Southwest Air’s second 737 decompression

Southwest Airlines suffered a second in-flight decompression of a Boeing 737-300 yesterday. This is the second–the first was in July 2009.

Both airplanes were 15-year old 737-300s and the failure on both airplanes were in the aft fuselage. The 2009 incident involved a hole in front of the vertical fin about one foot in size. Friday’s incident was bigger, about three feet, further forward and on the left size but aft of the wing.

Southwest grounded 79 737-300s for inspection, all about 15 years old. The company doesn’t have word how long the inspections will take; about 300 flights will be canceled today.

That both airplanes involved were 15 years old and areas of the plane involved were similar gives cause for concern.

According to Flight Global, the 2009 incident was due to fatigue cracking in the production process.

Southwest told us today that the aircraft now grounded for inspection were identified by Boeing and Southwest:

“In consultation with Boeing, we identified the 79 aircraft in our fleet that require inspections to address the potential for an incident similar to what occurred with Flight 812. It’s factual that they all are in the 15 year range,” Southwest said in an email to Leeham News.

Flight Global reported that the 2009 aircraft had about 42,500 cycles and 50,500 hours at the time of the incident. Friday’s airplane had 48,722 flight hours, according to the Internet, and 39,781 cycles, according to Southwest.

Boeing, in a statement we received in our role as aerospace analyst for KIRO TV News (Seattle), said it is too soon to make any connection between the 2009 and Friday incidents, pending the investigation.

Flightaware has Southwest’s descent profile. The pilot wasted no time in coming down to breathable air.

Here is piece we did for KIRO TV.

14 Comments on “Southwest Air’s second 737 decompression

  1. Hmmm- built around 1995 ? About the time they started having production problems ? And the photo shown had winglets- which were not really used/ installed on SW till 2002 – 2005 unless by refit.

    fatigue cracking in production process ?? overstressed fasteners/rivets ?? or oversized holes. ??

    Be interesting to read fAA report

  2. In a way, it was very “lucky”, that the “crack” on the SW 737-300 was three or more feet long and
    several inches wide, along the length of the fuselage and across several fuselage frames, allowing enough cabin air to escape in a very short time period, before causing much more damage!
    Had the crack gone across the fuselage, as it did on the Hawiian 737-200 in the 70s
    I believe it was, this would either have been another “flying convertible” incident, or such a
    something far worse!

    However, there is NO excuse whatsoever, for a SECOND 737-300, or even a first with only
    50,000 flight hours, to have experienced such an near fatal structural failure at SW, before
    being detected during a previous overhaul or any other previous maintenance program!

  3. Corrction.
    In a way, it was very “lucky”, that the “crack” on the SW 737-300 was three or
    more feet long and several inches wide, along the length of the fuselage and
    across several fuselage frames, allowing enough cabin air to escape in a very
    short time period, before causing much more damage!
    Had the crack gone across the fuselage, as it did on the Hawiian 737-200 in
    the 70s, this would either have been another “flying convertible” incident, or
    something far worse!

    However, there is NO excuse whatsoever, for a SECOND 737-300, or even a
    first with only 50,000 flight hours, to have experienced such an near fatal
    structural failure at SW, before being detected during a previous overhaul or
    any other previous maintenance program!

  4. Take a breath!

    Fatique cause seems to be chemical milling ( thinning ) in areas
    with no structure under the skin. i.e. enough material thickness
    to adequately hold rivets and reduced thickness in the areas
    between. The failure Works like a pull tab tin top.

    The material thickness step causes ( quite obviously ) excessive
    stress at/just after the step.
    IMHO an overly brilliant design feature to save on weight.

    The Aloha convertible in contrast had a cascading structure failure.

  5. WN’s aircraft have some of the highest number of cycles in the airline industry. Their 1995 B-737-300s were some of the last built of the Classic series, but they would still have somewhere north of 60,000 hours, and nearly (my guess) 55,000 cycles.

    But that shouldn’t make much of a difference to a well maintaned aircraft. This is yet another question about WN’s maintenance capability. This is the second incident of this type in two years. Also it wasn’t that many years ago WN was shelling out CFM-56 engines. IIRC, they lost about 4 or 5 engines in about 2 years.

    Perhaps WN needs more attention to corrosion control?

  6. IMHO – Low Cost = Low Maintenance.

    With some carriers you pay your money you take your chances.

    Just a question what is the average fleet life of Southwest, if this plane is 15 years old?

    • Low Mainttainance as cause would require the cracks to start at
      fastener holes or other places that can hold moisture and
      take corrosion damage. But not in homogenous and unbroken skin sections.

      My guess is that these failures are cycle based fatique initiated by
      distinct features of the production method.

      Chemical milling ( i.e. etching ) material removal is difficult
      to control and tends to go into grain interstices.
      This kind of milling produces a step change in material thickness.

      In my understanding all effects further fatique damage.

  7. from sw site re fleet life-age

    Fleet life SW from website

    The Company’s fleet has an average age of approximately 11.21 years.
    The average aircraft trip length is 648 miles with an average duration of one hour and 52 minutes.
    Southwest aircraft fly an average of 6 flights per day, or almost 10 hours and 51 minutes per day.
    Southwest was the launch customer for the Boeing 737-700 in 1997. Southwest was also a launch customer for the Boeing 737-500 and 737-300 series aircraft.
    Southwest recently completed updating its original color scheme of gold, red, and orange paint with the addition of Canyon Blue. Three Next-Generation Boeing 737 aircraft will continue flying with a commemorative livery of Desert Gold to honor the carrier’s original three cities-Dallas, Houston, and San Antonio.
    Performance- enhancing Blended Winglets have been added to our fleet of 737-700s, and all new 737-700 aircraft arrive from Boeing with Blended Winglets installed. Additionally, Southwest began installation of Blended Winglets on some of our 737-300 aircraft in early 2007; installation of Blended Winglets on these aircraft was completed as of the end of second quarter 2010.

  8. Pingback: Southwest 737 had fatigue cracks: ABC | AirInsight

  9. perhaps someone should explain to ” mr leeham : ;)) about skins ;-PP

    from the Kiro site

    A three-foot portion of the aircraft’s aft fuselage separated from the 737 in-flight. ..

    No it was not the fuselage that seperated – it was the SKIN on the aft fuselage section . .

    Methinks a copy editor at KIRO got confused . .

  10. from WSj

    NTSB Says Southwest Jet Had Pre-Existing Fatigue

    YUMA, Ariz.—Federal records show cracks were found and repaired a year ago in the frame of the Southwest Airlines Boeing 737-300 that made an emergency landing at an Arizona military base after a hole was torn from the passenger cabin.

    . . .

    An Associated Press review of Federal Aviation Administration records of maintenance problems for the 15-year-old plane showed that in March 2010 at least eight instances were found of cracking in the aircraft frame, which is part of the fuselage, and another half-dozen instances of cracked stringer clips, which help hold the plane’s skin on. The records showed that those problems were repaired.

  11. The emergency descent procedure includes these steps.

    CREW OXYGEN MASKS …………………………………….. ON

    PASSENGER OXYGEN …………………………………….. ON

    DESCENT …………….. ………………….H
    Without delay, close thrust levers, extend
    speedbrakes, and descend at VMO/MMO. Level off at
    lowest safe altitude or 10,000 feet, whichever is
    higher. If structural integrity is in doubt, limit airspeed
    and avoid high maneuvering loads.

  12. just found a second plane with similar cracks in same area. Would not have been caught on normal inspection- but maybe should have been caught on last heavy inspection.

    FWIW – a friend of mine since retired as a mechanic for a major airline mentioned years ago one of the ‘ positive’ ;-PP things about smoking on aircract. The negatives are well known, since the nicotine makes a mess in areas where there is condensation. However – nicotine stains made a fairly good tracking method for small cracks and leaks in the pressure hull around the passenger sections.

    If as described in the press ( big IF ) there were skin cracks along a lap joint, at the age of the plane, it is a good bet there will be some nicotine stains . . .

    • I am still looking for pics taken in sufficient detail from the _outside_ ?
      The inside pics tend to show the inner plastic stuffing and a bit of sky
      but no usefull detail.

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