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777 fan-blade / cowling failure over Denver

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  • #76
    Originally posted by Gabriel
    I don't thing that ejected back would have this much energy. Probably broke the shaft.
    Actually, looking at the cutaway, two of the LPT rotors are aft of the shaft rear bearing. But that entire section must have blown up! And that's a BIG hunk of metal!

    https://i.pinimg.com/originals/a7/35...fcf6737ba1.jpg

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    • #77
      I have a question for the panel. There is a big story in the Wall Street Journal about this topic. They repeatedly say that the cowling came off because it was damaged by forward flying fan blade debris. I had thought that the cowling failed from the intense vibration so well described by Capt. Benham, and seen in the videos. What about this?

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      • #78
        Originally posted by lapzdplt View Post
        I have a question for the panel. There is a big story in the Wall Street Journal about this topic. They repeatedly say that the cowling came off because it was damaged by forward flying fan blade debris. I had thought that the cowling failed from the intense vibration so well described by Capt. Benham, and seen in the videos. What about this?
        The "sliced by forward-flying blade" hypothesis is plausible. Check the previous coverage in the Blancolirio channel on this subject.

        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
        --- Defend what you say with arguments, not by imposing your credentials ---

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        • #79
          Thanks. I'm a fan of Blancolirio and he lives about 40 miles from me. I watched three of his videos: https://www.youtube.com/watch?v=HDxcBWZUCTI on SWA1380, https://www.youtube.com/watch?v=5hyP07BJAic&t=361s on UAL1175, and https://www.youtube.com/watch?v=EwNCCrjMmeg&t=317s on UAL328. The opening of the one on 1175 is pretty impressive, with the test engine failing spectacularily and stuff coming forward. It looks like the inlet of the 328 engine is aluminum, since it came to rest on the ground in one piece with just the blade slice through it. I wonder what boeing will do with their cowlings, since it seems they can't take either the concussive forces transmitted through the containment structure, or the aerodynamic forces generated without an inlet. Is it time to go back to a more malleable product e.g. aluminum? Seems like something should change as it may not be possible to totally prevent fan blade failures. Has Airbus just been lucky?

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          • #80
            The NTSB made an thorough investigation of that in the UAL 1175 incident, detailing the differences between the test conditions and te actual conditions including differences in the inlet and cowling.

            https://data.ntsb.gov/carol-repgen/a...port/96738/pdf
            I think there is a docket also available with more detailed documents and information prepared by the individual investigation groups (the source used to prepare the final report)

            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
            --- Defend what you say with arguments, not by imposing your credentials ---

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            • #81
              Originally posted by lapzdplt View Post
              Has Airbus just been lucky?
              Air France flt 66, an A380, experienced a similar loss of the fan inlet and forward cowling structures. In this case, the entire fan hub failed. It might have fared better in a single blade off event.

              https://www.bea.aero/uploads/tx_elyd...17-0568.en.pdf

              Loss of cowling doors is more common, usually due to improper latching.

              https://news.aviation-safety.net/2018/12/01/timeline-of-occurrences-and-regulatory-actions-on-airbus-a320-family-engine-fan-cowl-door-loss-incidents/

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              • #82
                Originally posted by Gabriel View Post
                The NTSB made an thorough investigation of that in the UAL 1175 incident, detailing the differences between the test conditions and te actual conditions including differences in the inlet and cowling.

                https://data.ntsb.gov/carol-repgen/a...port/96738/pdf
                I think there is a docket also available with more detailed documents and information prepared by the individual investigation groups (the source used to prepare the final report)
                To quote: "The aluminum structure has the ability to yield and absorb the same amount of energy and redistribute the FBO loads between the fan case and the inlet without

                Page 10 of 12 DCA18IA092

                causing failure to the inlet and the fan case to inlet attachment.

                So why doesn't the report suggest using Aluminum rather than carbon fiber for these areas?

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                • #83
                  Originally posted by lapzdplt View Post

                  To quote: "The aluminum structure has the ability to yield and absorb the same amount of energy and redistribute the FBO loads between the fan case and the inlet without causing failure to the inlet and the fan case to inlet attachment."

                  So why doesn't the report suggest using Aluminum rather than carbon fiber for these areas?
                  Well, the report doesn't make any suggestion or recommendation whatsoever, even regarding the fan blade failure or it faulty inspection.

                  In addition, I don't think that would be a good recommendation, mandating specific materials, techniques, etc would hinder innovation. The recommendation should be to enact design, testing and certification standards that take into account these failure modes. For example, that a production-compliant engine must be tested (for the fan fracture test) with a production-compliant inlet and a production-complied, and making a requirement that the inlet and cowling shall not separate from the engine during such an event.

                  The little problem with that is that engines and planes are certified separately (since the same engine can eventually be used in different planes and the same plane can be offered with different engine options). So P&W is the owner of the engine's certificate and Boeing is the owner of the 777 certificate, and guess what, the cowling is part of the plane, not part of the engine, si it falls under Boeing's certificate. So including the Boeing's cowling in the P&W testing is complicated, and also not clear who would bear the responsibility if the test filas and the cowling separates. Not to mention that an engine may be used in many different plane designs and it is not feasible or rational to repeat the fan blade fracture test with the same engine type but with all the different cowling designs, or redo the test if a plane manufacturer selects that engine for a new airplane type years after the engine certification. Yet, regarding these complexities, something along these lines should be done. If not, it will be done when a cowling separation kills people.

                  --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                  --- Defend what you say with arguments, not by imposing your credentials ---

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                  • #84
                    Originally posted by Gabriel View Post

                    Well, the report doesn't make any suggestion or recommendation whatsoever, even regarding the fan blade failure or it faulty inspection.

                    In addition, I don't think that would be a good recommendation, mandating specific materials, techniques, etc would hinder innovation. The recommendation should be to enact design, testing and certification standards that take into account these failure modes. For example, that a production-compliant engine must be tested (for the fan fracture test) with a production-compliant inlet and a production-complied, and making a requirement that the inlet and cowling shall not separate from the engine during such an event.

                    The little problem with that is that engines and planes are certified separately (since the same engine can eventually be used in different planes and the same plane can be offered with different engine options). So P&W is the owner of the engine's certificate and Boeing is the owner of the 777 certificate, and guess what, the cowling is part of the plane, not part of the engine, si it falls under Boeing's certificate. So including the Boeing's cowling in the P&W testing is complicated, and also not clear who would bear the responsibility if the test filas and the cowling separates. Not to mention that an engine may be used in many different plane designs and it is not feasible or rational to repeat the fan blade fracture test with the same engine type but with all the different cowling designs, or redo the test if a plane manufacturer selects that engine for a new airplane type years after the engine certification. Yet, regarding these complexities, something along these lines should be done. If not, it will be done when a cowling separation kills people.
                    It should be the responsibility of the airframer to ensure that their fan-inlet and bulkhead structures can withstand an FBO event on the design-specified engine. It should be the responsibility of the engine manufacturer to ensure that their design and inspection process prevents FBO events to the greatest practical standard (which P&W failed to do with the PW4000), but, once a blade leaves the hub, we can't consider them responsibile for how the surrounding structures perform. If we did, the engine manufacturers would simply specify more robust materials that add weight and leave the consequent problems that creates to the airframer.

                    Ideally, it's a coordinated design and certification effort. The PW4000-112 was designed specifically for the B777 so there is no reason why it could not have been tested with the actual B777 fan inlet and bulkhead design. I really think this was just a lack of vision.

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                    • #85
                      Originally posted by Gabriel View Post

                      Well, the report doesn't make any suggestion or recommendation whatsoever, even regarding the fan blade failure or it faulty inspection.

                      In addition, I don't think that would be a good recommendation, mandating specific materials, techniques, etc would hinder innovation. The recommendation should be to enact design, testing and certification standards that take into account these failure modes. For example, that a production-compliant engine must be tested (for the fan fracture test) with a production-compliant inlet and a production-complied, and making a requirement that the inlet and cowling shall not separate from the engine during such an event.

                      The little problem with that is that engines and planes are certified separately (since the same engine can eventually be used in different planes and the same plane can be offered with different engine options). So P&W is the owner of the engine's certificate and Boeing is the owner of the 777 certificate, and guess what, the cowling is part of the plane, not part of the engine, si it falls under Boeing's certificate. So including the Boeing's cowling in the P&W testing is complicated, and also not clear who would bear the responsibility if the test filas and the cowling separates. Not to mention that an engine may be used in many different plane designs and it is not feasible or rational to repeat the fan blade fracture test with the same engine type but with all the different cowling designs, or redo the test if a plane manufacturer selects that engine for a new airplane type years after the engine certification. Yet, regarding these complexities, something along these lines should be done. If not, it will be done when a cowling separation kills people.
                      I understand and agree. A cowling separation has already killed someone-the pax on SWA 1380. Different engine, but similarities. That wing root on UAL 328 got torn up pretty good, too.

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                      • #86
                        Originally posted by lapzdplt View Post

                        I understand and agree. A cowling separation has already killed someone-the pax on SWA 1380. Different engine, but similarities. That wing root on UAL 328 got torn up pretty good, too.
                        Yes, and it had been an almost identical incident with another Southwest flight shortly before that one, except that one didn't end up with windows shattered and people dead.

                        In the investigation report of SWA 1380, the NTSB recommend...

                        Expand the Title 14 Code of Federal Regulations Part 25 and 33 certification requirements to mandate that airplane and engine manufacturers work collaboratively to (1) analyze all critical fan blade impact locations for all engine operating conditions, the resulting fan blade fragmentation, and the effects of the fan-blade-out-generated loads on the nacelle structure and (2) develop a method to ensure that the analysis findings are fully accounted for in the design of the nacelle structure and its components. (A-19-20)
                        I don't know what action, if any, the FAA took in that regard. (Note: part 25 is design requirements for transport category airplanes, and part 33 is for aircraft engines.

                        Investigation report:
                        https://www.ntsb.gov/investigations/...ts/AAR1903.pdf

                        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                        --- Defend what you say with arguments, not by imposing your credentials ---

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