an older version of the 737, not the newer Max model that has been grounded for a year.

Obviously it wasn't the MAX

giblets · Sat Mar 14, 2020 11:39 am

StTim wrote:
giblets wrote:
Looks like it’s been grounded since

Sent from my iPhone using Tapatalk

A 12 inch crack in the crown is not something that can be fixed with a bit of speedtape. This frame will be out of service for some time.

Agree, should have made it in reply to the ‘nothing serious’ comment!

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747classic · Sat Mar 14, 2020 11:49 am

giblets wrote:
Looks like N726SW, last flight on Monday on that route . 21yrs old first flight Feb 1999. No idea on hours

Sent from my iPhone using Tapatalk

N726SW, last recorded hours/cycles at 10-14-2019 : 71941 hrs, 42590 cycles (see : FAA SDR reporting website : https://av-info.faa.gov/sdrx/Query.aspx )

Weatherwatcher1 · Sat Mar 14, 2020 12:28 pm

MrBretz wrote:

Cracks in the fuselage? And the FAA is considering inspections?

Yes cracks happen. That’s why there is a structural inspection program. Unfortunately it looks like this crack wasn’t discovered early enough. Structural parts are inspected to prevent cracks from growing to this size.

The FAA would certainly consider inspections or even modification. The FAA doesn’t come up with inspections or the proposal on how to mitigate the cracks. Boeing comes up with the inspection or modification and the FAA mandates them through an airworthiness directive.

https://www.faa.gov/documentLibrary/med ... 0.107A.pdf

dangle · Sat Mar 14, 2020 1:01 pm

WSJ reports that "according to a person familiar with the details," the aircraft's last crown inspection occurred approx 500 flights before the incident, leading to speculation that the investigation may lead the FAA to decrease the crown inspection interval from the current requirement of every 1500 flights.

https://www.wsj.com/articles/faa-consid ... lista_pos5

SuseJ772 · Sat Mar 14, 2020 1:48 pm

tamasm wrote:
You got to love the Bloomberg article:

The Boeing Co. 737-700 involved in the Tuesday flight continued to its destination and landed without incident, Southwest said. None of the 123 passengers on board were injured. The plane is an older version of the 737, not the newer Max model that has been grounded for a year.

Obviously it wasn't the MAX

I actually think this is an example of good reporting. Yes everyone on this site knows a 737-700 is not a MAX, but few in the public would. All they would hear is 737 and possibly associate the two.

kiowa · Sat Mar 14, 2020 1:50 pm

StTim wrote:
giblets wrote:
Looks like it’s been grounded since

Sent from my iPhone using Tapatalk

A 12 inch crack in the crown is not something that can be fixed with a bit of speedtape. This frame will be out of service for some time.

Where is the "crown"? I assume anywhere on the top of the fuselage?

It is also interesting that the crew did not decend below 10000 feet after a cabin pressure warning.

StTim · Sat Mar 14, 2020 1:53 pm

I assume (bad thing to do I know) that the differential pressure between inside the cabin and outside at 10,000' was not sufficient for major loss of cabin pressure. The crew will not have known there was a crack in the crown.

alangator · Sat Mar 14, 2020 1:59 pm

Crown is a general term for the uppermost skin panel.

I am really interested in how this crack is oriented and where it happened.

If I had to guess, I'd say with such a low inspection interval, that this is likely STC affected structure, likely around the wifi bubble.

SEPilot · Sat Mar 14, 2020 3:00 pm

747classic wrote:
giblets wrote:
Looks like N726SW, last flight on Monday on that route . 21yrs old first flight Feb 1999. No idea on hours

Sent from my iPhone using Tapatalk

N726SW, last recorded hours/cycles at 10-14-2019 : 71941 hrs, 42590 cycles (see : FAA SDR reporting website : https://av-info.faa.gov/sdrx/Query.aspx )

That is a pretty high cycle count. The limit is 75,000, but I would expect that few frames will reach it. I can easily understand it if the FAA were to reduce the inspection interval for planes with more than, say, 35,000 or 38,000 cycles.

kiowa · Sat Mar 14, 2020 4:00 pm

StTim wrote:
I assume (bad thing to do I know) that the differential pressure between inside the cabin and outside at 10,000' was not sufficient for major loss of cabin pressure. The crew will not have known there was a crack in the crown.

The Bloomberg article said the crew did get a warning and that prompted them to descend to 22,000 feet. Perhaps the warning went out at 22,000 feet. It just seems strange that they would stop the descent not knowing what the problem was.

kalvado · Sat Mar 14, 2020 4:17 pm

kiowa wrote:
StTim wrote:
I assume (bad thing to do I know) that the differential pressure between inside the cabin and outside at 10,000' was not sufficient for major loss of cabin pressure. The crew will not have known there was a crack in the crown.

The Bloomberg article said the crew did get a warning and that prompted them to descend to 22,000 feet. Perhaps the warning went out at 22,000 feet. It just seems strange that they would stop the descent not knowing what the problem was.

Why, they know that they can continue descent in case of a total loss of pressurization, and they would have enough consciousness time for that. Actually worst-case scenario at aircraft ceiling is just that - total loss, and it is assumed to be manageable.
Apparently, they didn't anticipate structural failure a-la Aloha 243. But anticipating THAT on the partial loss of pressure may be too much to ask.

Wacker1000 · Sat Mar 14, 2020 6:10 pm

Weatherwatcher1 wrote:
The FAA would certainly consider inspections or even modification. The FAA doesn’t come up with inspections or the proposal on how to mitigate the cracks. Boeing comes up with the inspection or modification and the FAA mandates them through an airworthiness directive.

Considering there are more 737 skin panels with ADs than without, apparently the system or the aircraft needs to change.

Cubsrule · Sat Mar 14, 2020 6:34 pm

Wacker1000 wrote:
Weatherwatcher1 wrote:
The FAA would certainly consider inspections or even modification. The FAA doesn’t come up with inspections or the proposal on how to mitigate the cracks. Boeing comes up with the inspection or modification and the FAA mandates them through an airworthiness directive.

Considering there are more 737 skin panels with ADs than without, apparently the system or the aircraft needs to change.

How peculiar is that to the 737?

cschleic · Sat Mar 14, 2020 6:56 pm

SuseJ772 wrote:
tamasm wrote:
You got to love the Bloomberg article:

The Boeing Co. 737-700 involved in the Tuesday flight continued to its destination and landed without incident, Southwest said. None of the 123 passengers on board were injured. The plane is an older version of the 737, not the newer Max model that has been grounded for a year.

Obviously it wasn't the MAX

I actually think this is an example of good reporting. Yes everyone on this site knows a 737-700 is not a MAX, but few in the public would. All they would hear is 737 and possibly associate the two.

Agree. Most readers probably would have asked themselves "...was that a MAX?..." so answering the question in the article makes sense. Looking for any reason to bash media isn't necessary.

1989worstyear · Sat Mar 14, 2020 7:00 pm

Cubsrule wrote:
Wacker1000 wrote:
Weatherwatcher1 wrote:
The FAA would certainly consider inspections or even modification. The FAA doesn’t come up with inspections or the proposal on how to mitigate the cracks. Boeing comes up with the inspection or modification and the FAA mandates them through an airworthiness directive.

Considering there are more 737 skin panels with ADs than without, apparently the system or the aircraft needs to change.

How peculiar is that to the 737?

It's also probably the oldest system on any pressurized aircraft still flying in large numbers and (until recently) being produced.

That fuselage design first flew on the -100 in 1967 :shock:

UA444 · Sat Mar 14, 2020 7:18 pm

Almost as if fuselage cracks have been a constant problem on the 737, both classic and NG.

Weatherwatcher1 · Sat Mar 14, 2020 7:38 pm

1989worstyear wrote:
Cubsrule wrote:
Wacker1000 wrote:

Considering there are more 737 skin panels with ADs than without, apparently the system or the aircraft needs to change.

How peculiar is that to the 737?

It's also probably the oldest system on any pressurized aircraft still flying in large numbers and (until recently) being produced.

That fuselage design first flew on the -100 in 1967

Incorrect. The 737 fuselage structure was Significantly changed for the 737NG. All the loads in the fuselage changed when the skin changed to allow the service ceiling to be raised from 37,000 ft on the 737-100/500 to 41,000 ft on the 737NG. The fuselage is sufficiently different that very few structural airworthiness directive mandated 737NGs inspections are also applicable to the 737 classic.

Weatherwatcher1 · Sat Mar 14, 2020 7:40 pm

Cubsrule wrote:
Wacker1000 wrote:
Weatherwatcher1 wrote:
The FAA would certainly consider inspections or even modification. The FAA doesn’t come up with inspections or the proposal on how to mitigate the cracks. Boeing comes up with the inspection or modification and the FAA mandates them through an airworthiness directive.

Considering there are more 737 skin panels with ADs than without, apparently the system or the aircraft needs to change.

How peculiar is that to the 737?

It’s not. Both the 737 and A320plus have airworthiness directives Getting published on an almost monthly basis mandating more structural inspections

https://www.faa.gov/regulations_policie ... ch/?q=a320

https://www.faa.gov/regulations_policie ... oeing+737+

smartplane · Sat Mar 14, 2020 7:48 pm

1989worstyear wrote:
It's also probably the oldest system on any pressurized aircraft still flying in large numbers and (until recently) being produced.

That fuselage design first flew on the -100 in 1967

Based on the 707, so first flew in the 50's, but with higher utilisation and many more cycles than ever envisaged when the 707 fuselage was designed.

Weatherwatcher1 · Sat Mar 14, 2020 8:26 pm

smartplane wrote:
1989worstyear wrote:
It's also probably the oldest system on any pressurized aircraft still flying in large numbers and (until recently) being produced.

That fuselage design first flew on the -100 in 1967

Based on the 707, so first flew in the 50's, but with higher utilisation and many more cycles than ever envisaged when the 707 fuselage was designed.

The 737NG May look like the 707 from the outside or for anyone who has never seen a Mylar engineering drawing, but the structure has been redesigned in CAD with more modern Structural analysis methods.

kiowa · Sun Mar 15, 2020 12:46 am

UA444 wrote:
Almost as if fuselage cracks have been a constant problem on the 737, both classic and NG.

https://www.youtube.com/watch?v=dofBk_H2wlI

kiowa · Mon Mar 16, 2020 5:27 pm

It looks like the masks did not deploy. I wonder what prompted the crew to start a rapid descent. Ears popping? Slow cabin pressure guage movement?

They also found cracks in some other Southwest airplanes when inspected.

https://www.usnews.com/news/best-states ... thwest-jet

FlyHossD · Mon Mar 16, 2020 5:35 pm

UA444 wrote:
Almost as if fuselage cracks have been a constant problem on the 737, both classic and NG.

The incidents that come quickly to my mind have been either older or high cycle airframes. Have any occurred at your (partial) namesake carrier? I don't remember any, but I haven't done a search.

lightsaber · Mon Mar 16, 2020 5:44 pm

SEPilot wrote:
747classic wrote:
giblets wrote:
Looks like N726SW, last flight on Monday on that route . 21yrs old first flight Feb 1999. No idea on hours

Sent from my iPhone using Tapatalk

N726SW, last recorded hours/cycles at 10-14-2019 : 71941 hrs, 42590 cycles (see : FAA SDR reporting website : https://av-info.faa.gov/sdrx/Query.aspx )

That is a pretty high cycle count. The limit is 75,000, but I would expect that few frames will reach it. I can easily understand it if the FAA were to reduce the inspection interval for planes with more than, say, 35,000 or 38,000 cycles.

Last I looked, limit is 100,000 cycles, 125,000 FH:

https://www.boeing.com/commercial/aerom ... 2012_q4/2/

There is an 85,000 cycle inspection on a front joint. If there is something new, please let me know. Or where you referring to a particular part life?

On a 21 year old aircraft, impressive. A little over 9 hours/day and a little under 6 cycles/day or so.

Lightsaber

Exeiowa · Mon Mar 16, 2020 5:45 pm

One approach to dealing with the MAX issue was keeping older airframes in service longer, this suggest that also has its limitations, although now overtaken by circumstances.

Bradin · Mon Mar 16, 2020 6:29 pm

It looks like some of the lessons learned and controls/remediations implemented from Aloha 243 have worked quite well. It will be interesting to see what additional lessons learned will come from this incident.

SEPilot · Mon Mar 16, 2020 9:48 pm

lightsaber wrote:
SEPilot wrote:
747classic wrote:

N726SW, last recorded hours/cycles at 10-14-2019 : 71941 hrs, 42590 cycles (see : FAA SDR reporting website : https://av-info.faa.gov/sdrx/Query.aspx )

That is a pretty high cycle count. The limit is 75,000, but I would expect that few frames will reach it. I can easily understand it if the FAA were to reduce the inspection interval for planes with more than, say, 35,000 or 38,000 cycles.

Last I looked, limit is 100,000 cycles, 125,000 FH:

https://www.boeing.com/commercial/aerom ... 2012_q4/2/

There is an 85,000 cycle inspection on a front joint. If there is something new, please let me know. Or where you referring to a particular part life?

On a 21 year old aircraft, impressive. A little over 9 hours/day and a little under 6 cycles/day or so.

Lightsaber

I searched it and found a site that said the limit for the 737NG series was 75,000 hours. But your reference is direct from Boeing, so I will accept it as being more authoritative. That says it has lived less than half its life, cycle wise (a bit more than half, hour wise). That makes it a bit more worrisome.

strfyr51 · Mon Mar 16, 2020 10:25 pm

bennett123 wrote:
Would be interesting to know the hours/cycles on that aircraft.

Oh I can bet you'll know it when the SDR comes out with the attached AD note and Service Bulletin. I would bet that airframe had a high takeoff and Landing Count on it as well. Southwest may have to step up their fuselage inspection program though they could do periodic X ray of the upper fuselage as that might be an easier than the Eddy current inspections.

Sokes · Tue Mar 17, 2020 4:17 am

Exeiowa wrote:
One approach to dealing with the MAX issue was keeping older airframes in service longer, this suggest that also has its limitations, although now overtaken by circumstances.

Do maintenance facilities face labor shortage because of the Max?

767333ER · Tue Mar 17, 2020 5:11 am

Not the first time this has happened to a 737 by any stretch of the imagination. Maybe it shouldn’t be certified for 75,000 to 100,000 cycles (or where ever in between it may be) because it seems like it’s just not cut out for that. Cracking is dangerous and shouldn’t happen. The 737 has a history of issues with this and corrosion that is slightly unnerving and Southwest now seems to be building a history of mechanical and structural failures though thankfully they’ve kept these incidents quite safe when they have happened.

It’s interesting to note that Air Canada, for example, has basically original A320s, some of which are now over 30 years old, that are up there in cycles and hours and they don’t seem to be cracking. Is it the aircraft, the company, or is this just happenstance?

Well let’s all just switch to Dash 8 classics... when it comes to structure those things seem to be basically indestructible! :lol:

LCDFlight · Tue Mar 17, 2020 5:43 am

It’s not the type of thing you would want happening, say, halfway to Hawaii. I also note this is a pattern, but how frequent a pattern, no idea, given the 10s of millions of flight hours on the active fleet.

People’s patience and sense of humor is wearing thin on the 737. Boeing has to understand that.

questions · Tue Mar 17, 2020 5:43 am

Is this similar to what caused Aloha 243?

USAirKid · Tue Mar 17, 2020 6:59 am

kiowa wrote:
It looks like the masks did not deploy. I wonder what prompted the crew to start a rapid descent. Ears popping? Slow cabin pressure guage movement?

They also found cracks in some other Southwest airplanes when inspected.

https://www.usnews.com/news/best-states ... thwest-jet

I read an article (I believe one of the ones posted up thread) on this that said it was a slow leak, so they had time to descend without the masks having to deploy.

DartHerald · Tue Mar 17, 2020 10:34 am

Did the NG fuselage design get carried over unchanged to the Max? If so, I wonder if the longer fuselage of the -10Max imposes more strain by virtue of its greater length and tendency to bend.

mjoelnir · Tue Mar 17, 2020 11:25 am

questions wrote:
Is this similar to what caused Aloha 243?

There are quite a few changes in the fuselage design between the jurassic and NG. Some changes between the jurassic and classic. Few 737 frames are used like the Aloha frame, in comparable environment. There are many more checks today looking for corrosion. So I would say it is hardly similar to Aloha 243.

IMO the limits for flight hours and cycles are rather high on the 737NG. Here we see cracks in the crown, the other day it was the pickle fork. Both issues before the frame reaches half of the anticipated life time. I would not think it strange if the high lifetime numbers, for hours and cycles, should be reduced.

Wacker1000 · Tue Mar 17, 2020 11:42 am

questions wrote:
Is this similar to what caused Aloha 243?

Everything up to later Classics had bonded skins which could delaminate and allow corrosion to occur between the layers (but this design hasn't been used in over 20 years). Either the corrosion or resulting knife-edge condition on the outer skin layer results in a lower load carrying capacity and fatigue cracking.

basspaul · Tue Mar 17, 2020 5:16 pm

An important question is if this crack was stopped by a crack-stopper part of the design? If so, that part of the design is good and prevented a catastrophic failure. I believe introducing crack stoppers was a result (or made more stringent) after Aloha 243. We will need to wait for the full investigation as to what started the crack to figure out if was a design error, manufacturing defect, maintenance error or in service damage.

IWMBH · Tue Mar 17, 2020 5:35 pm

Wacker1000 wrote:
questions wrote:
Is this similar to what caused Aloha 243?

Everything up to later Classics had bonded skins which could delaminate and allow corrosion to occur between the layers (but this design hasn't been used in over 20 years). Either the corrosion or resulting knife-edge condition on the outer skin layer results in a lower load carrying capacity and fatigue cracking.

The SWA -300's that suffered the inflight the structural failure of the fuselage skin where built in de mid-90's. Did they've the newer fuselages or the bonded skins? Otherwise, SWA can have a problem on its hands.

wnflyguy · Tue Mar 17, 2020 6:05 pm

Well WN did push some retirements back to cover the MAX8 grounding. Now with the Covid-19 planned 20% schedule cut they probably will go ahead and retire quite a few 20+ years airframes is my guess.
Flyguy

strfyr51 · Tue Mar 17, 2020 6:18 pm

StTim wrote:
giblets wrote:
Looks like it’s been grounded since

Sent from my iPhone using Tapatalk

A 12 inch crack in the crown is not something that can be fixed with a bit of speedtape. This frame will be out of service for some time.

the crown is a chemically Milled piece of aluminum the fix isn't that hard but it is time consuming and expensive . If I remember correctly? The Part alone was $150K
and that was for a 737-300. No telling what it is for a -700. and the cabin had to be opened like a tuna can. they cleared the entire cabin including the galleys and the lavs then shored the airplane up to make sure it didn't shift but the actual repair once the special Route Crew got into it took a week working 3 shifts around the clock And
the airplane wound up with nearly a completely New interior. Which is pretty much the interior United flies right today except it was the Rhapsody in Blue Paint job.

questions · Wed Mar 18, 2020 2:31 am

Wacker1000 wrote:
questions wrote:
Is this similar to what caused Aloha 243?

Everything up to later Classics had bonded skins which could delaminate and allow corrosion to occur between the layers (but this design hasn't been used in over 20 years). Either the corrosion or resulting knife-edge condition on the outer skin layer results in a lower load carrying capacity and fatigue cracking.

Thanks.

questions · Wed Mar 18, 2020 2:32 am

mjoelnir wrote:
questions wrote:
Is this similar to what caused Aloha 243?

There are quite a few changes in the fuselage design between the jurassic and NG. Some changes between the jurassic and classic. Few 737 frames are used like the Aloha frame, in comparable environment. There are many more checks today looking for corrosion. So I would say it is hardly similar to Aloha 243.

IMO the limits for flight hours and cycles are rather high on the 737NG. Here we see cracks in the crown, the other day it was the pickle fork. Both issues before the frame reaches half of the anticipated life time. I would not think it strange if the high lifetime numbers, for hours and cycles, should be reduced.

Thanks.

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