BOEING B737 & B757 (Toutes Générations, toutes Variantes)

Jeannot a écrit:Nouveau problème de décompression lié à un "trou" dans la cralingue d'un 737 de SouthWest

Flight Lands After ‘Fuselage Rupture’

PHOENIX (AP) — One passenger said it was a "real quick blast, like a gun." Another called it "pandemonium." Still another described watching a flight attendant and another passenger pass out, their heads striking the seats in front of them as they lost consciousness.

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A photo provided by a passenger of a Southwest Airlines plane that landed Friday after its cabin decompressed

Federal officials said it was a "fuselage rupture" — a large hole on the top of the Boeing 737 — that led to a loss of cabin pressure and a terrifying descent from 36,000 feet to an emergency landing at a military base in the Arizona desert.
No serious injuries were reported among the 118 aboard, according to Southwest Airlines, and the FBI said it was a "mechanical failure," not an act of terror or other foul play. The cause of the hole was not immediately known.
Passenger Brenda Reese said Flight 812 had just left Phoenix Sky Harbor International Airport for Sacramento, Calif., when a "gunshot-like sound" woke her up. She said oxygen masks dropped for passengers and flight attendants as the plane dove.
Ian Gregor, a Federal Aviation Administration spokesman in Los Angeles, said the pilot "made a rapid, controlled descent from 36,000 feet to 11,000 feet altitude."
[Vous devez être inscrit et connecté pour voir ce lien], who was seated one row from the rupture, said it took about four noisy minutes for the plane to dip to less than 10,000 feet, which made him "lightheaded."
During the rapid descent, "people were dropping," said Christine Ziegler, a 44-year-old project manager from Sacramento who watched as a crew member and a fellow passenger nearby faint, hitting their heads on the seats in front of them.
Larry Downey, who was seated directly below the hole when it opened, told Phoenix TV station KPNX that "it was pandemonium."
"You could look out and see blue sky," he said.
Joshua Hardwicke said he was awakened by a "sound like you shook up a pop can and dropped on the ground. It was like a firecracker."
The 24-year-old motorcycle technician was seated seven rows from the hole, which Reese described as "at the top of the plane, right up above where you store your luggage."
"The panel's not completely off," she told The Associated Press. "It's like ripped down, but you can see completely outside... When you look up through the panel, you can see the sky."
Cellphone photographs provided by Reese showed a panel hanging open in a section above the plane's middle aisle, with a hole of about six feet long. Nelson compared the noise to a gun, "a real quick blast," and said when the hole "first blew out, you could tell there was an oxygen deficiency."
The plane landed at a military base in Yuma without any injuries reported, except for a flight attendant who was slightly injured, according to the airline. Reese said the crewmember fell and injured his nose, and that some people passed out "because they weren't getting the oxygen."
The [Vous devez être inscrit et connecté pour voir ce lien] said an "in-flight fuselage rupture" led to the drop in cabin pressure aboard the 15-year-old plane. A similar incident on a Southwest plane to Baltimore in July 2009 also forced an emergency landing when a foot-long hole opened in the cabin.
Four months earlier, the Dallas-based airline had agreed to pay $7.5 million to settle charges that it operated planes that had missed required safety inspections for cracks in the fuselage. The airline, which flies Boeing 737s, inspected nearly 200 of its planes back then, found no cracks and put them back in the sky.
Julie O'Donnell, an aviation safety spokeswoman for Seattle-based Boeing Commercial Airplanes, confirmed "a hole in the fuselage and a depressurization event" in the latest incident but declined to speculate on what caused it.
Reese said there was "no real panic" among the passengers, who applauded the pilot after he emerged from the cockpit following the emergency landing at Yuma Marine Corps Air Station/International Airport, some 150 miles southwest of Phoenix and about 40 minutes after takeoff from Sky Harbor.
"It was unreal. Everybody was like they were high school chums," Ziegler said, describing a scene in which passengers comforted and hugged each other after the plane was on the ground. Southwest sent another airliner to take them to Sacramento later Friday.
"I fly a lot. This is the first time I ever had something like this happen," said Reese, a 37-year-old single mother of three who is vice president for a clinical research organization. "I just want to get home and hold my kids."
Gregor said an FAA inspector from Phoenix was en route to Yuma. The NTSB said it also was sending a crew to Yuma.
Holes in aircrafts can be caused by metal fatigue or lightning. The [Vous devez être inscrit et connecté pour voir ce lien] said the weather was clear from the Phoenix area to the California border on Friday afternoon.
In 1988, cracks caused part of the roof of an Aloha Airlines Boeing 737 to peel open while the jet flew from Hilo to Honolulu. A flight attendant was sucked out of the plane and plunged to her death, and dozens of passengers were injured.

[Vous devez être inscrit et connecté pour voir ce lien]

US low-cost carrier Southwest Airlines is to ground over 80 [Vous devez être inscrit et connecté pour voir ce lien] aircraft pending immediate inspections after a fuselage hole was discovered in a jet that depressurised on a service to California.

Southwest says that it has "decided to keep a subset of its [Vous devez être inscrit et connecté pour voir ce lien] 737 fleet out of the flying schedule" to commence an "aggressive inspection effort".

It says 81 aircraft are affected by the checks and that these will be examined over the next few days. The jets are covered by US FAA airworthiness directives detailing checks for skin fatigue.

Southwest has taken the action after one of its 737-300s, operating flight WN812 between Phoenix and Sacramento, diverted to Yuma yesterday after a loss of cabin pressure and deployment of oxygen masks.
"Upon landing safely in Yuma the flight crew discovered a hole in the top of the aircraft," says the carrier, adding that it was located about mid-cabin. It has not indicated the size of the rupture.

One of the 118 passengers and one of the five cabin crew members were treated for minor injuries.
The aircraft involved, identified by the US National Transportation Safety Board as bearing registration N632SW, carries serial number 27707 and is a 15-year old airframe.

"We have launched personnel to Yuma to begin the investigation process with the NTSB, FAA and appropriate parties to determine the cause of the depressurisation," says Southwest chief operating officer Mike Van de Ven.
It says it is working with Boeing on the details of the inspections for the aircraft.

Southwest suffered a similar incident two years ago when a Nashville-Baltimore service - also operated by a 737-300 - diverted to Yeager after being holed in its upper fuselage in July 2009.
Investigation attributed the hole to fatigue cracks and the incident prompted the FAA to mandate a Boeing service bulletin covering fatigue checks on certain older-variant 737s.

Sevrien a écrit: Boeing commence à avoir un historique d'incidents de "depressurisation", et de "trous" et points faibles dans le fuselage.

Aviation regulators will order tougher inspections of hundreds of Boeing 757 planes worldwide, after a recent in-flight incident that left a hole in the fuselage of an American Airlines plane, The Wall Street Journal reported on Friday.

According to the newspaper, the Federal Aviation Administration has drafted enhanced inspection mandates after a in-flight incident that occurred on October 26 when an American plane was cruising at 31,000 feet en route from Miami to Boston.

A Boeing spokeswoman told The Wall Street Journal that the company has already issued a bulletin urging carriers to inspect the upper forward skin on certain 757s to detect potential cracks.

The American jet, a Boeing 757-200, made an emergency landing at [Vous devez être inscrit et connecté pour voir ce lien] after experiencing a rapid decompression, not long after the aircraft had departed Miami en route to [Vous devez être inscrit et connecté pour voir ce lien].
AA flight 1640 was carrying 154 passengers and 6 crew. The crew donned their oxygen masks and initiated an emergency descent as the passenger oxygen masks were deployed.
A post flight inspection revealed a hole of about 1 foot by 2 feet (33 by 66cm) just above the “A” of the American Airlines Logo.

According to the Journal, the same month cracks were found in the fuselage of a United Airlines Boeing 757. Another American 757 was undergoing repairs in Los Angeles this week due to fuselage cracks.

US low-cost carrier Southwest Airlines is to ground over 80 [Vous devez être inscrit et connecté pour voir ce lien] aircraft pending immediate inspections after a fuselage hole was discovered in a jet that depressurised on a service to California.

Southwest says that it has "decided to keep a subset of its [Vous devez être inscrit et connecté pour voir ce lien] 737 fleet out of the flying schedule" to commence an "aggressive inspection effort".

It says 81 aircraft are affected by the checks and that these will be examined over the next few days.

The jets are covered by US FAA airworthiness directives detailing checks for skin fatigue.

Southwest has taken the action after one of its 737-300s, operating flight WN812 between Phoenix and Sacramento, diverted to Yuma yesterday after a loss of cabin pressure and deployment of oxygen masks.

"Upon landing safely in Yuma the flight crew discovered a hole in the top of the aircraft," says the carrier, adding that it was located about mid-cabin.

It has not indicated the size of the rupture.

One of the 118 passengers and one of the five cabin crew members were treated for minor injuries.

The aircraft involved, identified by the US National Transportation Safety Board as bearing registration N632SW, carries serial number 27707 and is a 15-year old airframe.

"We have launched personnel to Yuma to begin the investigation process with the NTSB, FAA and appropriate parties to determine the cause of the depressurisation," says Southwest chief operating officer Mike Van de Ven.

It says it is working with Boeing on the details of the inspections for the aircraft.

Southwest suffered a similar incident two years ago when a Nashville-Baltimore service - also operated by a 737-300 - diverted to Yeager after being holed in its upper fuselage in July 2009.

Investigation attributed the hole to fatigue cracks and the incident prompted the FAA to mandate
a Boeing service bulletin covering fatigue checks on certain older-variant 737s.

US safety inspectors have found evidence of "widespread cracking" and fatigue on the fuselage of a Southwest Airlines Boeing 737 that made an emergency landing in Arizona with a hole in the cabin, a government official said on Sunday.

"Was the aircraft well maintained and should it have been maintained better? That is exactly why we are here, to look at why this problem occurred," National Transportation Safety Board Member Robert Sumwalt said at a press conference in Yuma, Arizona.

As a result of the incident, Southwest has grounded part of its fleet for inspections.
The airline cancelled 300 flights on Saturday and said it expects to cancel another 300 flights on Sunday as the investigation continues into what caused the five-foot (1.5 metre) long, one-foot (35 cm) wide tear to develop during Southwest Flight 812 on Friday.

The flight from Phoenix to Sacramento landed at a military base in Yuma, Arizona, after the hole appeared suddenly at about mid-cabin.
The cancellations are likely to continue for the next few days, Southwest Airlines spokeswoman Whitney Eichinger said.
She said the airline would provide no additional comment due to the active investigation.

Sumwalt said he did not know of any additional problems with Southwest's Boeing 737 fleet.
Airline mechanics soon will saw out the portion of the plane skin that fractured during Flight 812, and it will be shipped overnight to Washington for further inspection, Sumwalt said.
It will take six to eight hours to remove the piece, which is expected to be about eight or nine feet (2.4 to 2.7 metres) long and two feet (0.7 metre) wide and weigh about three to four pounds (1.36 to 1.81 kg).
Sumwalt said there was evidence of what is known as "multi-site damage."

"We did find evidence of widespread cracking across this entire fracture surface," he said.
Sumwalt said the tear occurred in a concealed part of the plane and could not have been detected by the naked eye. He said the plane was most recently disassembled for heavy maintenance in March 2010, which would have been the last time such a fracture could have been detected.

Recorders from Flight 812 arrived at NTSB's headquarters on Saturday night, and they indicated that the decompression occurred approximately 18-1/2 minutes after takeoff, Sumwalt said.
The flight crew donned oxygen masks and declared an emergency.
The plane descended from its cruising altitude of 36,000 feet (10,970 metres) to 11,000 feet (3,350 metres) in approximately 4-1/2 minutes, Sumwalt said.
An inspection of the oxygen generators that supply oxygen to passengers indicated that the generators all had been activated, Sumwalt said.
A total of 931 Boeing 737-300s are operated by all airlines worldwide, with 288 of them in the United States, the Federal Aviation Administration said earlier.

(Reuters)

PHOENIX -- Federal investigators said inspectors have found subsurface cracks in three more Southwest Airlines planes.

Similar cracks are suspected of triggering a fuselage rupture that forced a Boeing 737-300 to make an emergency landing in Yuma, Ariz. The 15-year-old jet in the [Vous devez être inscrit et connecté pour voir ce lien] incident had about 39,000 takeoff and landing cycles.

The airline had said earlier Sunday that it found such cracks in two of their planes. A National Transportation Safety Board member said a third plane was discovered to have the cracks as well.

Board member Robert Sumwalt says Boeing is developing a "service bulletin" strongly suggesting immediate checks on all similar models with comparable [Vous devez être inscrit et connecté pour voir ce lien] time and age.

The cracks found in the three planes developed in two lines of riveted joints that run the length of the aircraft.

Southwest Airlines spokeswoman Whitney Eichinger said the airline canceled 300 flights on Sunday as the airline inspected 79 of its Boeing 737 aircraft in the aftermath of an emergency landing.

The move follows 300 cancellations by the airline on Saturday.

Ann Freeman drove up from Marana to pick up her grandson. She said news has her a bit on edge.

"I’m a little worried because it's his first time to fly alone. He's only 11," said Freeman.

Federal Aviation Administration officials said Southwest flight 812 was forced to make an emergency landing in Yuma Friday after a hole was ripped in the roof of the cabin.

"And all of a sudden there is a loud bang. And the masks dropped and it's really, really windy," said flight 812 passenger Shawana Melvin Redden.

Pilots safely landed the plane without anyone getting hurt. Hours later Southwest officials made the decision to ground 79 of its Boeing 737 aircraft, so that engineers could inspect the planes for what they call skin fatigue.

Most people we talked to didn't seem to mind the wait.

"Better safe than not," said Southwest passenger Mike Pimper.

"When something like that happens I don't know what the cause was but they have to be careful as they can be and if that causes a little inconvenience so be it," said Freeman.

Southwest has not announced if more flights will be effected Monday.

The waiting continues at Sky Harbor International Airport after Southwest officials canceled hundreds of flights for the second day in a row.

"It seems like all their flights right now are by the hour," Southwest passenger JJ Lally said. "So we'll see how it goes."

Lally is hoping his flight to Chicago won't joins the dozen or so canceled from Phoenix on Sunday.

SEVRIEN a écrit:
Et ici, ... on ne peut pas écarter facilement un problème de "fundamental flaw", même si cela ne concerne qu'un "lot" ou qu'une série importante "production run / batch"), que ce soit dans la conception, "design", structure, et / ou le(s) matériau(x) !

Boeing: 737 cracks showed up much sooner than anticipated

Boeing engineers knew about potential cracking in the area of older 737 aircraft where a hole opened on a Southwest jet in flight Friday, but thought problems wouldn’t show up until much later, a company official said Tuesday.
“We did anticipate that there would be a need to inspect the airplane at some point in time,” Paul Richter, Boeing chief project engineer for out-of-production aircraft, said in a conference call with reporters.
“However, all of the analysis and testing that supported that activity convinced us that we would not have an issue with this lap joint lower row until much much later in the life of the airplane,” he added. “Our plan previous to this event was to recommend inspections starting at 60,000 cycles, which we felt was a very conservative number, and obviously none of the airplanes of this configuration are anywhere close to that at this point in time.”

The Southwest 737-300 that developed a 5-foot-long hole soon after takeoff Friday from Phoenix had about 40,000 cycles (takeoffs and landings). A lap joint is where two pieces of the fuselage overlap and are riveted together.
Boeing improved the lap joints on these aircraft in response to problems on previous models that resulted in the company calling for replacing the joints on those older aircraft at 50,000 cycles, Richter said. That requirement applies to more than 2,000 older 737s.
Boeing’s current [Vous devez être inscrit et connecté pour voir ce lien] production models, the 747-600, -700, -800 and -900, have several differences in the design of the lap joints, most notably improvements that significantly reduce bending that contributes to fatigue cracks, Richter said. “We remain completely confident that there is no lower-row cracking issue with the lap joints on the NG design.”
Late Monday, Boeing issued a service bulletin calling on airlines to inspect Boeing 737-300s, -400s and -500s with more than 35,000 cycles within five days and with 30,000 to 35,0000 cycles within 20 days, Richter said. He said the inspections take about eight hours per aircraft.
The inspections cover about a 50-foot section of lap joints on both sides of the crown of the aircraft and use eddy-current devices, which “can look through layers of aluminum for disruptions in the magnetic field, which are signatures for cracks that are in the base metal below,” Richter said. “Our inspection techniques today are quite sensitive at finding very short cracks that are at such a length that there’s really no risk of multiple cracks connecting with each other, which is what apparently happened with this event airplane.”
The bulletin mirrors [Vous devez être inscrit et connecté pour voir ce lien] and applies to about 175 aircraft built between 1993 and 2000. There are about 395 more of these models that have not yet reached 30,000 cycles, Richter said.
The trigger threshold of 30,000 cycles is a “conservative estimate of when cracks might be detectable in this location,” Richter said.
The FAA has called for repeat inspections after 500 cycles as a precautionary step. Richter said Boeing engineers would come up with a recommendation on what inspection interval would be needed as they analyze the incident.
Southwest Airlines completed inspecting all but two of its 79 affected 737s as of Tuesday morning, reporting: “Minor subsurface cracking was found in five aircraft that will remain out of service until Boeing recommends appropriate repairs and those repairs have been completed.”
Boeing has given Southwest repair guidance on three aircraft, calling for replacement of an 18-inch length of lap joint to ensure removal of any undetected cracks, Richter said, adding that the repair should take eight to 16 hours. Boeing will give repair guidance on a case-by-case basis for now and include repair information in a future service bulletin update, he said.

vonrichthoffen a écrit:

SEVRIEN a écrit:
Et ici, ... on ne peut pas écarter facilement un problème de "fundamental flaw", même si cela ne concerne qu'un "lot" ou qu'une série importante "production run / batch"), que ce soit dans la conception, "design", structure, et / ou le(s) matériau(x) !

Dans tous les niveaux de l'aviation, il y a des types d'avions qui révèlent une faiblesse chronique largement après avoir été certifiés, parfois au bout de deux ou trois décénies de bons et loyaux services. Il est difficile de parler de défaut fondamental dans ces cas là.
Il y a un facteur humain ici, qui s'appuie sur la bonne réputation de l'appareil, son côté increvable, et qui aura pu alimenter non pas une négligence contributive, mais faire baisser le niveau de vigilance des opérateurs.
Ces avions concernés doivent tous avoir derrière eux une vie bien remplie avec un nombre élevé de cycles.

• "le DC-9 avait été conçu pour décoller & atterrir, ... décoller & atterrir, ..... décoller & atterrir, .... décoller & atterrir, ... et, encore, ... décoller & atterrir, .... et décoller & atterrir, ... sans jamais se fatiguer ;
  
• "le B737 est un avion fabuleux, qui sera amélioré pendant longtemps, ... mais il ne sera jamais aussi robuste que le DC-9, et ses évolutions ; c'est une impossibilité physique ;
  
• "même chose pour le B757 ;
  
• 'il y a un point faible fondamental qui se manifeste sur certains modèles, ou lots ("production runs") ;
  
• "toutes proportions gardées, car le B757 est plus long que les B737, et on ne sait pas pourquoi, mais il ye des "cracks" / 'petites fissures' .... "under the skin", qui se forment, au même endroit relatif, dans la partie latérale supérieur du fuselage "starboard" ('tribord') ;
  
• "si l'on ne les traite pas, et les surveille pas ensuite, cela finit par faire des trous dans le fuselage ("outer skin") ;
  
• 
  
• "on dirait une 'fatique' du métal, .... mais on ne comprend pas pourquoi ; ou on n'a pas assez bien cherché . mais ces Boeing ne peuvent pas être mal-traités, comme nos bons vieux appareils DC-9 " !
  

Au plaisir de vous relire, car j'ai fait un peu de provocation (je l'avoue) contre les habitués du coin du CVomptoir du Café de la Gare !

Nils a écrit:Bonjour, merci

Juste une remarque :

Constat de demande, calculée sur les valeurs actuelles et il y a un an

A / Boeing 757-200 en ACMI + F ( Wetlease ) : $5,500US/BH
( guaranteed 250 HRS/MO ).

B / Boeing 737-300 en ACMI + F ( Wetlease ) : $2,000US/BH
( guaranteed 250 HRS/MO ).

Il y a un an

A : $5,750US/BH ( 250 HRS/MO )

B : $3,250US/BH ( 250 HRS/MO )

Boeing issues service bulletin for premature 737 Classic lap-joint cracking

[Vous devez être inscrit et connecté pour voir ce lien] has issued a service bulletin that covers the operators of approximately 175 737-300/400/500s requiring a inspections on the aircraft fuselage structure to begin within five days for aircraft with more than 35,000 cycles, and 20 days for aircraft with 30,000 to 34,999 cycles, with the US Federal Aviation Administration requiring repeated examination every 500 cycles.
The requirement comes in the wake of the 1 April fuselage rupture aboard a Southwest Airlines 737-300, that developed lap-joint cracks far earlier in its service life than anticipated, says Boeing's 737 Classic chief project engineer, Paul Richter.
The US airframer issued the service bulletin late on 4 April disclosing the requirement to conduct dial frequency Eddy-current inspections on the lower row of fasteners in the fuselage lap-joint, along the left and right-hand side of the crown of the aircraft at stringer four between Station 360 - just aft of the fwd passenger door - and Station 908 - a few frames ahead of the rear passenger door, covering roughly 15.2m (50ft) and almost the entire length of the passenger cabin.
The service bulletin applies only to 737 Classic aircraft with line numbers 2553 and 3132 inclusive, which were delivered from 1993 until the end of the Classic's production run in 2000. Paired with the 30,000 cycle requirement, a total of 175 aircraft worldwide meet this criteria, with 80 operating within the US, almost entirely for Southwest Airlines. The majority of the balance are operating in Europe and Asia, says Boeing.
What distinguishes this tranche of 579 737s is a design modification that was intended to eliminate the requirement for a lap-joint modification programme already in effect for line numbers 292 through 2552 inclusive, which were required above 50,000 cycles.
Richter, who serves as chief project engineer for Boeing's out of production aircraft, including the 737 Classic, says Boeing had anticipated some level of structural cracking in the area in question, though it had been expected to occur around 60,000 cycles, far later than the 39,000 cycles of the aircraft involved in the 1 April incident.
The design change increased the spacing of the tear strap frames from 10in to 20in inside the fuselage, which are intended to prevent fuselage damage from propagating across structural frames in the event of a failure. Ultimately the updated design on the newer 737 Classics was intended to increase the fatigue life of the lower row of the lap-joint.

[Vous devez être inscrit et connecté pour voir ce lien]

The service bulletin "currently does not have a repetitive inspections listed in it," says Richter, but the FAA will mandate a 500 cycle repeat interval as part of its emergency airworthiness directive as a precautionary measure. Richter adds that requirement will be reviewed "through the course of our analysis for adjustments as required down the road".
Richter says 500 cycles is a "rare interval to impose, it is quite frequent and has been used before with similar concerns." He adds Boeing and the NTSB have suggested a precautionary and conservative interval until the root cause of the 1 April fuselage structural failure is established.
Richter adds examinations, which will look for disruptions magnetic field, indicating signatures for cracks in the base metal, will take roughly 8h per airframe with two mechanics in a maintenance environment, with another 8-16h to repair any cracks.
Following the 1 April incident and emergency landing Yuma, Southwest removed 79 additional 737-300s from service and conducted Eddy-current structural inspections on the aircraft. Separately from the event aircraft, a total of five additional aircraft have been removed from service after cracks in the lap-joints were discovered.
Richter says Boeing has not yet issued guidance to the airlines on how to repair the lap-joints if they are found to be cracking, adding that later revisions of the service bulletin will address this, along with any necessary preventive measures.
Richer says Boeing is "completely confident" that no such lower row cracking issue exists with the lap-joints on any of the 737 Next Generation models that have been in service since 1997 .

Jeannot a écrit:Les fissures sur les 737s étaient prévues mais sont arrivées plus tôt que prévu (40.000 cycles au lieu de 60.000)

Boeing: 737 cracks showed up much sooner than anticipated

Boeing engineers knew about potential cracking in the area of older 737 aircraft where a hole opened on a Southwest jet in flight Friday, but thought problems wouldn’t show up until much later, a company official said Tuesday.
“We did anticipate that there would be a need to inspect the airplane at some point in time,” Paul Richter, Boeing chief project engineer for out-of-production aircraft, said in a conference call with reporters..........

“However, all of the analysis and testing that supported that activity convinced us that we would not have an issue with this lap joint lower row until much much later in the life of the airplane,” he added. “Our plan previous to this event was to recommend inspections starting at 60,000 cycles, which we felt was a very conservative number, and obviously none of the airplanes of this configuration are anywhere close to that at this point in time.”

[Vous devez être inscrit et connecté pour voir ce lien] has issued a service bulletin that covers the operators of approximately 175 737-300/400/500s requiring a inspections on the aircraft fuselage structure to begin within five days for aircraft with more than 35,000 cycles, and 20 days for aircraft with 30,000 to 34,999 cycles, with the US Federal Aviation Administration requiring repeated examination every 500 cycles.

The requirement comes in the wake of the 1 April fuselage rupture aboard a Southwest Airlines 737-300, that developed lap-joint cracks far earlier in its service life than anticipated, says Boeing's 737 Classic chief project engineer, Paul Richter.

The US airframer issued the service bulletin late on 4 April disclosing the requirement to conduct dial frequency Eddy-current inspections on the lower row of fasteners in the fuselage lap-joint, along the left and right-hand side of the crown of the aircraft at stringer four between Station 360 - just aft of the fwd passenger door - and Station 908 - a few frames ahead of the rear passenger door, covering roughly 15.2m (50ft) and almost the entire length of the passenger cabin.

The service bulletin applies only to 737 Classic aircraft with line numbers 2553 and 3132 inclusive, which were delivered from 1993 until the end of the Classic's production run in 2000. Paired with the 30,000 cycle requirement, a total of 175 aircraft worldwide meet this criteria, with 80 operating within the US, almost entirely for Southwest Airlines. The majority of the balance are operating in Europe and Asia, says Boeing.

What distinguishes this tranche of 579 737s is a design modification that was intended to eliminate the requirement for a lap-joint modification programme already in effect for line numbers 292 through 2552 inclusive, which were required above 50,000 cycles.

Richter, who serves as chief project engineer for Boeing's out of production aircraft, including the 737 Classic, says Boeing had anticipated some level of structural cracking in the area in question, though it had been expected to occur around 60,000 cycles, far later than the 39,000 cycles of the aircraft involved in the 1 April incident.
The design change increased the spacing of the tear strap frames from 10in to 20in inside the fuselage, which are intended to prevent fuselage damage from propagating across structural frames in the event of a failure. Ultimately the updated design on the newer 737 Classics was intended to increase the fatigue life of the lower row of the lap-joint.

The service bulletin "currently does not have a repetitive inspections listed in it," says Richter, but the FAA will mandate a 500 cycle repeat interval as part of its emergency airworthiness directive as a precautionary measure.

Richter adds that requirement will be reviewed "through the course of our analysis for adjustments as required down the road".
Richter says 500 cycles is a "rare interval to impose, it is quite frequent and has been used before with similar concerns." He adds Boeing and the NTSB have suggested a precautionary and conservative interval until the root cause of the 1 April fuselage structural failure is established.

Richter adds examnations, which will look for disruptions magnetic field, indicating signatures for cracks in the base metal, will take roughly 8h per airframe with two mechanics in a maintenance environment, with another 8-16h to repair any cracks.

Following the 1 April incident and emergency landing Yuma, Southwest removed 79 additional 737-300s from service and conducted Eddy-current structural inspections on the aircraft. Separately from the event aircraft, a total of five additional aircraft have been removed from service after cracks in the lap-joints were discovered.
Richter says Boeing has not yet issued guidance to the airlines on how to repair the lap-joints if they are found to be cracking, adding that later revisions of the service bulletin will address this, along with any necessary preventive measures.

Richer says Boeing is "completely confident" that no such lower row cracking issue exists with the lap-joints on any of the 737 Next Generation models that have been in service since 1997.

Le constructeur aéronautique américain Boeing a exonéré mardi Southwest Airlines et sa manière de gérer ses opérations d ans les fissures rencontrées par la compagnie aérienne américaine à bas prix sur plusieurs de ses 737. © 2011 AFP.

FAA mandates tough inspection regime for older Boeing 737s

Airlines that operate [Vous devez être inscrit et connecté pour voir ce lien] 737s face a rigorous new emergency inspection regime following the fuselage rupture of a Southwest Airlines 737-300 over Arizona on 1 April. The new requirement will see each aircraft undergo an 8h inspection every 500 cycles.
Within three days of the incident, Boeing issued a service bulletin covering the operators of about 175 737-300/400/500s, requiring inspections of fuselage structure to begin within five days for aircraft with more than 35,000 cycles, and within 20 days for those with 30,000 to 34,999 cycles.
Meanwhile, the Federal Aviation Administration has issued an emergency airworthiness directive requiring repeated examinations every 500 cycles.
The inspection will search for sub-surface cracks in the lap-joint of a subset of 737 Classic aircraft. The cracks have been found to develop far earlier in the aircraft's service life than had been anticipated, says Boeing's 737 Classic chief project engineer Paul Richter.
The US airframer issued the service bulletin late on 4 April, requiring dial frequency Eddy-current inspections on the lower row of fasteners in the fuselage lap-joint, along the left- and right-hand side of the crown of the aircraft at stringer four between Station 360 - just aft of the forward passenger door - and Station 908 - a few frames ahead of the rear passenger door. This covers about 15.2m (50ft) - almost the entire length of the passenger cabin.
The service bulletin applies only to 737 Classic aircraft with line numbers 2553 and 3132 inclusive, which were delivered between 1993 and the end of the Classic's production run in 2000. Paired with the 30,000-cycle requirement, a total of 175 aircraft worldwide meet this criterion, with 80 operated within the USA, almost exclusively by Southwest Airlines. Most of the others operate in Europe and Asia, says Boeing.
What distinguishes this tranche of 579 737s is a design modification that was intended to eliminate the requirement for a lap-joint modification programme already in effect for line numbers 292 to 2552 inclusive, which were required above 50,000 cycles.
Richter, who is chief project engineer for Boeing's out-of-production aircraft, including 737 Classics, says Boeing had anticipated some level of structural cracking in the relevant area, but had expected it to occur around 60,000 cycles, far later than the 39,871 cycles of the aircraft involved in the 1 April incident.
The design change increased the spacing of the tear strap frames from 250mm to 500mm (10in to 20in) inside the fuselage, which are intended to prevent fuselage damage from propagating across structural frames in the event of a failure. Ultimately, the updated design on the newer 737 Classics was intended to increase the fatigue life of the lower row of the lap-joint.
Richter says the service bulletin "currently does not have a repetitive inspections listed in it", but the FAA mandates a 500-cycle repeat interval under its emergency airworthiness directive as a precautionary measure. Richter says the requirement will be reviewed "through the course of our analysis for adjustments as required down the road".
He says 500 cycles is a "rare interval to impose - it is quite frequent and has been used before with similar concerns". He adds that Boeing and the National Transportation Safety Board have suggested a precautionary and conservative interval until the root cause of the 1 April structural failure is established.
The examinations, which will look for disruptions in a magnetic field, indicating signatures for cracks in the base metal, will take about 8h per airframe with two mechanics in a maintenance environment, taking a further 8-16h to repair any cracks, says Richter.
Following the 1 April incident and emergency landing at Yuma, Southwest removed 79 other 737-300s from service and conducted Eddy-current structural inspections on them. Apart from the event aircraft, five other 737s have been removed from service after cracks were discovered in the lap-joints.
Richter says Boeing has not yet issued guidance to airlines on how to repair the lap-joints if they are found to be cracking, pointing out that later revisions of the service bulletin will address this, along with any preventive measures.
He says Boeing is "completely confident" that no such lower-row cracking issue exists with the lap-joints on any 737 Next Generation models that have been in service since 1997.
In November 2010, the FAA required airframers to set life limits for almost 4,200 transport aircraft, giving them between 18 and 60 months to determine how many cycles or hours an aircraft type can safely accumulate.
FAA administrator Randy Babbit said in a 6 April US congressional testimony that the FAA would take a more active role in incorporating the Southwest accident into its rule-making. "I want to make absolutely certain that what we learn from this accident gets incorporated into our requirements for reviewing ageing aircraft," he said.
"I am asking my team to review our ageing aircraft programme to ensure we are asking the right questions and taking full advantage of all available data."

SEVRIEN a écrit:Bonsoir, cher vonrichthoffen, et merci !

vonrichthoffen a écrit:

SEVRIEN a écrit:
Et ici, ... on ne peut pas écarter facilement un problème de "fundamental flaw", même si cela ne concerne qu'un "lot" ou qu'une série importante "production run / batch"), que ce soit dans la conception, "design", structure, et / ou le(s) matériau(x) !

Dans tous les niveaux de l'aviation, il y a des types d'avions qui révèlent une faiblesse chronique largement après avoir été certifiés, parfois au bout de deux ou trois décennies de bons et loyaux services. Il est difficile de parler de défaut fondamental dans ces cas là.
Il y a un facteur humain ici, qui s'appuie sur la bonne réputation de l'appareil, son côté increvable, et qui aura pu alimenter non pas une négligence contributive, mais faire baisser le niveau de vigilance des opérateurs.
Ces avions concernés doivent tous avoir derrière eux une vie bien remplie avec un nombre élevé de cycles.

Je vous reçois "5 sur 5" !
Mais je base mes dires sur une vieille histoire d'un "As" de Douglas (avant MD). Il m'a dit que les Boeing B737 (-200 et les "classics", -300 / -400 / -500) n'arriveraient jamais à "hold a candle to le DC-9" (n'arriveraient jamais à rivaliser avec ou faire mieux que.... ).

Il m'a dit (à la fin des années 1970 / au début des années 1980) :

• "le DC-9 avait été conçu pour décoller & atterrir, ... décoller & atterrir, ..... décoller & atterrir, .... décoller & atterrir, ... et, encore, ... décoller & atterrir, .... et décoller & atterrir, ... sans jamais se fatiguer ;
  
• "le B737 est un avion fabuleux, qui sera amélioré pendant longtemps, ... mais il ne sera jamais aussi robuste que le DC-9, et ses évolutions ; c'est une impossibilité physique ;
  
• "même chose pour le B757 ;
  
• 'il y a un point faible fondamental qui se manifeste sur certains modèles, ou lots ("production runs") ;
  
• "toutes proportions gardées, car le B757 est plus long que les B737, et on ne sait pas pourquoi, mais il ye des "cracks" / 'petites fissures' .... "under the skin", qui se forment, au même endroit relatif, dans la partie latérale supérieur du fuselage "starboard" ('tribord') ;
  
• "si l'on ne les traite pas, et les surveille pas ensuite, cela finit par faire des trous dans le fuselage ("outer skin") ;
  
• 
  
• "on dirait une 'fatique' du métal, .... mais on ne comprend pas pourquoi ; ou on n'a pas assez bien cherché . mais ces Boeing ne peuvent pas être mal-traités, comme nos bons vieux appareils DC-9 " !
  

Il s'agit peut-être d'un vieux singe, bien sage, ... sagace, ... avec du vécu ! On dirait qu'il y a un peu de "what goes around comes around" !

Au plaisir de vous relire, car j'ai fait un peu de provocation (je l'avoue) contre les habitués du coin du CVomptoir du Café de la Gare !

Je ne cherche pas à "donner dans le paraître" comme ces Adeptes-là !

Mon interlocuteur a sa petite idée, du moins, sur un aspect important : variabilité dans la qualité des matériaux, incapables d'encaisser les vibrations, notamment acoustiques, qui ont eu des effets "reportés/ renvoyés" ailleurs (comme le "referred pain" dans les cas de blessures de rugby ou de football : on reçoit un coup sur la hanche, et on finit par avoir une douleur insupportable au dos ..... ; ce n'est qu'un illustration).

Réactions ?

Bonjour,

Questions de néophyte technique, sans malice :

Est-ce l'absence de moteurs sous voilure des DC 9 / MD 80 / B 717; avec wingbox adapté d'un fuselage cousin du DC-8 qui faisait ( fait encore ) cette solidité ?

Tout ensemble propulsif engendre des vibrations acoustiques, internes et externes. Tout renvoyer à l'arrière de la cellule protégerait l'ensemble fuselage - caisson central - voilure ?

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USA: des fissures sur un Boeing

Les enquêteurs du Bureau national de sécurité des Transports (NTSB) affirment avoir trouvé des fissures sur le fuselage du Boeing 737-300 de Southwest Airlines impliqué dans un incident début avril, ainsi des problèmes sur les rivets. Après examination au microscope du fuselage percé, le NTSB a trouvé des "fissures de fatigue" émanant d'au moins 42 des 58 rivets joignant deux pièces du fuselage, explique le Bureau dans une mise à jour de son enquête qui reste en cours.

Des signes de fissures ont également été retrouvés sur une partie du fuselage situé a proximité de la partie endommagée également collectée par les enquêteurs, autour de neuf rivets, précise le NTSB. Le Bureau a eu recours à une analyse aux rayons X pour étudier l'état des rivets restés intacts, qui a révélé des décalages entre la tige de plusieurs rivets et leurs trous correspondants. L'inspection a montré qu'à cet endroit les trous des pièces supérieure et inférieure du fuselage étaient en léger décalage les uns par rapport aux autres.

L'avion le plus vendu au monde

Début avril, un avion de Southwest Airlines dont la cabine était dépressurisée à cause d'un trou dans le toit avait dû effectuer un atterrissage d'urgence sur une base aérienne à Yuma (Arizona, Sud-Ouest). Southwest Airlines a trouvé des brèches dans cinq des soixante-dix-neuf Boeing 737 qu'elle a inspectés à la suite de l'incident. Le 737, un moyen-courrier biréacteur, est l'avion de ligne le plus vendu au monde. Il est très utilisé pour les vols régionaux ou nationaux.

Cracked 737 had misaligned rivet holes, NTSB reports

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Rivet holes on the Southwest Airlines Boeing 737 that [Vous devez être inscrit et connecté pour voir ce lien] did not line up properly, the National Transportation Board reported Monday.
We already knew that the 737-300 developed a 5-foot-long hole in a lap joint, where two pieces of the fuselage overlap and are riveted together.
Eddy current inspections around intact rivets forward of the hope “revealed crack indications at nine rivet holes in the lower rivet row of the lap joint,” the NTSB said. It said X-ray inspections then “revealed gaps between the shank portions of several rivets and the corresponding rivet holes for many rivets” and: “Upon removing selected rivets, the holes in the upper and lower skin were found to be slightly offset relative to each other and many of the holes on the lower skin were out of round.”
The NTSB noted that it found “fatigue cracks emanating from at least 42 of the 58 rivet holes connected by the fracture,” and that tests of the skin around the fracture “revealed that the aluminum skin material was consistent with the specified material. The skin was the specified thickness.”
Responding to the report, Boeing said:

Boeing will not speculate on what the NTSB’s initial findings may suggest about the root cause of the April 1 737-300 decompression event, which the investigation will determine in due course. Meanwhile, we remain fully engaged with the investigation and will work closely with both the NTSB and the FAA to ensure the highest level of safety continues for Boeing 737 Classics.
Boeing already has taken appropriate action by recommending lap-joint inspections to airlines worldwide on certain 737-300/400/500 airplanes, which the FAA also mandated as an airworthiness directive. To date, Boeing has confirmed that inspections are complete worldwide on nearly 80 percent of the 190 airplanes affected. A total of five airplanes have had inspection findings. In coordination with the NTSB, portions of the panels from those airplanes, which were delivered between 1994 and 1996, have been shipped to Boeing and we are conducting analyses to validate the initial inspection findings. No conclusions have been reached about root cause of the inspection findings, nor of any relationship to the April 1 event. Any attempt to draw conclusions on either would be premature and speculative.

The NTSB said reported that four 737s inspected after the incident were found to have “crack indications” at one rivet and one airplane had crack indications at two rivets.
“The lap joints from these areas of the subject airplanes have been removed will be fully documented as part of the NTSB investigation,” the agency said.
The agency said it is conducting additional inspections in these areas:

1. Removal of rivets and examination of rivet hole dimensions, rivet dimensions, and rivet hole alignment between upper and lower skins.
   
2. Detailed fractographic analysis of the skin fractures emanating from the rivet holes using optical and scanning electron microscopes.
   
3. Fatigue striation analysis using a scanning electron microscope of specific skin fractures to determine the rate of crack propagation.
   
4. Examination of additional portions a lap joints from the accident aircraft.
   

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A National Transportation Safety Board preliminary report released Monday on the April 1 incident raised new questions about the process for bonding fuselage skin and how wear and tear may affect certain older model Boeing 737-300 series aircraft.

Those planes have been a workhorse for decades in the global commercial fleet. Fatigue wear and cracks have long been a concern with older aircraft, including the so-called "classic" 737s made before the late 1990s.
Southwest Flight 812 made an emergency landing in Yuma, Arizona, with a five-foot roof tear over the left wing. The damaged area peeled back like the lid of a can. No one was hurt.
An examination by safety board investigators of the plane and a cutaway of the damaged skin showed microscopic cracks extending from at least 42 of 58 rivet holes connected to the rupture. Cracks also extended in an area forward of the hole.

A separate inspection of intact rivets showed imperfections in the location and size of several rivet holes, but the NTSB does not know if the problem is related to wear, manufacturing, or another cause.

Additionally, evidence of Southwest's blue livery paint was found inside a joint where the upper and lower fuselage skin meet and where microscopic cracks had been painted over.

Boeing said in a statement that it could not speculate on what the NTSB's preliminary findings might suggest about the root cause of the incident involving the 15-year-old jet.
Southwest said in a statement that the initial findings "were another step in this ongoing investigation" and pledged cooperation with investigators and regulators "in an effort to determine the cause of events."
There were nearly six hundred 737-300, 400, 500 series planes made between 1993-2000 with fuselage assembly at the company's Wichita, Kansas, facility.

Votre humble serviteur est content d'avoir donné un petit coup de gueule courtoissur cette affaire, dès l'origine ! Il est rafraîchissant que nous ayons eu des échanges sur cet aspect du topic, tandis que d'autres Forums n'ont fait que le "down-playing" / la 'minimisation' de ces incidents chez Southwest (sur les Boeing B737).

Boeing changed its 737 skin bonding techniques early on based on analysis and other factors including a similar incident in 1988 involving an Aloha Airlines 737-200. Boeing said it is unclear whether the change contributed to the Southwest incident.

Boeing said it was working closely with the NTSB and any attempt to draw conclusions about the Southwest incident "would be premature and speculative."

The Federal Aviation Administration, in consultation with Boeing after the Southwest rupture, ordered airlines to inspect 190 of those 737-300, -400 and -500s worldwide. Those planes, like the damaged Southwest jet, had a high number of takeoffs and landings. Expansion and contraction of the fuselage during flight can cause cracks.
Southwest grounded 79 of its jets before the FAA order that included its jets.

Boeing said inspections were completed worldwide on nearly 80 percent of the planes affected with cracks showing up on four -- all from Southwest. Southwest, which has an all-737 fleet, said it has since repaired those planes and put them back in service.
The jet with the ruptured skin remains sidelined, the company said.
FAA records show a series of directives over the years aimed at preventing and detecting cracks in the 737-300 family.

(Reuters)