Southwest 737 lands at Yeager Airport after hole in fuselage

[KD4CVT]

Monday July 13, 2009
Southwest 737 lands at Yeager Airport after hole in fuselage
by The Associated Press




CHARLESTON, W.Va. -- A Southwest Airlines 737 aircraft made a emergency landing in Charleston after the passenger cabin became depressurized after a hole appeared in the fuselage.


Central West Virginia Regional Airport Authority spokesman Brian Belcher says Flight 2294 was diverted to Yeager Airport and landed shortly after 6:30 p.m. Monday. There were 126 passengers and five crew members on board.


Southwest spokeswoman Marilee McInnis said the football-sized hole was located mid-cabin, near the top of the aircraft. McInnis said a replacement plane was to take the passengers to Baltimore.


Belcher says the plane, which left Nashville about 4:15 p.m. CDT and was headed to Baltimore, landed without incident. No one was injured.


The National Transportation Safety Board is trying to determine what might have caused the damage, McInnis said.

[Airbubba]

Here's the divert from FlightAware:

FlightAware > Live Flight Tracker > Southwest Airlines Co. #2294 > 13-Jul-2009 > KBNA-KBWI (http://flightaware.com/live/flight/SWA2294/history/20090713/2115Z/KBNA/KBWI)

Looks like they were almost to FL 350 when they did the high dive.

[DocSullivan]

The story so far:

Southwest Airlines B737 with hole in fuselage lands safely at Charleston, WV (http://aircrewbuzz.com/2009/07/southwest-airlines-b737-with-hole-in.html) - AircrewBuzz.com

Photo (posted via Twitter): Twitpic - Share photos on Twitter (http://twitpic.com/a9vk8)

(Yikes! :eek:)

[Graybeard]

If it has Arinc 700 ADF, that's about where the loop/sense antenna would be. There would be a hole about 3" diameter for that, IIRC.

GB

[protectthehornet]

recall the FAA's fines against Southwest for cracks?

while we don't have enough details, from my experience , this airport is a tough one.

to chose it for an emergency landing means things were bad and THEY needed to get down somewhere pronto.

[SeniorDispatcher]

>>>to chose it for an emergency landing means things were bad and THEY needed to get down somewhere pronto

Or, it could just as easily mean that CRW just happened to be the nearest suitable airport as of the time the event occured. The Flightaware track would tend to support that...

[protectthehornet]

charley west is a tough airport...if things were ok...they could have gone for another half hour and had some great airports

its ok, I've flown there for 10 years...but if something was wrong with my plane, I would go elsewhere...UNLESS....

[vapilot2004]

SOUTHWEST AIRLINES INFORMATION REGARDING FLIGHT 2294

Scheduled Nashville-Baltimore Flight Diverts to West Virginia

DALLAS, TX—July 13, 2009—Southwest Airlines confirms Flight 2294, the 4:05 pm Eastern scheduled departure from Nashville to Baltimore/Washington diverted to Yeager Airport in Charleston, W. Va at approximately 5:10 pm Eastern today after a cabin depressurization. All 126 passengers and crew of five onboard landed safely and are awaiting a replacement aircraft in Charleston that will take them to Baltimore/Washington International Airport later this evening.

The aircraft cabin depressurized approximately 30 minutes into the flight, activating the passengers’ onboard oxygen masks throughout the cabin. Medical personnel in Charleston assessed passengers and no injuries are reported. Southwest Airlines is sending its maintenance personnel to Charleston to assess the aircraft, and the airline will work with the NTSB to determine the cause of the depressurization. According to initial crew reports, the depressurization appears to be related to a small-sized hole located approximately mid-cabin, near the top of the aircraft.

There is no responsible way to speculate as to a cause at this point. We have safety procedures in place, and they were followed in this instance to get all passengers and crew safely on the ground. Reports we have are that our passengers were calm and that our Pilots and Flight Attendants did a great job getting the aircraft on the ground safely.

In an abundance of caution, we have initiatied an inspection of all 737-300s tonight. We expect only minimal impact to tomorrow's schedule until all of those inspections are complete.

[DingerX]

Oh come on Hornet, maybe the flight crew were ex-Navy, and thought, worse case, the crash barrier would keep them on the hilltop. Or maybe they were ex-Colgan based in CRW, and not only could they do the approach in their sleep, they probably already had. :P

State capital has some decent medical facilities that are only a winding drive up the mountain away -- I think they're even on the same part of town. The ANG is based in CRW, which should help disaster relief anyway.

But for a less severe incident, you're probably right. The airport bar is not very impressive, and there are no good restaurants in town. On the bright side, it sounds like they can get a stack of pizzas on-site with minimal delay. I suspect there are very few other places in the world where you'll see such flexibility and heroism from the region's catering assets.

[barit1]

CRW is an interesting landing strip. Fifty years ago my father had a forced landing there - water in the avgas. The engine quit on short final - 30 seconds sooner and he'd been into the hillside.

Oh, and there are some reasonable restaurants there, but not for 126 pax plus crew. :}

[blueloo]

Not knowing anything about the airport - why is it regarded as tough?

(Just curious)

[avionicsmoke]

After viewing the photo,s it appears that the hole has regular edges as if it is a panel that has partially detached! As I do not know the aircraft type I could be totally wrong! :hmm:

[FlyingDOM]

There are 4 airports north, south, east and west of CRW ranging from 64nm to as little as 42nm from CRW each of which have an ILS and longer runways than CRW. However, as most of us know, each airline has a list of airports that it considers acceptable alternates (or first choice alternates) and more than anything else has to do with that airline having it's own ops office there so they can handle their own passengers and not have to rely on another airline to do it. This is probably even more so with SWA because they don't have agreements with other airlines, or at least not as many as most of the majors do. Kudos to the crew members for doing a great job of putting her on the ground safely with no injuries.:ok:

[PaperTiger]

Sorry, that ain't a small hole.

No antenna in that location:
JetPhotos.Net Photo » N387SW (CN: 26602) Southwest Airlines Boeing 737-3H4 by Jason Whitebird (http://jetphotos.net/viewphoto.php?id=5822812&nseq=11)

[avionicsmoke]

Agreed,it would be an odd place for a panel but what about a poor quality skin repair?
Does anyone else think the hole edges look too uniform to be true?

[Ares]

Video with passenger account, outer views of aircraft: Jet makes landing with football-sized hole - CNN.com (http://edition.cnn.com/2009/US/07/13/us.jetliner.damaged/index.html#cnnSTCVideo)

[llondel]

The BBC now have a report at BBC NEWS | Americas | Hole in US plane forces landing (http://news.bbc.co.uk/1/hi/world/americas/8150346.stm) with a picture of someone looking at the aircraft from the outside that shows nicely where it is (just in front of the vertical stabiliser).

They missed the obvious headline though: "Hole appears in aeroplane; investigators are looking into it".

ETA: it seems to be remarkably square. I bet it ruptured and then tore along the approved lines as Boeing intended with their design.

[yssy.ymel]

If I remember correctly, the engineering for the airframe has some built in safeguards - if there is hole punched in (or out of) the airframe, a panel around this size is the maximum that should detach. What happened here is the exact opposite of what occurred in the Aloha Airlines flight (243 if I remember correctly). If that's the case, the airframe responded correctly to the failure, and (albeit there were no fatigue cracks in this airframe) half the cabin didn't peel away. A good outcome none the less.

[Will Fraser]

Then again SWA was spanked by the FAA last Fall for deferring non deferable skin inspects. ".......who ya gonna call...."

Will

[Two's in]

Not their week - They just had an APU fire indication and evacuated on the Runway at Orlando (via stairs)

Flight Makes Emergency Landing At OIA - Orlando News Story - WKMG Orlando (http://www.clickorlando.com/news/20050106/detail.html#)

PS. Edited to say that this incident warranted 3 news helicopters over the field for the last hour - clearly a slow news day.

[yssy.ymel]

Thank $DEITY it wasn't an Airbus.... :}

[West Coast]

Charley West does have some challenging aspects but nothing to the point of overflying it if they needed down pronto, especially so if the crew was familiar with the airport.

It's no Aspen.

[Love_joy]

yssy.ymel (http://www.pprune.org/members/294885-yssy-ymel), to speculate for just a minute - I would guess you hit it right on there.

Being a SWA -300, I can only imagine that it is a high cycle airframe. Despite the best safeguards in place, fatigue related failure can occur when least expected.

As stated, the uniform shaped hole suggests that the tear strips did their job.

Now what would have happened if a pax/hostie had been stood under the hole a la the Aloha incident....

[con-pilot]

I agree with West Coast, Charley West is a bit intimidating, mostly because it does look like you are landing on an aircraft carrier, granted a very long aircraft carrier. However, as he stated it is certainly no Aspen.

I have landed 727s and other smaller jets at CRW a few times, however, I am much more familiar with ASE. I'm sure the reason why they landed at CRW will come out in the near future.

But to be very honest, CRW would not have been my first choice, but then again, I was not flying the aircraft. I'm sure they had a very valid reason and I'm not going to second guess the crew.

[DozyWannabe]

Being a SWA -300, I can only imagine that it is a high cycle airframe.
Registration N387SW
Serial 26602
Line Number 2627

First Flight 16.06.94
Delivery Date 29.06.94

Airframe is apparently 15 years old. Not particularly elderly...

[L-38]

After viewing the photo,s it appears that the hole has regular edges as if it is a panel that has partially detached!

Good picture - you can even determine the (empty) edge rivnut's with their proper spacing - all indicative of a missing plate or antenna patch.

What? . . . No fatties sucked out James Bond style as in the movies?

[IGh]

Someplace there's a photo of a similar fuselage SKIN failure, on a B727. I can't find the photo, I see there are several B727 cases that read about the same as this B737 case, eg:

= = = \/ = = =

ASIAS BRIEF REPORT... ACCIDENT AND INCIDENT DATABASE
Report Number: 19881226056139C
Local Date: 26-DEC-88
City: CHARLESTON
State: WV
Airport Name: YEAGER
... MINOR
Aircraft Make: BOEING
Aircraft Model: 727-200
... Airframe Hrs: 68035
... EASTERN AIR LINES
NARRATIVE

AIRCRAFT EXPERIENCED RAPID DECOMPRESSION. EMERGENCY DESCENT AND LANDED. FUSELAGE SKIN FAILURE CAUSED PROBLEM.

and

CHI87IA067 January 25, 1987 B727-122, : N7015U EXTERIOR SKIN FAILED IN FATIGUE ... CRUISE ... LOST CABIN PRESSURE .... MASKS AUTOMATICALLY DEPLOYED.

[Will Fraser]

68,035 hours TT

That's TEN YEARS airborne, god knows cycles. That's all?? :ok::ok:

[smith]

aerial picture of CRW

File:20090121 0693 Yeager Airport.JPG - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/File:20090121_0693_Yeager_Airport.JPG)

[greuzi]

Well all's well that ends well. Post 2 shows somebody made a very definite decision and did a good job of slowing it all down in time. I agree with an earlier poster that at least one of the crew was probably familiar with the airport, and even if not, I still don't think it the worst decision ever made.

[quant]

The US carrier Southwest Airlines has inspected about 200 planes after a hole opened up in the passenger cabin during a flight, forcing an emergency landing.

BBC NEWS | Americas | Hole in US plane forces landing (http://news.bbc.co.uk/1/hi/world/americas/8150346.stm)

:8

[protectthehornet]

two things

one, does anyone have the full report on the 727 that had something similiar happen to it? will you post it?

two: alot has been made of my post questioning CRW as an emergency airport. I meant it as a thought provoker. IF the plane could have kept going to a better airport, the crew would have. So, I am saying that things might have been worse then they appeared.

[Sonic Bam]

yssy.ymel and Love_Joy
As somebody with a bit of experience of 737 Classic heavy maintenance I completely agree with you - fatigue crack. I've seen cracks around there before but not in that exact location. Size of the hole looks to me pretty much as per the tear straps.

[furloughed_again]

I've been into CRW several times with the 737NG. No sweat, no fret, piece-a-cake.

[TURIN]

Thank $DEITY it wasn't an Airbus....

OK I'll bite.

Why would an Airbus have been a bigger problem in this case?:confused:

[EISNN]

Yeah, I have to ask too. What would be different if it was an Airbus 318/19/20/21? I'm not mech or engineer so it's a sheer curiosity.

[kenhughes]

Is it possible that yssy-ymel was thinking of the publicity bandwagon that would have started to roll:- "Yet Another Airbus Disaster/Near Disaster" sort of thing in the world's tabloids (and possibly even here on PPRuNe, perish the thought)?

[yssy.ymel]

That's it Ken. It appears every time there is an incident involving an Airbus airframe, there is a hurricane of s:mad:t produced linking each and every Airbus incident with each other.

Ill informed, unprofessional reporting by the media, and some pretty silly discussions on here don't help much either.

[Will Fraser]

Wouldn't such comment be not fact based? Where is the skin on Airbus implicated in failure? Fatigue is associated with metals, yes? At least in this case, AB would get a pass, especially here ??

Will

[ankh]

> Now what would have happened if a pax/hostie had been stood > under the hole a la the Aloha incident.... Well, fair question; would that have plugged this hole, or caused it to get bigger? (I realize we won't know unless they test this somehow ...)

[Old Engineer]

Hornet is right, if you land a 737 at CRW, it's a real emergency. I don't think it's changed from the mid-60's. 5000-foot runway; that's 2000 under jet minimum. Lower than the mountains on either end because they cut off the top of one of the endless, even, flat-topped mountains to build it. Fog in the morning on a regular basis.

The embankments at either end fall away at at least 2 vertical to 3 horizontal. Zilch overrun. An A/C had gone off the end sometime before; dim memory but I think it was an ANG boxcar. Airline tests with 4-engined prop planes led to almost another disaster, if I recall (possibly it was a Connie they tried). So Eastern continued with the Martin (404?), and there was a similar Convair some flew. I think CRW was the only reason those ancient birds were still flying.

I flew in with an Eastern pilot on one engine one morning-- carburator. Fixed. Same captain and plane going out that night. Engine fire on start-up. Quietly pointed it out to the F/A. Nothing wrong reassurance. Anyway, the Captain had seen it after all. Both bottles, he said blandly, seconds later. Told me he had never lost an engine in 20 years of flying, and here he'd lost two the same day. The Electras solved this problem in style, for a while at least.

There was a plan in those days to cut down the next mountain and throw the rock into the gap to get a really long runway. It was 24 million cubic yards of cut, most of it rock, most could be ripped I think, but still 3 or 4 dollars a yard. And what couldn't be, blasting at 10-15 dollars. That was really a lot of money then, and I don't think it was ever done.

BTW, CRW must be right under an airway. Went right over it a bit ago. That might explain the choice-- could have been closest with no diversion required, nearly straight in.

OE

[cringe]

On the two B727 incidents referenced in IGh's post:

NTSB Safety Recommendation (http://www.ntsb.gov/recs/letters/1989/A89_79_80.pdf)

It is believed that in both incidents the scratch or score damage to the surface of the fuselage skin was probably caused by maintenance personnel Using improper tools in marking the metal while performing a repair to the structure.

[411A]

Shades of many years ago, on B707 aircraft, both long and short body.
Fuselage crown skin cracks found, altho in these past particular cases, straps were riveted on for 2500 cycles, then reskinning was necessary.

Not especially impressive for this airline, nor the airplane.:(

[North Stand Tier3]

Looking at the pics on Flight International the hole appears to be above the lapjoint at S-4L. 737CLs of this age are subject to at least 2 Service Bulletins looking for cracking or delamination of the bonded doublers (installed on older Classics) in the lapjoint areas. The repeat inspections intervals are quite stringent with the two I can think of - one requires a repeat two method NDT inspection at the same time as a detailed visual inspection. The wording of both is quite clear that failure in these areas could result in loss of structural integrity. Since the Aloha accident Boeing have been very active with any possible damage to the tear strap design of their skins on the 737CLs - I can't speak for other types though

Think all should be thankful this wasn't any worse - it could quite easily have been

Now..you ain't seen me,right.........

[Sonic Bam]

Doesn't look like anything associated with lapjoint scribe mark inspection to me, completely different failure mode.

A lapjoint scribe failure would be a rip along rivet holes al a Aloha (there has been no reported failure at a lapjoint caused by a scribe mark as far as I'm aware before people jump on this).

From the external photo (link posted earlier) it looks like a skin fatigue crack has developed and quickly run out to the chemi-etched tear strap on the internal surface of the skin then continued round the edge of the tear strap AS IT IS DESIGNED FOR.

The crown skin is inspected regularly - external general visual inspection (GVI) each C Check, internal GVI each second C Check, is NDTed at 35,000 cycles with a repeat NDT each 4,500 cycles (I think). Cracks can develop between inspections though and that is acceptable given the design of the skin and this incident bears this out.

Disclaimer - All the above is my opinion only based on experience and a couple of published photos not a physical look at the aircraft. I could be completely wrong.:8

[Graybeard]

SWA pilots get practice at KSNA every day. It's 5,700 feet. 757s are preferred by most carriers, as flights are limited by noise considerations.

GB

[protectthehornet]

KSNA is not on a mesa surrounded,closely, by hills.

[zerozero]

Not to mention Alaska Airlines and MarkAir used to take 737-200s into Dutch Harbor, Alaska.

http://www.alaska.faa.gov/fai/images/AKPEN/DUT-b.jpg

[Carrier]

Quote: “Hornet is right, if you land a 737 at CRW, it's a real emergency. I don't think it's changed from the mid-60's. 5000-foot runway; that's 2000 under jet minimum.”

7,000’ is nowhere near the minimum!
Canadian North and its predecessors, Canadian Airlines International and Pacific Western Airlines, normally operate B737s on shorter runways. The runways at Hay River, Inuvik and Fort Smith are 6,000’. The runway at Norman Wells is 5,997’. The two runways at Edmonton City Centre are 5,700’ and 5,868’. The gravel runway at Resolute Bay is 6,500’ and the gravel runway at Cambridge Bay is 5,000’. For approximately three decades the B737s have operated scheduled services to these places with no problems, including during genuine arctic winter conditions.
Last month a colleague observed three Canadian North B737s operating at Medicine Hat, which has a 5,000’ runway. They were apparently on a troop-carrying military charter in connection with CFB Suffield.

[oceancrosser]

“Hornet is right, if you land a 737 at CRW, it's a real emergency. I don't think it's changed from the mid-60's. 5000-foot runway; that's 2000 under jet minimum.”

7,000’ is nowhere near the minimum!
Canadian North and its predecessors, Canadian Airlines International and Pacific Western Airlines, normally operate B737s on shorter runways. The runways at Hay River, Inuvik and Fort Smith are 6,000’. The runway at Norman Wells is 5,997’. The two runways at Edmonton City Centre are 5,700’ and 5,868’. The gravel runway at Resolute Bay is 6,500’ and the gravel runway at Cambridge Bay is 5,000’. For approximately three decades the B737s have operated scheduled services to these places with no problems, including during genuine arctic winter conditions.
Last month a colleague observed three Canadian North B737s operating at Medicine Hat, which has a 5,000’ runway. They were apparently on a troop-carrying military charter in connection with CFB Suffield.

Off topic, but we operate 757s into 5200' runways regularly.

[RoadMaster9]

Not sure what the CRW comments are all about...

CRW has an ILS approach to both runway 5 and runway 23.

Runway 5/23 is 6,302 feet long, GS length is 5,126 or 5,435 - not a problem.

Here's how an airline pilot does it:

First, you fly the ILS procedure.
Second, you land and stop the aircraft.

Mountains have nothing to do with anything. If I were flying this aircraft and had established no other probs with the airframe, I would have probably landed at the same place. NBD...

As far as short airports go, SWA operated into DET airprort for several years in night/all wx conditions.

Length? Runway 15/33 from GS is 4,021 or 4,125 feet. Width? 100 feet.

NBD...

[p51guy]

Most checklists involving engine failures, smoke and explosive depressurisations include land at nearest suitable airport, especially on two engine aircraft. The FAA would ask you to justify why you chose not to do that. Wx, familiarity and other reasons could justify it but if the nearest suitable airport is available and safe the FAR's say to land there.

[wes_wall]

Zilch overrun. An A/C had gone off the end sometime before;

Capital Airlines in either late 1950s or early 1960s lost two airplanes in the same day - a Viscount near BAL, and a Connie at CRW, off the end of the RWY.

[Will Fraser]

Bonger

I could have framed it better. Seems ballsy to eat a big fine, suffer the pr poison, and then fly with actual issues.

[Graybeard]

Do SWA still use 3rd party for all heavy maintenance?

[BEagle]

Thank $DEITY it wasn't an Airbus....

OK I'll bite.

Why would an Airbus have been a bigger problem in this case?

Regrettably, there would have been ill-informed redneck bolleaux about "They'm goddam French airplanes ain't built as good as Bubba Boeing don' bin doin' back at th' ol' red barn" or similar. Which would have detracted from an intelligent thread as it would inevitably have led to the usual single digit IQ mud-slinging rubbish.

Hole in the jet = land asap. No fart-arsing around with 'Threat and Error Management' or other such huggy-fluffy bull$hit. Nearest suitable will do, get it on the ground without delay, talk about it later over a beer. Another 30 min might have proved catastrophic - or it might not. You might want to gamble, I wouldn't.

Well done to the crew!!

[BOAC]

Exactly! Once it starts 'tearing along the dotted line' I don't want to be 'up there' in it wishing I was 'down there'. Its a no-brainer.

[Will Fraser]

Perhaps someday a cf like this will grow some legs and improve "safety".

[protectthehornet]

roadmaster9

mountains don't make a difference

you have never flown near mountains.

I didn't say CRW was bad, I just said that if you could fly a few more minutes you would be a much better fields.

here you have a plane that is damaged...to what extent? unknown to the pilots.

what if a system designed for stopping the plane had been damaged? (not in this case as it turns out, but you don't know till you see things for yourself)

there are 13 special airports in the usa...most all of them have mountains nearby. I've flown to many of them...it does make a difference.

SWA went off the end at Midway and the runway is longer there.

[vapilot2004]

Airframe is apparently 15 years old. Not particularly elderly...



For aircraft fatigue, age is not the primary issue. Cycles are.

[kappa]

....each airline has a list of airports that it considers acceptable alternates (or first choice alternates) and more than anything else has to do with that airline having it's own ops office there so they can handle their own passengers and not have to rely on another airline to do it.
Southwest has no ops at CRW. They flew in a plane to take the pax to BWI, arriving 4 hours late.

[metrojet]

c'mon guys -

Good old Piedmont airlines flew 737-200's into CRW for many years!

Yeah, you have to be on your game going in there, but that's about it - unless the runway had snow on it.

Metrojet

[p51guy]

Choosing that airport was a decision they made quickly. If it was legal for them to land there they were correct in landing there. We can second guess all we want but when you are dealing with an emergency you have to have a plan and they had one. They were legal and safe.

[DozyWannabe]

For aircraft fatigue, age is not the primary issue. Cycles are.
Aye, am aware. :)

I was mistakenly under the impression that N73711 (at the time the second-highest cycle 737 airframe in the world) only let go after considerably longer.

J.

[Sonic Bam]

Bingo!

"scoring or scribe lines"

Today Show video (http://today.msnbc.msn.com/id/26184891/26411480#31920177)

Now comes the real question. Why is Southwest still flying these planes if they know about the "scoring or scribe lines"???????????


NTSB field guy says "We're going to be looking for corrosion, .... cracks, ...., scoring or scribe lines". Of course that's what they're going to be looking for, all of the above. Why jump on "scoring or scribe lines"? My opinion is that it is unlikely to be scoring or scribe lines but that's just my opinion.

An aircraft can quite safely fly with with a score or scribe line and most already do. Any score, scribe, crack, dent, ding or corrosion discovered in day to day operation or even maintenance should / will be cleaned up, measured and assessed against published limits (Structural Repair Manual, SB, AD, etc.). If inside these limits an inspection program and "repair by" limit is then set or it may even just be reprotected and recorded.

If it is outside published limits then you carry out the repair specified or you can go to the TC holder and ask if repair can be deferred to a more suitable time or if there is an interim repair with full repair at a later date. The TC holder may come back with some immediate repair actions, an inspection program and final fix date, or they come back with a "repair before next flight".

The AD mentioned, if I am thinking of the same one, is looking for scoring or chafing of the fuselage skin where the (removable) dorsal fin that runs forward of the vertical stab caused by the dorsal fin vibrating where comes into contact with the skin. The location of the hole in this aircraft is forward of the area the AD applies to. Red herring.

The reporter says 11 cracks were found on the aircraft during maintenance last year. A bit of sensationalism going on there. That's no big deal - that's why you have a maintenance program and inspectors. For an aircraft that age and if it is high cycles then 11 is pretty good, perhaps even on the low side. Whoops, set things up now for the "poor maintenance" nay-sayers.

[wileydog3]

Capital Airlines in either late 1950s or early 1960s lost two airplanes in the same day - a Viscount near BAL, and a Connie at CRW, off the end of the RWY.

First, the length of the runway is not so much the issue. The landing illusions are the prime consideration and the winds are next. Landing on 23 you have rapidly rising terrain and initially you appear very high and when the terrain upslope begins, it looks as if you are descending rapidly. The runway slope and the airfield on top of the plateau add to the distorted image. We went in their often in the YS-11, 737 and 727 at PI.

The thing that surprised me the most about CRW was on a run downtown and there on the river was a huge Coast Guard cutter. It had come up from the Gulf on the Mississippi and then the Ohio. I think I have my geography right but the rivers are navigable all the way to Pittsburgh. ??

The Capital Connie went down the hill backwards.
Charleston, WV Air Liner Slides Off Runway, May 1959 | GenDisasters ... Genealogy in Tragedy, Disasters, Fires, Floods (http://www3.gendisasters.com/west-virginia/4143/charleston,-wv-air-liner-slides-runway,-may-1959)

http://www.century-of-flight.net/Aviation%20history/coming%20of%20age/usairlines/images/3pln2170.jpg

[Domi]

Sonic Bam, it seems that at the location of the hole, there is an antenna on some aircraft. In that particular case, the antenna is used for ELT.
Do you know is there is any structural provision for antenna installation on B737 ? (or repair, or plug due to antenna removal on this acft ?)

Edit : well, disregard this message :}

[Loose rivets]

As soon as the skipper realized that there was structural damage, he may well have felt that it was a good idea to get his charge on the ground. Seems reasonable.

I would have been loathe to send anyone back there to brief me on the damage, or indeed have anyone unstrapped, so One would have had to assume that it was serious.

However, the counter argument might be that knowing the integrity of the hull was compromised, he should then treat the aircraft like glass, and get - 45NM? - to a less demanding field, reasoning that any vigorous control movements might just possibly exacerbate the structural problem.

His call.

[24victor]

This might be why they're looking at scribe lines;

http://www.ntsb.gov/Pressrel/2009/SW-737-interior.jpg (http://www.ntsb.gov/Pressrel/2009/SW-737-interior.jpg)

http://www.ntsb.gov/Pressrel/2009/SW-737-exterior.jpg (http://www.ntsb.gov/Pressrel/2009/SW-737-exterior.jpg)

Rgds.

24V

[protectthehornet]

my original comment about selecting CRW as an emergency airport was meant to make people think.

think twice about where you go...you may take a near disaster and turn it into a full fledged disaster.

I've landed the DC9 at CRW many times. In all weather. No one I ever flew with was casual about a landing or takeoff from this airport. We planted it and got into reverse pronto...but using brakes as needed...you see if you were on a quick turn and your brakes were hot, you might sacrifice abort performance on a quick takeoff.

There are many things a really good pilot should be considering at all times.

KPIT is about 140 miles from CRW...about 20 minutes more flying time...I might have gone there...better runways, better CFR, some of the best hospitals in the world, and perhaps most importantly...BETTER PIZZA in the vicinity of the airport (kidding). Time critical...sure go to CRW...or even HTS.

With structural failure, I might have done a slower descent too!

and Wiley...the rivers of america are amazing. I've seen big ships there just as you have. Heck, aircraft carriers have gone to chicago for gosh's sake!~

so again, good job to the crew...but now we are just talking, thinking about ''what if'' for our own use in the future.

If I thought a plane was coming apart, I wouldn't hesitate to land on a stretch of interstate...it is said that every 50 miles along the interstate, there is at least a 5000' straight patch that could serve as a runway.

Indeed, many european nations have plans to use their freeways/autobahns as runways during war emergency.

[Rigga]

Just guessing - but looking at the shape of the tear and the way it follows the backing plate profile - I'd be looking for a pencil line or some graphite trace on the inner face of the torn skin.

Rigga

[DocSullivan]

Pres release that accompanied the photos posted above by 24victor:


************************************************************
NTSB ADVISORY
************************************************************

National Transportation Safety Board
Washington, DC 20594

July 16, 2009

************************************************************

NTSB RELEASES PHOTOS OF DAMAGED SECTION OF SOUTHWEST
AIRLINES 737 FUSELAGE

************************************************************

In its continuing investigation of the Southwest Airlines
737-300 (N387SW) that experienced a rapid decompression
during a flight from Nashville to Baltimore on July 13,
2009, NTSB Acting Chairman Mark V. Rosenker has authorized
the release of two photographs showing the compromised
section of the area of the fuselage that failed in flight.

The damaged aircraft skin section was visually examined in
the NTSB's Materials Laboratory. The damage left a hole
measuring approximately 17 inches by 8 inches. The skin in
this area of the fuselage is 0.032 inches thick with an
additional 0.032 inch thick layer bonded to the interior
surface in selected areas.

Rosenker said that the initial visual examination found the
fractures in good condition and suitable for further
analysis. No significant corrosion or obvious pre-existing
mechanical damage was noted. A detailed metallurgical
examination of the skin section and the fracture surfaces
will be accomplished by the Safety Board in the coming days.

Southwest Airlines is now in the process of repairing the
aircraft at Yeager Airport, Charleston, West Virginia.

Section of fuselage skin facing inside the aircraft:
http://www.ntsb.gov/Pressrel/2009/SW-737-interior.jpg

Section of fuselage skin on exterior of aircraft
http://www.ntsb.gov/Pressrel/2009/SW-737-exterior.jpg

###

Media Contact: Peter Knudson
[email protected]
(202) 314-6100

************************************************************

This message is delivered to you as a free service from the
National Transportation Safety Board.

You may unsubscribe at any time at
NTSB - Mailing Lists (http://www.ntsb.gov/registration/registration.htm)

An archive of press releases is available at
NTSB - Press Releases (http://www.ntsb.gov/pressrel/pressrel.htm)

Current job opportunities with the NTSB are listed at
NTSB - Vacancy Announcements (http://www.ntsb.gov/vacancies/listing.htm)

For questions/problems, contact [email protected]

[Sonic Bam]

Wow, I stand corrected, that doesn't look like fatigue cracking to me. Somebody is in the cack.

I'll be off to mind my own business now. :O

[Old Engineer]

The thing with fatigue is that it starts with grain growth in the metal. When you see the crack, you are already far down the road to failure, because of the intense stress concentration at the knife-edged leading point of the growing crack. Visible cracks increase rapidly in length.

A paper here yesterday published a picture looking back at the tail fin. What I think to be a major factor leapt right out at me. The fin is a double airfoil. In the area of the failure, the passing air is speeding up (and thus dropping in pressure) to pass the fin. I think you'll realize that you can't have pressure at a single point that is different in two directions.

Thus locally there is a drop in pressure on the hull at right angles to this surface that failed. That is, here the pressure differential at altitude is greater that the pressure used in the fatigue life test. Fatigue is very sensitive to the pressure range, moreso that to the actual level of stress.

Fatigue life testing is (or was) done by filling a hull with water, and pressurizing the water. Rapid cycles, and no danger of flying fragments. However, the pressure applied is perfectly uniform.

Now as for the panel-like appearance of the pop-out, when you have a dome-like deformation under pressure, the stresses at the restrained perimeter edges of the dome will be something like twice the stress in the center of the dome. This is very counter-intuitive but it is so.

The rip-stoppers are the restraint, although they are somewhat yielding. That and their rectangular pattern make for a situation that is very difficult to analyze, either by math or by models such as plastics that can show visible stress patterns in special lighting. Well, I may be showing my age by mentioning such ancient methods.

NTSB will of course etch the edges of the break and make a microscopic inspection for grain growth (compared to an as rolled sample of the material). I think you will see this will show fatigue damage was present.

Back to runway length-- I apologize for just throwing out "minimum" length. I should have said "minimum design standard", which is a hole-in-the-cheese eliminator approach. An operational minimum is entirely different, of course. I'll explain why as soon as I have time. Washington National was the classic example, as FAA HQ was on this field for many years.

OE

On reflection, I realized I should not leave the impression that this (local pressure reduction) is an unrecognized problem. Crown inspections seem to me to indicate an awareness there is some problem which must be guarded against.

[The Bartender]

The skin in this area of the fuselage is 0.032 inches thick with an
additional 0.032 inch thick layer bonded to the interior
surface in selected areas.

I did NOT need to know that.... :p

[etesting2000]

Copy that! Willing to bet a beer it's "supposed" to be 2024T-6 from Alcoa or a number of people at Boeing are going to be re-crunching some numbers.

[ankh]

Quote: The skin in this area of the fuselage is 0.032 inches thick with an additional 0.032 inch thick layer bonded to the interior surface in selected areas. ---- Is that the 2 layers we see in the NTSB images, the skin and the interior layer? It looks like what I see when I open the inner seal on a bottle of vitamin pills.

[vapilot2004]

The skin in this area of the fuselage is 0.032 inches thick with an
additional 0.032 inch thick layer bonded to the interior
surface in selected areas.

I did NOT need to know that.... :p

That's 30 times heavier than the good Reynold's Wrap and nearly triple (within 1/1000th of an inch) the average thickness of what protects one from the contents of the average can of Coca Cola.

Cheers! :}

[24victor]

That's 30 times heavier than the good Reynold's Wrap and nearly triple (within 1/1000th of an inch) the average thickness of what protects one from the contents of the average can of Coca Cola.

It's also what they make airplanes out of. Could any inspector (airframe) out there comment as to whether this is a factory "soft patch"?

Rgds.

24V

[jethrotull]

Thus locally there is a drop in pressure on the hull at right angles to this surface that failed. That is, here the pressure differential at altitude is greater that the pressure used in the fatigue life test. Fatigue is very sensitive to the pressure range, moreso that to the actual level of stress.




An Extremely informative post, Old Eng.

Would oil canning be an early indication of weakness in this area of dome shaped stress concentration ? I would imagine joggled rivets could be another but then it depends on the stage of failure with ref to the Insp date.

As a Airframe Inspector i have to carry out crown skin inspections but have never come across ref material indicating the possibility of a localised diff pr causing the scenario you describe.

Cheers.

[HarryMann]

As a Airframe Inspector i have to carry out crown skin inspections but have never come across ref material indicating the possibility of a localised diff pr causing the scenario you describe.

You won't, the aerod. pressures are very small c.f. the pressurisation pressures.

That said, Old Engineer might be onto something! But it may be more to do with varying pressures, than an absolute exterior reduction. At some fuse attitudes and Mach Nos, it's possible slight (but long term, sustained) buffeting in that area, may have contributed.
Also, without going into calcs, my gut feeling is there could be a greater pressure reduction by far from the fuse running at a small angle of attack (which it can well do early in the cruise) than from any induced flow from that fin l.e.

Something else...looking at the bonded doubler and the tear strap/strip, and the area ratios of frame to panel. How much difference in fuse mass to just make the whole thing one thickness.. if that is typical of the frame pitch and longitudinal stiffeners.Yes, 200 lb is one passenger, but by heck, what a lot of fuss for a few oz per sq.ft

Remember, the DH Comet fuse skins were about 20~22 swg, just one gauge thicker and De Havilland might still be a name in Commercial Jet Transport Aviation :sad:

That said, she's a strong'un to hang together so well after that. And corrosion doesn't look to come into the equation. Old Engineer's belling-edge stress theory sounds good to me.

[protectthehornet]

seems to me I read that the DC8 used about 30,000 more rivets than the 707

wondering which airframe builder built the toughest airframes (western world)

[411A]

wondering which airframe builder built the toughest airframes (western world)

Amongst civil wide body types...Lockheed.:)
Most redundant, systems-wise?
Lockheed.

[vapilot2004]

wondering which airframe builder built the toughest airframes (western world)

Douglas had indeed built a well-deserved reputation on near bulletproof redundancy and legendary longevity through the years up and until the DC-10 came along. The design service cycle numbers bear this out in the area of longevity and airframe strength.

[Smilin_Ed]

My former employer proposed to lease a rather high-time DC-8 for a government contract. Based on a thorough inspection, the inspectors declared that they couldn't determine from the major structural members that the airframe had any time on it at all. Clearly a tough old bird.

P.S.: DC_ATE are you out there?

[skin_splice]

i dont see how boeing would use a 0.032" skin panel in this area?
thats 0.8 mm thick. if you put a 3/16 or 5/32" countersunk rivet in that
you would have a knife edge

i would expect 3.2 mm skin (maybe min of 1.6 mm).

Ive not seen bonded aluminium skin panels used before, ive worked
in this business 12 yrs as stress engineer for airbus/gulfstream

You can start of with 3.2 mm 2024 T3 or T42 (i think T42 is for stretch forming i.e. double curvature) then use chemi etching
to reduce the thickness in some areas.

Or you could use 1.6 or 1.2 mm, then use rivetted doublers of similar thicknes to increase the thickness if you didnt want to chemi etch

i.e. at window or a door cutout, there are doubler or reinforcement
patches (which is layers of skin rivetted or bolted on, to increase
the overall thickness)

[skin_splice]

This a/c was 15 yrs old, and probably due for its 3rd D-check, which is
a major overhaul. The paint is remove and skins/splice, joints fittings
lugs, panels are inspected for cracks.

The cabin is subject to around 9 psi of pressure every flight. Producing
very large hoop tensile stresses in the fuselage skins.

The more pressurisation cycles you have, the lower the fatigue life for the a/c

Cracks in the fuselage skins are permitted provided they dont reach a
critical length between inspection intervals. A normal fatigue spectrum
takes this into account, and is used when calculating what skin thickness
to use in that area. If there are skin or lap joints then these contribute
to the fatigue life. Your more likely to have a crack start at a joint (because
of hole), than in a region where there are no holes.

My opinion is that the age/ the fatigue spectrum and maintenance schedule of this a/c could have played a part.
I.e. maybe sustained short flights (high number of pressure cycles), or a number of heavy landings (which put high longitudinal tension loads in the upper skin).

who know maybe southwest were running to close to the bone on when to
do the next D-check.

[skin_splice]

there are only two wide body manufacturers left Boeing and Airbus
Boeing 777, 767, 747
Airbus: A380, a340, a330, a310, a300

lockheed tristar? i dont think there are many of them still flying pax
commerically most of them and DC10 are freighters now

[HarryMann]

Well, that BA 777 stood up well after dropping into Heathrow at something like12 to 15 ft/s ?

There may be the odd DC-6 still flying commerically (fire suppression in Canada?) :)

[blakmax]

OK we have had the usual "this brand is better" crap, and even had criticism of Airbus over a Boeing failure. Lets have an objective look at the evidence, in particular from the NTSB pictures.

Firstly, there is clearly a bonded reinforcement filling the entire bay but not splicing to the bonded fail-safe strap. This suggests that there was a known problem in the area. No manufacturer adds material as a design feature or a modification unless there is an issue. If there was not an issue discovered in later service or testing subsequent to certification testing, then the increase in section would not have have been formed in initial production, eliminating the need to add the doubler.

Secondly, the location of the crack that led to the failure is along the side of the fore-aft top fail-safe strap and also between the bonded reinforcement mentioned above. This is the thinnest section of skin between the skin+fail safe strap and skin+doubler.

Thirdly, the skin would have been designed to take the pressure loads on a pd/2t basis learnt in second year engineering. There would also be adequate design roigour (rigor for our American cousins) to allow for the ground-air-ground fatigue cycle.

Fourthly, the change in crack direction from parallel to the fore-aft structure to nearly parallel to the hoop fail-safe strap is typical of acoustic fatigue crack growth. It is not true flight-cycle fatigue or it would not change direction. The fore-aft stress is half that of the hoop stress plus or minus the fuselage bending stresses at the crown. Also, if it was true pressure cycle fatigue, it would also probably have initiated at the location of the high stress concentrations at the fasteners, not in the adjacent skin.

My assessment is that this is a case of acoustic fatigue (due to air flow disturbance at the front of the vertical stabiliser as already discussed). This was known to the OEM because of the evidence displayed by modification to incorporate the doubler. The reinforcement was added as a modification to change the local natural frequency, but resulted in a change to the local vibration mode to another mode that resulted in the small area between the doubler and the fail-safe strap being the critical fatigue area.

Acoustic fatigue is a strange beast that is not necessarily responsive to simple analysis. I have personal experience where a number of modifications changed the natural frequency to the next harmonic, or changed the displacement mode to a worse form with a consequent shortening of structural life compared to leaving it alone.

The solution is to incorporate an adhesively bonded ring-doubler on the INSIDE of the structure to eliminate the structurally weak area between the doubler and the fail-safe strap. It would also eliminate out-of plane bending associated with the change in section between the douber and the fail-safe strap. I would incorporate a damping layer as part of the modification. I would also strongly recommend an acoustic analysis of my suggestion, and an assessment of the effect on the fail-safe certification basis of the increased stiffness on adjacent bays.

Can I have STC rights for the above suggested modification? If so, my address is at my web site adhesionassociates.com

I hope this adds a level of structural discussion over and above the usual brand focussed tripe.

Regards

Blakmax

[lomapaseo]

blakmax

agree with you that's what it looks like.

It's natures way of telling you that the metal is excess structure

I've seen it addressed simply by removing the piece of metal that cracks in the first place. Unfortunately this has its drawbacks when you're trying to keep air inside :)

[skin_splice]

It is not common practice to use bonded aluminium panels as repairs.

The simplest repair would be to rivet an external doubler/patch
to the skin.

[HarryMann]

Blakmax suggests the bonded doubler is not a repair, but an attempt to detune that panel, as if there were a already known acoustic/resonance problem there.

I seem to concurr

That said, Old Engineer might be onto something! But it may be more to do with varying pressures, than an absolute exterior reduction. At some fuse attitudes and Mach Nos, it's possible slight (but long term, sustained) buffeting in that area, may have contributed.

[protectthehornet]

there is no doubt in my mind that

Douglas built the toughest/strongest airliners. (and the best flying for the pilot)

That Lockheed was a real innovator

And that the world is worse off for these two companies to be out of the airliner building biz.

[blakmax]

It is not common practice to use bonded aluminium panels as repairs.

The simplest repair would be to rivet an external doubler/patch
to the skin.

You are right, skin-splice, that it is not common practice to use bonded repairs on metallic aircraft at present, but eventually the civil world will realise that adhesive bonded repairs are far more effective and can save very significant costs compared to mechanical repairs. :ugh:
I have over thirty seven years experience with adhesive bonded repairs to metallic military aircraft. In one example, bonded composite patches were used to repair widespread stress corrosion cracking in C-130E wing planks. These repairs enabled the RAAF to be the only operator in the world to fly the C-130E through its life of type without replacing the wing planks. That has been estimated to have saved an audited AUD130 million. The USAF used bonded composite patches to repair C-141 and that saved billions compared to replacing the wing skins. Mechanical repairs were not an option because they could not meet damage tolerance requirements and did not provide adequate restraint of crack growth.

With skin as thin as the area in question on the 737, I would bet the family jewels that I could design a bonded repair that would never fail and would be stronger than the metal itself. In comparison, in a mechanically fastened repair the joint strength will always be limited by the stress concentrations caused by the fastener. Lets be clear. If tested to failure, an appropriately designed and correctly processed adhesive bond will break in the metal outside the repair. A mechanical repair would break at the fastener line at a much lower load.

There is a significant amount of data on bonded repairs to metallic structure. I suggest you look at Adhesion Associates (http://www.adhesionassociates.com) for a start.

Regards

blakmax

[HarryMann]

That Lockheed was a real innovator

And that the world is worse off for these two companies to be out of the airliner building biz.

If we're going way back when, which we're not :)
De Havillands were Redux bonding skins and stringers in 1950 on jet airliners

[Will Fraser]

And Hughes used multi layer Birch lumber laminates with Phenolic resin.
deHavilland. Mosquito?

Basically, lumber is a two phase matrix like CFRP, are we 'regressing'?

Rivets are older than all dirt.

[skin_splice]

most repairs are done by the airline approved maintenance ppl.
They only contact the a/c manufacturer when theyve got some concerns
or are unsure what to do.

Bonded composite repairs, im sure will be the norm once the a350 and 787
are well into service. Ive heard about them talking about the patches
for the 787.

I guess the conditions have to exactly right (i.e. the curing process
the mixing materials) in order that when the patch is bonded on, it
will meet the allowables that you specify it will meet.

So what Fsu can you achieve with the adhesive?

I guess the main people you should be trying to convince are the airlines
and the certification authorities, if you say it saves money? Its only a cultural thing at the end of the day.

it doesnt take long however to make a patch, drill off 15-20 holes and install
the rivets. And at least you are 100% confident that the the rivet allowable will
be spot on.

ill look at your website

cheers

[blakmax]

Hi skin-splice.

Maybe we need to start a new thread because this is getting off the subject. I'll let the moderator PM me if there is interest. I would be only too happy to start the ball rolling, probably under the "Engineers and Technicians" stream.

Bonded repairs to composite structure will definitely be the predominant repair if anyone has any inteligence at all. Unfortunately my understanding is that OEMs dumb-down SRMs to enable airlines in Bogloviastan to still perform repairs so much of the repairs to new composite structures will be by mechanical fastening, despite the disasterous strength loss due to tear-out weakness of composites.

I have great concerns about some SRM repairs. Injection repairs for disbonds can never under any circumstances provide an ounce of structural integrity for example, yet they remain the standard repair in SRMs. I defy anyone to show me evidence that they do anything except fill the air gap so that they pass NDI and give the technician a warm fuzzy feeling that he has repaired the defect. I have hundreds of examples including some where this OEM repair method has resulted in in-flight failures of large structures.

You ask what Fsu can be achieved by an adhesive bond. The answer is as much as the metal can sustain up to a thickness of 0.15 in for most high strength aluminium alloys. Firstly, understand that lap shear strength is a meaningless parameter which has absoultely nothing to do with bond strength, unless your bond is between 0.062 2024-T3 aluminium and you have used a stupid overlap length of 0.5 inches. Change the material, the overlap length or the thickness of the adherends and you get a different value.

It is actually possible to calculate the load capacity of the bond (the strength of the bond if the adherend failure is ignored) using equations derived by John Hart-Smith in the early 1970's. These equations deal with dissimilar materials, different adherend thicknesses and even thermal stresses. If that load capacity is greater than the unnotched strength of the adherends, then the adherends will fail first provided the overlap length is adequate. It will be physically impossible to exceed the strength of the adhesive because the adherends will fail first.

Next is the processing. You are correct that this is important and there are three factors; the surface preparation method, the temperature measurement and control processes and contamination control. Contamination is well known as a source of bond failure and simple methods can significantly reduce the risks. Temperature measurement and control for hot-bonding is currently a disaster waiting to happen. Almost every SRM directs the use of a single heater blanket irrespective of heat sinks and heat loss paths. They also specify a set array of thermocouples (four thermocouples arranged at 90 degrees apart). These directions result in either overheating of the structure or undercure of the adhesive and subsequent interfacial failure. I am aware of a 767 in the Pacific with a trailing edge flap corner repair performed by an authorised repair station that has fallen off the aircraft at least four times. My bet is that the adhesive has been heated too slowly causing the polymers to crosslink before the adhesive has flowed sufficiently to wet the surface. The mechanism is the same as using adhesive which is out of life. The failure is at the interface.

By far the most critical is the surface preparation method. Here is the real problem. Do you know that current certification methods for aircraft structures requires demonstration of static strength and fatigue resistance, but current regulations DO NOT require demonstration of long term bond durability. The only requirement is that bonding processes must produce a "sound" structure. What is a sound structure? If it passes NDI is that sound? If it passes static strength and fatigue testing is that sound? The anwer is a definite NO!

I could make a bonded structure which passes static strength and fatigiue tests in the short term, but will fail in long term service. The mechanism invoilved is that the chemical bonds formed at the time the adhesive is cured are sufficient to enable static strength and fatigue performance. However, in service these bonds degrade usually by hydration of the metal oxides. To enable the oxide surface to hydrate the chemical bonds at the interface dissociate leading to interfacial disbonding. The secret to a successful bond is to treat the surface at the time of bonding with chemicals which prevent hydration.

Now because the FARs, JARs etc. do not mandate testing to demonstrate resistance to hydration, we continue to see interfacial failures and loads well below even limit load, let alone ultimate load. Even worse, the bonding methods contained in SRMs are among the worst offenders. The only processes I would trust are phosphoric acid anodising (below 85F or 29C) the RAAF grit blast and silane process and Boeing's sol-gel process. Pasajel, alodine and many other proprietary processes are useless.

All of this is contained in the FAA publication DOT/FAA/AR – TN06/07, Apr 2007 available throught eh FAA Tech Center. Unfortunately because of homeland security, people outside the US (inluding myself as author) can not access the docoment without a request by email. I can send a draft copy to anyone on request.

Regards

blakmax.

Now MOD how about a new thread on adhesive bonding technology?

[cwatters]

Thanks for 1st class post Blakmax.

[muduckace]

Great post Blakmax,

We are entering a new era of common usage of composite materials, my greatest fear is the numerous environmental factors that influence our ability to inspect and repair composite structures with a narrow margine of error that the system may not proactivly support given the current airline/business global culture.

[blakmax]

Thanks for the supporting comments cwatters and muduckace. My main concern is the certification aspects for adhesive bonded structures and repairs. I am really concerned that the current FARs do not prevent a common (the most common) cause of failure of adhesive bonded structures and yet we see more and more structural bonds being incorporated in primary and flight critical aircraft structures. Helicopter main rotor blades are almost all exclusively adhesive bonded and they are certainly flight critical.

Maybe it is time to start a new thread. This discussion is way off the original subject, but thanks for the feedback.

Regards

blakmax

[rottenray]

Maybe we need to start a new thread because this is getting off the subject... other proprietary processes are useless.

Whole post here: Bonded Repairs (http://www.pprune.org/rumours-news/381184-southwest-737-lands-yeager-airport-after-hole-fuselage-6.html#post5073505)

Thanks for a most cogent explanation and one of the best contributions to general knowledge I've ever read, here or anywhere else.

Anyone who has tried to patch a hull breach in a jetski or similar composite hull can attest to the fact that you can do the same exact technique on two different parts of the hull and achieve 2 different levels of success, because of the different levels of demand on the patches and the difference in what each part of the hull was exposed to in normal use.

We've had centuries of experience with sheet metal but very little by comparison dealing with composite layups.

It's going to be very interesting to see how Boeing's 7L7 fuse barrels behave initially, and how some of ABI's composite panels - in service for years - look after a couple decades of commercial (don't give a s**t) use.

One can expect "learning situations" as we gain the same level of intuitive knowledge for composites that we already have for sheet metal.

And kudos to all the other contributors here - this is one of the least acrimonious threads I've ever read on pprune, and perhaps one of the most important.


...

[Volume]

We've had centuries of experience with sheet metal but very little by comparison dealing with composite layups.We have about half a century of experience with repairing composite gliders. It all started even before the US manufacturers started to mount jet engines on their passenger aircraft... We have repaired hundreds of broken wings, which would have been scrapped if they would have been made from metal! Just imagine repairing a metal wing spar broken of close to the wing root. For composite it often is possible to repair such damage, and it is indeed done on a regular basis. However, it needs a totally different level of skilled repairmen to perform this, and I agree, there are not too many of them around.

[blakmax]

Firstly thanks to rottenray for the delightful comments. After many years as a young angry man, I was once told by a very wise person that "you catch more flies with honey than you do with vinegar." That's why the responses are reasonably friendly, and I hope they will continue to be.

I noted Volume's comments We have about half a century of experience with repairing composite gliders. Volume, I bet that absolutely none of these were bolted repairs, so why do Boeing plan to use bolted repairs for the 787 composite structure?

You are absolutely correct about the higher skill levels for bonded composite repairs. The RAAF in Australia restructured their training in 1992 to actually teach how to perform adhesive bonding (rather than the "follow the cook book" approach) and since that time our major repair facility cut the repeat-repair rate from 43% in 1992 to almost zero, saving five man years per year of effort every year since then. Yet civil training still aims at the lowest common denominator and teach to an appallingly low standard. This is stupid. It does not take much more effort to train people to be proficient composite and bonding technicians. I personally have trained even electronics technicians to perform adhesive bonds and to do the task to the best standards.

Part of the problem with the civil system is that they use the term "composites" to encompass composite materials as well as adhesive bonding, yet they are two separate and distinct technologies. Just because a technician can lay-up composite repair patches does not mean he can prepare a metal surface to bond that repair. The blurring of the boundaries also means that FAA documents such as AC 20-107A treat the certification of adhesive bond the same as they treat the certification of composite structures. Why? The design methodologies, the failure mechanisms and testing methods are dramatically different. Composites don't fail at an interface, but adhesive bonds often do. The only similarity is that the materials are sticky before they are processed.

Consider this: Current certification of adhesive bonded structures IAW AC 20-107A involves thousands of tests at coupon, element, structural detail, sub-component and component level. If as in my previous positing, the joint was designed such that the metal (or composite structure) ALWAYS failed before the bond, then the only thing measured by thousands of tests would be the strength of the metal or composite, not the bond. So why do thousands of tests?

The approach based on designing such that the bond was never the weak element in the joint would save millions of dollars in certification costs for bonded structures. A simple test program to characterise key adhesive properties (together with a change in design methodology) would be all that was required. Further testing to demonstrate bond durability is essential, but current tests required by the FARs do not actually demonstrate bond durability.

So, if we characterise the adhesive, demonstrate that the bonding process actually produces durable bonds, use a design methodology that assures the adhesive is never the critical element, train the technicians how to perform correct bonding processes and that joint or repair will NEVER fail. NEVER. Certification costs could be dramatically reduced and reliability would dramatically increase. Am I out with the faries? No, because using this approach we have had three bond failures since 1992, and in every case, technician error (or to be more precise technician short cuts) have been found as the cause of those failures.

Now we really are off the track about the pressurisation failure, but what the heck? I suggested that the Moderator could pull me into line by moving the discussion to a seperate thread, but I've had no response, so lets keep the discussion going.

Regards

blakmax

[HarryMann]

.. and fractured it somewhere around the periphery :ugh:

Bliddy heck !

[WhyIsThereAir]

Apparently technicians are standing on the damaged area of the fuselage to access other areas for inspection.

If it doesn't say NO STEP and you need to stand there to maintain the aircraft, standing there doesn't seem to be an unreasonable thing to do. Maybe that is why there was that bonded panel on the original piece, to keep it from buckling and punching thru under the weight of shoes.

Of course, if one accepts that it is a step point, it probably affects what the structure should look like. So maybe this isn't a bonding or vibration fatigue failure, but instead failing to design it to be walked on?

[HarryMann]

Surely at those skin thicknesses and frame/stringer pitches the whole top of the fusleage is 'No Step' without writing it over the whole thing?
Not forgeting that 'No Step' for a 10 stoner in trainers being careful to step on rivet lines is a bit different than an 18 stoner in hob-nailed boots, sticking his boot in the middle of panels... so take the worse case and placard for saddles and planks or a cherry-picker.

[blakmax]

Guys

No matter how you package this with regard to the 10 stone weakling or the 20 stone average American inspector, the real problem is that the reinforcement bonded to the skin bay reinforced everywhere but the actual section transferring the load. One side of the cracked area has skin plus frame, the other side has skin plus factory-bonded doubler. The gap in between has skin only. Now Winnie the Pooh (the bear with very little brain) could work out that if there was a pressurisation-stress fatigue or over-weight inspector overload problem anywhere, it would happen there. (Even Homer would say DUH!)

The real question is, where are the similar "reinforced" areas on the aircraft where the local stiffness and thickness changes are so significant?

Was this a BIP? (Boeing Induced Problem)

Regards

blakmax

[WhyIsThereAir]

It occurred to me to wonder if this was a cabin overpressure 'pop top' that was designed to break out in the case of a severe overpressure. There is little doubt that the skin separated at the point one would expect it to separate.

[kenhughes]

According to this article: Southwest fuselage hole prompts Boeing 737 directive (http://www.flightglobal.com/articles/2009/09/14/332291/southwest-fuselage-hole-prompts-boeing-737-directive.html)

The FAA will issue an AD tomorrow (Tuesday, Sept 14), "proposing that operators of approximately 135 US-registered Boeing 737-300, -400 and -500 aircraft begin performing external non-destructive inspections of a certain area of the fuselage skin for evidence of fatigue cracks every 500 flights".

However, "operators who have installed an external doubler in the area, as specified in a previous Boeing service bulletin, will not have to perform repetitive inspections after an initial check, providing the repair meets certain other criteria spelled out in the proposed AD".

[nonsense]

It's a little frustrating to read an old thread like this and not find any answers; a bit like a library book with the last few pages torn out!
So here are the last couple of pages:
https://www.ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20090714X83900&ntsbno=DCA09FA065&akey=1
https://en.wikipedia.org/wiki/Southwest_Airlines_Flight_2294

[lomapaseo]

It's a little frustrating to read an old thread like this and not find any answers; a bit like a library book with the last few pages torn out!
So here are the last couple of pages:
https://www.ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20090714X83900&ntsbno=DCA09FA065&akey=1
https://en.wikipedia.org/wiki/Southwest_Airlines_Flight_2294

More importantly what is the lesson learned for other operators/manufacturers?