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  • Turbojet engine failure prevention

    Turbojet Engine Failure Prevention

    THREE Boeing airliners recently suffered in-flight uncontained engine failures in as many days, the last weekend of February 2021. A United Boeing 777 out of Denver AND a Delta Boeing 757 out of Atlanta AND a Longtail Boeing 747 out of Holland. Engine parts were scattered across the countryside, damaging homes and vehicles, luckily only injuring a few people. All aircraft suffered minor damage, but if any had a fuel tank ripped open, they would have most likely caught fire and crashed, killing all on board; as has happened to many other aircraft.

    This has prompted me to explain why I tried, years ago, to develop an in-flight turbojet engine failure warning system and how it was canceled. I only wish I had tried harder.

    Hundreds have been damaged or destroyed and thousands of lives lost in the past to uncontained engine failures; which might have been saved. It is only a matter of time before another uncontained engine failure throws blades or buckets into cabins, fatally wounding passengers, or rips apart fuel tanks or controls, crashing the aircraft.

    The first passenger jetliner, DH-106 Comet, had engines inside wings for aerodynamic efficiency, but also wrapped in armor to contain engine failures. Later passenger jets had their engines mounted outside on “fuse-able bolts”, so a failing engine could be ejected before it caused more damage. However, Concord had engines in its wings.

    Crack detection inspections of compressor blades every 3,000 hours has apparently not reduced the failure rate, which may progress from a crack to stress rupture in a few hundred hours or less. Fortunately, cracked blades don't rupture immediately, as some have maintained, which would also make even 1,000 hour inspections worthless.

    Foreign Object Damage or Hydrogen Embrittlement Cracks?

    In 1958, USAF/OCAMA initiated a study of Foreign Object Damage (FOD) limits on compressor blades as related to engine failures, since engine failures were becoming relatively frequent and the manufacture's FOD limits were suspect. I and others were tasked by the USAF to determine the limits of FOD to be allowed during overhaul.

    However, I concluded the cause of most failures was Hydrogen Embrittlement cracking on the convex mid span surface; where engineers allowed the greatest FOD damage. Failures also seemed to be associated with vibration during compressor stall. Here the flexing of blades could result in a migration of hydrogen atoms into grain boundaries, forming hydrogen molecules. In time, enough of these molecules might collect and split crystal grain boundaries, leading to cracking and eventual stress rupture.

    In 1959, I wrote an investigation summary and suggested the use of a device to detect impending failures; sending it to USAF/WPADC. I insisted it might be better to develop an in-flight detection device to warn of any decreasing clearance in the gap between the inside of an engine's housing and a blade's tip; the first sign of impending failure. I also insisted that vacuuming runways to eliminate the ingestion of foreign materials and then blaming FOD after engine failures might not be realistic or cost effective.

    There was no reply from USAF/WPADC, but the manager of GE engine development wrote to my boss, possibly complaining about my efforts and noted, “We have NOT conducted any vibratory stress studies on the subject blades”, citing the lack of slip rings. However, I found slip rings were available from a supplier in Chicago which could transmit strain gauge readings on blades in an operating engine to recorders.

    We determined the maximum stress was in an area of the blades where GE engineers allowed the maximum amount of FOD to be approved during engine overhaul and the lowest stress was on leading edges, where GE restricted the least amount of FOD.

    1960, my work was recognized in a USAF/OCAMA report on FOD limits, but no mention was made of any suggestion or need to detect impending engine failures. So I resigned my position to develop my own version. This involved running an import car repair garage along with spending long hours designing test equipment and trying to obtain information, used blades and an operational engine to run with cracked blades.

    Fortunately, a scrap metals dealer allowed me to sort thru his piles of rejected blades; from USAF/OCAMA. I found many cracked, using dye penetrate, with evidence of repeated service periods. These appeared as “tree rings” when broken apart. Clearly, there was no danger of sudden failure when the crack started and blade separated.

    Oden Research Corp

    1963, I formed a stock company to develop my earlier USAF/OCAMA suggestion, which was progressing nicely. I then submitted an application for a federal grant to pay for a destructive test using an operating engine. I hoped to develop my system as a means of preventing in-flight contained or uncontained engine failures, even bearing failures.

    June 20, 1965, Pan Am Flight 843, 707-321B, on take-off from San Francisco, the #4 engine or right outboard had an uncontained failure. The engine tore loose, went right and ripped off 25 feet of the right wing. (The pilot was still able to land safely!)

    This event convinced Larry Booda, Aviation Week Editor, to arrange my appearance before the Senate Subcommittee on Aviation Safety; regarding my failure warning system. There a civilian engineer testified my device might work in theory, but was not useful because blade failure happens too quickly to be detected. (Yet cracked blades with evidence of repeated service periods or safe flight hours were often found during engine overhaul at USFA/OCAMA; later found by me in a metal dealer's salvage yard.)

    A military engineer testified that USAF policy was “Fly to Fail” and depend on ejection seats to save the crew or for the engines to ejected "safely" on multi-engine aircraft. He claimed the addition of more gauges or warning lights would be “Distracting”.

    After the hearing was over, a young man came to me and said, "We are already using a version of your device in our test cells to prevent damage from uncontained failures during development testing.” (There is a record of several test cells, within armored buildings, being destroyed by uncontained engine failures.)

    I asked, and still ask, “Why not use your blade tip gap clearance detection in-flight?” He walked away without any reply. Later, the committee rejected my application.

    On my return home, the scrap metals dealer, from whom I obtained cracked blades rejected by USAF/OCAMA and who promised me a free operational engine for testing my blade tip gap clearance detection device, asked to meet me at the local airport. Then he asked to walk out to my airplane where we might not be overheard. Then he said, “You really pissed off someone important. I can't allow you to come around again.” That ended my efforts to develop an impending engine failure warning system.

    I eventually became a new car dealer and local Civil Air Patrol Squadron Commander; with 26 years of service. I also have an active interest in the commercial uses of Hydrogen and my company has been drilling for same as a fossil fuel alternative.

    ROTOR BLADE MONITORTM Turbojet Engine Failure Warning System

    One model with two modes were considered. One mode for use in maintenance intervals. The other mode as an in-flight warning of blade tip gap reduction or blade elongation, which has an unknown time period before stress rupture and engine failure.

    However, blades and buckets apparently do not fail immediately when cracks and elongation becomes evident, whether said to have been caused by FOD or Hydrogen Embrittlement. 3,000 hour inspections appear routine, with 1,000 hour inspections being considered.

    Maintenance Mode consisted of a dual electrode spark plug fitted to engine inspection ports that allow the inspections of individual rows of compressor blades or turbine buckets.

    A central electrode, projecting “X” inches inside the engine housing, is centered inside a circular electrode, mounted flush with the engine housing. An electronic spark is passed between the electrodes, with a gap of “X” inches, while blades or buckets have a tip gap clearance inside the engine of “3X” inches.

    When the blades/buckets start cracking, centrifugal force moves the tips outward. It is worth noting that blades/buckets function as in-line springs, with their crystals able to flex ever so slightly. How much they extend at 80% of max RPM is the basis of my warning system. Of course this “3X” blade tip gap inside the engine dimension varies with different engines.

    The frequency of the spark could be varied to correspond to near engine RPM, allowing each blade or bucket tip gap to be examined for its extension in apparent slow motion.

    When a cracking blade/bucket extends more than “X” distance, it will be closer to the central electrode than the “X” distance to the circular electrode. The spark will then travel to the tip of the elongated blade/bucket, not to the second electrode. The absence of spark to the second electrode would be noted. With the addition of a timing feature, any elongated blade/bucket could be located exactly where it may be found on the hub.

    I had envisioned an aircraft taxiing to a maintenance hanger, an analysis consul plugged into a fitting on the engine and all blades and buckets, even bearings, checked for elongation or wear in a relatively short period of time. Then, if a blade or bucket or bearing was found to be elongated or worn, the engine could be promptly exchanged and sent to overhaul, and the aircraft returned to service; a more cost effective system than before.

    In-Flight Mode consists of the same dual electrode spark plug with the main electrode still projecting into the engine housing “X” distance; now acting as a rub point. When a blade or bucket tip in any row of any engine extends more than ”2X” distance, it will touch the rub point. This grounds a circuit, sending an individual engine's signal to a warning light in the cockpit. The pilot then takes action as is useful. Only one light needed per engine.

    Hundreds of cracked and elongated blades that have rubbed the inside of their engine housings have been found during overhaul, indicating hours of operation after elongation. So the pilot might take note of an engine with a blade or bucket elongating, reduce power on the identified engine, try to avoid compressor stall, and make a safe landing.

    The in-flight warning system was in my suggestion to USAF/WPADC in 1959. Whereas the Maintenance Mode Model was what I was trying to develop before I testified in the Senate aviation safety committee hearing. Then I was effectively prevented from doing more. My hope is that someone might be able to convince an engine manufacturer to install what I was told was a similar warning system into engines used in-flight and save lives.

  • #2
    Sorry. I could not read past the 1st paragraph.

    Originally posted by co80610 View Post
    ]THREE Boeing airliners recently suffered in-flight uncontained engine failures in as many days, the last weekend of February 2021. A United Boeing 777 out of Denver AND a Delta Boeing 757 out of Atlanta AND a Longtail Boeing 747 out of Holland. Engine parts were scattered across the countryside, damaging homes and vehicles, luckily only injuring a few people. All aircraft suffered minor damage, but if any had a fuel tank ripped open, they would have most likely caught fire and crashed, killing all on board; as has happened to many other aircraft.
    United 777 out of Denver definitively was not an uncontained engine failure (confirmed by the NTSB), Longtail 747 as far as I know was not an uncontained engine failure either, Delta 757 I don't even know of what incident you are talking about (if it is DL2123, I have seen nothing that indicates that parts departed the engine, let alone that it was an uncontained engine failure). And can you pelase list some of the "to many other" where, as the result of an engine failure, "had a fuel tank ripped open, caught fire and crashed, killing all on board"?

    Start providing evidence to sustain your ridiculous claims or, I'd suggest, shut the f**k up.

    --- 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 ---

    Comment


    • #3
      Originally posted by Gabriel View Post

      Start providing evidence to sustain your ridiculous claims or, I'd suggest, shut the f**k up.
      Shit stirring little asswipe isn’t he ! Why does he mention Concorde in his diatribe. That crashed as a result of FOD picked up on the runway penetrating the fuel tank. There was no engine failure.

      If it 'ain't broken........ Don't try to mend it !

      Comment


      • #4
        Originally posted by brianw999 View Post

        Shit stirring little asswipe isn’t he ! Why does he mention Concorde in his diatribe. That crashed as a result of FOD picked up on the runway penetrating the fuel tank. There was no engine failure.
        I wouldn't know. I could not make it past the 1st paragraph.

        --- 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 ---

        Comment


        • #5
          Originally posted by co80610 View Post
          The in-flight warning system was in my suggestion to USAF/WPADC in 1959. Whereas the Maintenance Mode Model was what I was trying to develop before I testified in the Senate aviation safety committee hearing. Then I was effectively prevented from doing more. My hope is that someone might be able to convince an engine manufacturer to install what I was told was a similar warning system into engines used in-flight and save lives.
          It's a noble idea, but is it practical? You pointed out that the Comet had engines encased in armour. Obviously, this wasn't practical. The armour needed to contain a rotor disk fragment on a PW4000 would be entirely impractical. In your proposal, have you considered the potential causes for spurious warnings and the potential rate of spurious warnings? Have you considered what the procedure would be for such a warning? Diversions are very costly and disruptive. Continuing to destination with such a warning could present liability issues if an engine failure followed. Futhermore, I'm confused about why an in-flight warning would be needed at all if the maintenance warning is functional. You, yourself, stated that these cracks do not occur spontaneously, so a daily or weekly check should suffice, no?

          Also, this is 1960's tech using mechanical measurements. Can't a better system now be developed using laser measurements or other sensor technologies?

          The investigation of the FBO event experienced by United 1175 revealed a deplorable situation at Pratt & Whitney in which the affected blade had not been properly inspected, specifically, that the metal fatigue WAS detected but the inspector was not properly instructed on how to interpret the results of the new technology scans. Therefore, with properly trained inspectors, these fatigue issues would have been detected and the in-flight FBO events experienced on the PW4000-112's would have never occurred. That is how you prevent such occurrences.

          Moreover, many catastrophic engine failures occur for reasons unrelated to fan blade separation. Rotor disks fail. Oil pipes fracture. Etc.

          The problem to solve, it seems to me, involves more reliable (and competent) ground inspections. That means better oversight. Once the airplane leaves the ground with a flawed engine, something has already catastrophically failed: aviation safety itself.

          Comment


          • #6
            From Evan: Moreover, many catastrophic engine failures occur for reasons unrelated to fan blade separation. Rotor disks fail. Oil pipes fracture. Etc.

            The problem to solve, it seems to me, involves more reliable (and competent) ground inspections. That means better oversight. Once the airplane leaves the ground with a flawed engine, something has already catastrophically failed: aviation safety itself.


            EVAN: Sincerely appreciate your intelligent analysis and suggestions. I did consider the possibility of false warnings. The rotor components develop considerable centrifugal force and do not want to change direction when the aircraft does the same. As a result in fighter aircraft the blade tips apparently rub the engine housing at the top and bottom, but not the sides. The B-47, my project issue, had no such problem, so I didn't anticipate a jet liner to have one either. However, one solution might be to place the sensing devices in the sides of engine housings and have a reset button in the cockpit.

            I agree that better trained inspectors are needd in regard to fan blaces and discs, however, inspection now apparently only involves the fan bades and rotor discs. No inspections of interior compressor blades and turbine buckets seem to be done until 3,000 hours or perhaps now at 1,000 hours. Inspections of interior rotor discs, compressor and turbine, don't seem to be done ar all, but some have failed in rare instances with disasterous results.

            I agree my device is 1960s tech, but a blade or bucket tip rub point is about as current and physical as I can imagine. Signals could be sent by radio and laser measuring might be possible. However, I have been prevented from doing more by parties unknown since 1965. I can only complain that if such a warning system exists, as I was told, why is it not installed in aircraft to prevent some failures. Just the avoidance of law suites by 'terrified' passengers when an engine fails might save the airlines money.

            Comment


            • #7
              Gabriel: United 777 out of Denver definitively was not an uncontained engine failure (confirmed by the NTSB), Longtail 747 as far as I know was not an uncontained engine failure either, Delta 757 I don't even know of what incident you are talking about (if it is DL2123, I have seen nothing that indicates that parts departed the engine, let alone that it was an uncontained engine failure). And can you pelase list some of the "to many other" where, as the result of an engine failure, "had a fuel tank ripped open, caught fire and crashed, killing all on board"?

              Start providing evidence to sustain your ridiculous claims or, I'd suggest, shut the f**k up.



              Apparently you don't read much. I also have little respect for you or the NTSB, if what you write is true.

              United Airlines Flight 328, bound for Honolulu, reported right engine failure shortly after leaving Denver International Airport at 12:49 p.m. The engine also caught fire and began to disintegrate as terrified passengers recorded the failing engine burning in flight. On landing a large hole was found punctured into the fuselage.

              On the ground, one home had a three foot hole punched in its roof by debris that were reported to have narrowly missed an occupant. In addition a pickup was totaled by an inlet ring crashing on to it. Other parts rained down on yards, with people out of doors on a sunny day.

              Also, the engine of Longtail Aviation Flight 5504, a Boeing 747 freighter flying from the Netherlands to New York City, exploded shortly after takeoff, causing engine parts to shower the Dutch town of Meerssen. Two people were injured by the falling debris, and the aircraft, operated by the Bermuda-headquartered charter company Longtail Aviation, landed safely in Belgium.

              Looks like the Delta 757 engine failure was contained, my bad, just terrified passengers.



              Comment


              • #8
                From Brian999: Shit stirring little asswipe isn’t he ! Why does he mention Concorde in his diatribe. That crashed as a result of FOD picked up on the runway penetrating the fuel tank. There was no engine failure.

                Brian999: I was discussing engine placement and included the Concorde design, to keep some fault finding nitwit like you from pointing out my error for not including it as a non-outside the wing design.

                I resent your disgusting insult as well. I spent five years of my life trying to design a device to save lives, then 26 years doing the same with the CAP aka Come And Pay. The Air Force only pays for fuel on official search missions,, some of which involve arriving at 4 AM for briefing, then flying a hundred miles to search a specific sector. for a downed aviator or lost hiker or the like. We are the first, responders in many cases. Also when heart problems limited flying, I served as an Aviation Exploring Post Advisor and was later appointed as a Commissioner. You??

                Comment


                • #9
                  Oh boy, this is going to take at least 4 containers of popcorn. Going to sit back, relax and wait for the show to start!

                  Comment


                  • #10
                    Originally posted by co80610 View Post
                    I agree that better trained inspectors are needd in regard to fan blaces and discs, however, inspection now apparently only involves the fan bades and rotor discs. No inspections of interior compressor blades and turbine buckets seem to be done until 3,000 hours or perhaps now at 1,000 hours. Inspections of interior rotor discs, compressor and turbine, don't seem to be done ar all, but some have failed in rare instances with disasterous results.
                    You're not really addressing my point however. Why do we need an in-flight fan blade failure warning system when competent engine inspections will reveal these impending failures on the ground? Again, the problem is that flawed engines are not being detected on the ground. They don't just suddenly develop metal fatigue during flight. The solution seems to be **competent** inspections at predictable service life intervals where the blades are removed and scanned for cracks and metallurgy issues. The problem seems to be that these inspections, which did reveal impending failures, were ****incompetent**** and therefore the blades were placed back in service. When you developed your ideas, hollow core fan blades had yet to be introduced, and now composite blades are becoming feasable. Any flaws need to be detected on the ground during scheduled maintenance, that is the only sensible defense against catastrophic engine failure.

                    Comment


                    • #11
                      Originally posted by co80610 View Post
                      Gabriel: United 777 out of Denver definitively was not an uncontained engine failure (confirmed by the NTSB), Longtail 747 as far as I know was not an uncontained engine failure either, Delta 757 I don't even know of what incident you are talking about (if it is DL2123, I have seen nothing that indicates that parts departed the engine, let alone that it was an uncontained engine failure). And can you pelase list some of the "to many other" where, as the result of an engine failure, "had a fuel tank ripped open, caught fire and crashed, killing all on board"?

                      Start providing evidence to sustain your ridiculous claims or, I'd suggest, shut the f**k up.



                      Apparently you don't read much. I also have little respect for you or the NTSB, if what you write is true.

                      United Airlines Flight 328, bound for Honolulu, reported right engine failure shortly after leaving Denver International Airport at 12:49 p.m. The engine also caught fire and began to disintegrate as terrified passengers recorded the failing engine burning in flight. On landing a large hole was found punctured into the fuselage.

                      On the ground, one home had a three foot hole punched in its roof by debris that were reported to have narrowly missed an occupant. In addition a pickup was totaled by an inlet ring crashing on to it. Other parts rained down on yards, with people out of doors on a sunny day.

                      Also, the engine of Longtail Aviation Flight 5504, a Boeing 747 freighter flying from the Netherlands to New York City, exploded shortly after takeoff, causing engine parts to shower the Dutch town of Meerssen. Two people were injured by the falling debris, and the aircraft, operated by the Bermuda-headquartered charter company Longtail Aviation, landed safely in Belgium.

                      Looks like the Delta 757 engine failure was contained, my bad, just terrified passengers.


                      You are mostly correct in the description of the events, but still these were NOT uncontained engine failures.

                      Longtail:
                      When a turbine blade breaks it will go somewhere. If it goes out of the engine through the tailpipe, it is not an uncontained engine failure.

                      Delta:
                      When a fan blade breaks, it has to go somewhere. The fan blade is making a huge force forward (the fan blades are providing most of the engine thrust), so the fan bale will tend to fly forward. A blade leaving the engine through the front, is not an uncontained engine failure.
                      A blade fling out of the front of the engine may slice through the intake lip. That's not an uncontained engine failure.
                      A severed intake lip may lose structural integrity and fall out of the engine. That's not an uncontained engine failure.
                      With the lip gone, additional part of the engine fairing / cowling may fly off due to aerodynamic forces. That is not an uncontained engine failure.
                      The engine of United 380 caught fire, or rather some of its external accessories caught fire, oil-fed fire. There was no fuel fire and no any fire inside of the engine casing. There was no engine explosion or disintegration. Actually, other than the fan section, the engine itself (inside of the casing and front to back) seems to be pretty much intact and I've heard that it would be repaired and that it would be a very expensive repair but still much cheaper than trashing the engine and selling the parts for spares.
                      There was no hole in the fuselage. There was damage to the wing-to-body fairing, which is a lightweight streamlining composite part with no structural function. The pressurized hull was not pierced. The damage to the fairing is consistent with blunt force, not high-energy debris. Most likely it was pieces of the cowling that separated from the engine. Had this same part hit the actual fuselage in the same way, you most likely would have no hole. That said, it is a very dangerous condition. There was a Southwest flight where a similar situation (a piece of cowling flying out of the engine) hit the fuselage near a window and, while the piece did not penetrate the fuselage, the window was broken and a person that was seating with the seatbelt had her torso pulled out of the plane and she died as consequence of blunt trauma to her head when he hit the fuselage with it.

                      An uncontained engine failure is, by definition, high-energy fragmentes / shrapnel piercing through the casing of the engine. As far as I now, there is no evidence of such an occurrence in any of the incidents you mentioned.

                      There are good and very impressive nice examples of uncontained engine failures. Here you have a few:
                      https://en.wikipedia.org/wiki/United...nes_Flight_232
                      http://avherald.com/h?article=43309c6d/0032&opt=235
                      http://avherald.com/h?article=49ffa115/0003&opt=235
                      But not the ones you mentioned.

                      I am not negating the risks and dangers of pieces of the engine falling out, but that is not uncontained engine failure which is much more critical.

                      And I am still waiting your list of some of the "to many other" where, as the result of an engine failure, "had a fuel tank ripped open, caught fire and crashed, killing all on board" that you mentioned.

                      --- 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 ---

                      Comment


                      • #12
                        Originally posted by Gabriel View Post
                        An uncontained engine failure is, by definition, high-energy fragmentes / shrapnel piercing through the casing of the engine.
                        I'm not sure about that. The FAA seems to consider fan-blade forward arc non-containment as uncontained engine failure. The issue involves any event where an engine part might cause collateral damage to the aircraft.

                        Originally posted by FAA AIA Project Report on High Bypass Ratio Turbine Engine Uncontained Rotor Events

                        Blade uncontainment

                        The rate of forward arc fan blade fragment non-containment has been reduced by several orders of magnitude since the first high bypass turbofans entered service. Recent designs of engines such as wide-chord fan blade designs have lower rates than the earlier generations of high bypass turbofans. The airplane level consequences of fan blade fragment forward arc non-containment are usually limited to a small number of superficial nicks, dents and holes in aerodynamic surfaces. A few events have resulted in one or two small holes in the pressure skin (of the order of two inches across). There has been one level 3 event due to forward-arc uncontainment; this involved damage to a hydraulic system in an adjacent engine strut/pylon. Design improvements have reduced the rate of casing uncontainment by blades by a factor of 50 since the first high bypass fans entered service. The airplane level consequences of casing uncontainment by blades vary according to the specific failure mode involved. Most events result in a small number of superficial nicks, dents and holes in aerodynamic surfaces. The release of multiple whole fan blades, or LPT vane/ nozzle spinning has resulted in more extensive damage.

                        Comment


                        • #13
                          Originally posted by BoeingBobby View Post
                          Oh boy, this is going to take at least 4 containers of popcorn. Going to sit back, relax and wait for the show to start!
                          Can we fire some Boeing executives, and fault some pilots?
                          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                          Comment


                          • #14
                            Originally posted by 3WE View Post

                            Can we fire some Boeing executives, and fault some pilots?
                            Now THAT'S FUNNY!

                            Comment


                            • #15
                              But I also noticed that some"posts" have been deleted recently!

                              Comment

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