Loose Bolt Might Have Caused Last Week's China Airlines Super Explosion

The Today Show reports that investigators think the China Airlines 737 that dramatically exploded on the runway last week may have been caused by a loose bolt. The bolt may have slipped from its washer on one of the slats used to slow the plane on landing, shot into the engine, puncturing the fuel tank and causing fuel to spray and ignite.

Airlines worldwide are urged to check the nut and bolt assemblies on 737 series 600 through 900. Stateside, these planes are flown by Continental, Southwest, Delta, American, and Alaska Airlines.

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  1. Buran says:

    A lot of crashes are caused by small things like this. Often, the root cause is a microscopic crack that is found using an electron microscope. (that is, a crack so small that optical microscopes can’t find it).

  2. boandmichele says:

    @Buran: i ask out of curiosity,

    what problems can arise from such a small crack? if anything gets through the crack it must be a small particle indeed. im interested to hear (and terrified) that such a small fissure can cause a whole plane to go down.

  3. Nemesis_Enforcer says:

    @Buran: Yep When I was in the Air Force I saw a million dollar engine on a F-16 eat a small piece of asphalt that had come loose and explode. It was kinda cool to see the flames shoot out the front and watch the pilot jump out like his pants were on fire. Luckily no one was hurt but Jet engines are very picky on what goes in.

  4. timmus says:

    On US Air, passengers will get 15 minutes of advance boarding time if they go out and do the inspections and sign the maintenance log in the cockpit. Flashlights and a flyer on what to look for will be provided at the gate, and flight attendants will provide a bar of Lava soap when the flashlights are returned.

  5. rbb says:

    Dang. I guess I better put that on my checklist when I go out shopping for used 737s this weekend…

  6. TechnoDestructo says:

    @boandmichele:

    The crack starts small. Then the crack gets bigger, and then it gets bigger faster and faster…over the course of several tiny fractions of a second, until the crack is big enough that passengers can fall through it.

  7. HeyThereKiller says:

    @boandmichele: Ever see a NASA shuttle try to reenter the atmosphere?

  8. boandmichele says:

    okay i was just thinking in terms of something leaking through the crack, not it expanding. i understand.

  9. @boandmichele:

    Aircraft are largely made of aluminum. Depending on where the crack is, and what the aluminum is holding together, the failure can be catastrophic.

    In the 80s, an Aloha Airlines 737 lost it’s roof on an inter-island flight when a fatigue crack (missed by poor inspections and caused by thousands of pressurization/depressurization cycles) peeled the roof off of the jet at altitude. Luckily, most people had their seat belts on, but the flight attendant went swimming and was never found.

    In 1979, a DC-10 crashed while leaving Chicago because the engine literally flew of of the wing, tore out hydraulic systems on that side of the jet, and caused an unrecoverable situation. To save time, American’s mechanics had developed a different method of removing engines from the plane for maintenance that caused a stress riser (precursor to a crack) in the strut that hold the engine onto the airplane. The riser developed into a crack, and the crack caused the engine mount to fail suddenly during takeoff.

    That said, Ben has a detail wrong here; the bolt in question was pushed through the wing tank by the retraction of the leading-edge slats, causing a leak; NG 737 engines, if they fail catastrophically (which almost never happens) have an extremely tiny likelyhood of causing a fire because of the kevlar containment collar around the engine’s rotating bits.

  10. NG 737 engines, if they fail catastrophically (which almost never happens) have an extremely tiny likelyhood of causing a fire because of the kevlar containment collar around the engine’s rotating bits.

    To clarify; the NG 737′s engines (CFM-56 family) are some of the most reliable in the air, but if one does fail, it’s extremely unlikely that it would be an “uncontained” failure, in which parts shoot out of the engine in all directions; more likely, the engine will simply be shut down, or the fire supression system will be activated by the pilot.

  11. bilge says:

    First uncommanded rudder deflections, now this shit?

  12. Buran says:

    @Nemesis_Enforcer: Depends on the engine and what goes in. Ever see those videos of frozen chickens (from a grocery store, I assume) going into 777 engines?

  13. Buran says:

    @HeyThereKiller: That was a different kind of crash and wasn’t caused by FOD damaging an engine but instead damaging a different vital structure.

  14. Buran says:

    @CaliforniaCajun: The AA crash was caused in part by the pilots actually reducing speed when the engine was lost. Had they not done this, the aircraft would likely have been recoverable. The immediate cause of the crash was a combination of the slats deploying (when the hydraulic lines were damaged) and the pilots slowing down below the stall speed of that wing.

    The left wing stalled, the right wing didn’t, the a/c rolled to the left, went inverted, and went into the ground.

  15. gibsonic says:

    they should have just let Ford make that plane. They use bigger better bolts you know.

    [www.youtube.com]

  16. ceejeemcbeegee is not here says:

    Guess this means people can’t complain when their flights are delayed. I’d rather be late than be on fire.

  17. boandmichele says:

    werd. thanks all. good interesting stuff.

  18. homerjay says:

    Bolt was probably made in China….

    /Sarcasm

  19. Dr. Eirik says:

    @Buran: A contributing factor in Chicago was that the loss of the engine had also caused loss of a number of the cockpit systems, including the stick shaker. The pilots likely didn’t realize that they were in a stall until it was too late. In a book I read about the crash some years ago, most pilots were able to land the plane in a simulator, but acknowledged that knowing the details of the crash gave them warning.

    But if you want to talk about small cracks taking down an aircraft, you don’t have to look any farther than the United DC-10 that crashed in Iowa some years ago. It was traced to a microscopic impurity in the original titanium that would later become the center of the fan disk. When it gave out, it wiped out the hydraulics.

  20. Wormfather says:

    @CaliforniaCajun: What a fine time for the FA to go for a dip. And we pay for service like this.

  21. Chairman-Meow says:


    What I’m still wondering is if or when the pilot (or co-pilot) pulled the fire handles for that engine when it went up. I’m sure the cockpit caution & warnings lights were all lit up like a Christmas tree and the klaxon were bleating like mad.

    For those who have never been around jet engines. When an engine fails, they tend to do so in a most spectacular fashion; especially if the failure occurs by either FOD (Foreign Engine Debris) or if the compressor turbine blades fail.

    I’ve seen engines tear themselves to pieces because of a loose bolt or a forgotten tool left in the intake. I’ve also seen the end-result of when an improperly attached engine sheared away from the engine mounts and attempt to fly on its own. I’ve also seen what happens when the primary compressor blade assembly comes apart, rips through the cowling, and shreds everything (and everyone) in its path.

    They are really nasty beasts when they misbehave.

  22. JayXJ says:

    @boandmichele:

    The Challenger explosion was caused by a hairline crack in a rubber O-ring…

  23. Ncisfan says:

    Makes sense

  24. gibsonic says:

    @JayP71:

    …as was my 2nd child.

  25. Starrionx says:

    @front_towards_enemy

    This wasn’t an engine fire. The engine ignited the fuel that had leaked from the tank. The problem was caused by the loose bolt getting caught by the slats retracting. Once the plane stopped moving, the fuel accumulated and then ignited. The pilots were supposedly unaware there was a problem.

  26. FLConsumer says:

    Airplane – (n) lots of parts flying in close formation.

  27. boandmichele says:

    @JayP71: well i knew that. very tragic. i grew up wanting to be an astronaut. but hairline and electron-microscope visible are different, no?

  28. JayXJ says:

    @gibsonic:

    Hahaha. Now let me wipe up this coffee…

  29. Buran says:

    @Dr. Eirik: The UA232 crash was an amazing feat of airmanship in the end, though, because the crew ALMOST saved the aircraft by using thrust vectoring. They only missed the runway at the very last moment. The mistake there was running all three hydraulic lines through the same spot where all three could get damaged at the same time.

    The AA DC-10 didn’t have a stick shaker on the First Officer’s stick (just on the captain’s), so the F/O didn’t realize the plane was stalling (which is another reason to say that throttling back the remaining engines was a bad idea; don’t know if you’re stalling, don’t touch anything!). Now, it’s impossible to order an aircraft that’s required to have shakers without one on the F/O stick due to that mistake. Douglas deciding to be cheap cost a lot of lives.

    I just wish aircraft makers would be more proactive about remedying design problems like that before people die, instead of our “wait til someone dies, then find the problem, have a nonbinding recommendation come out, then MAYBE have a binding one be released later, often after more people die”.

    The reason they don’t? They’re too cheap.

  30. Buran says:

    @JayP71: Eh. Sort of. The O-ring didn’t flex as it should have, due to the unusually cold temperatures at the pad that morning, and hot gases leaked past it. Not really a crack but definitely a cold-related problem.

    Fix: revise joint to add a third O-ring.

    There was a proposal to build a “monolithic” SRB that wouldn’t have had the dangerous joints that caused the explosion but it was rejected — twice — because the head of the Senate committee in charge of the selection process was from Utah and made sure that Thiokol got the contract.

    Cheapness and politics FTL.

  31. jeff303 says:

    Man, did anyone else read that as “loose belt”?

  32. Chairman-Meow says:

    @Buran:

    Actually, It was AA who ordered the planes without the stick shaker in the F/O position.

    Douglas offered the aircraft with both options. Boeing offed the same option in their aircraft as well. This was in the days before “open cockpit” where the pilot was IN CHARGE and the F/O was mostly along to watch.

    There is an excellent series of books by Job Mc Arthur called: AIR DISASTER (vols 1-4) That covers many of these accident. All of them are excellent reads. You can find tham at [www.amazon.com]

  33. OPNLguy says:

    >>>The Today Show reports that investigators think the China Airlines 737 that dramatically exploded on the runway last week may have been caused by a loose bolt. The bolt may have slipped from its washer on one of the slats used to slow the plane on landing, shot into the engine, puncturing the fuel tank and causing fuel to spray and ignite.

    This kind of media hyperbole is yet another example of how they “spice-up” a story for their own purposes.

    It *didn’t* happen on a runway-it happened as the aircraft stopped at its parking place.

    It *didn’t* explode, dramatically or otherwise. Yes, there was a small fire, and it ended up turning into a big fire. What looked like one or more “explosions” from the bottom of the aircraft were main landing gear tires losing their 200 psi pressure. That pressure release moved some flames around as well as upward, and while it looked like a “fireball” it really wasn’t one-the “explosion” from that supposed “fireball” didn’t result in a major breach of the wing tanks that would have rapidly spread the fire underneath the aircraft.

    The slipped bolt *didn’t* “shoot” or otherwise go into the running engine. First, the engines had already been shutdown, since the aircraft had arrived at its parking spot. Secondly, there have already been pictures released that were taken from *inside* the wing fuel tank that clearly show how and where the fuel tank was breached by the slat hardware when the slats were being retracted.

    For the last 40 years, *all* 737 models (not just this latest “Next Gen” version) have shared the same design of how the slats retract into the wing, and since no other aircraft have burned up like this China Airlines flights has, it strongly suggests that the 737 is a sound design. The accident aircraft recently had been through a major maintenance check where the slats had been removed, and conventional wisdom is leaning towards the theory that they were not properly reinstalled, i.e. it’s a *human* problem, and *not* an aircraft problem.

    But hey, the folks at the Today show are all professional accident investigators, and we call take what they say as 100% Gospel. (Not!)