Alternator drive coupling out of tolerance

Discussion in 'Aviation Mishaps' started by Rushie, Dec 4, 2019 at 4:02 PM.

  1. Rushie

    Rushie Pattern Altitude

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    I am so demented I can’t remember anything. I cannot find the thread where a small plane (can’t remember what kind other than single engine) crashed somewhere in the northeast (can’t remember what city) killing the pilot whose middle name was Richard (can’t remember his first or last name) his wife Betty and their daughter whose name I cannot remember, and the cause was determined to be something on the alternator was slightly out of tolerance leading it to shake itself apart and cause engine failure and severe vibration. I listened to the live ATC where they vectored him toward an airport, he said he wasn’t going to make it and they told him there was a highway to his right, but he was in IMC I think and couldn’t see it. They crash at the back of a house and it burns down but the family whose last name is Rice all escape, including a bunch of cats and dogs.

    It’s driving me nuts I can’t find that thread. Was it even this forum?
     
  2. GeorgeC

    GeorgeC En-Route PoA Supporter

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  3. Clip4

    Clip4 Final Approach

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    There was nothing on the alternator out of tolerance. What was out of tolerance was internal in the engine.
     
  4. Rushie

    Rushie Pattern Altitude

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  5. Doc Holliday

    Doc Holliday Line Up and Wait

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    The coupling is a part of the alternator assembly.

    From the report:

    An examination of the engine revealed that the alternator drive coupling had failed, which resulted in damage to other internal engine components and ultimately resulted in a catastrophic engine failure due to a lack of oil lubrication. The investigation identified two possible conditions that could result in the coupling failure; but was unable to determine which was more likely. First, it is possible for components of the coupling to progressively move out of tolerance due to repeated "slip testing," which is a procedure the engine manufacturer prescribed to be performed anytime the coupling was removed and installed on an alternator shaft. The purpose of the test is to ensure that the coupling's elastomer section, which was designed to slip in the event of an alternator shaft seizure, will not slip under normal conditions. However, it is possible for certain components within the coupling to shift slightly during this test. If they shift far enough, the coupling will not be properly seated when installed on the alternator shaft. This condition is not readily detectable by direct observation. There are currently no published procedures to inspect or measure the coupling for this out-of-tolerance condition. One engine overhaul facility found two new couplings as received from the manufacturer that were out of tolerance.

    The coupling could also have failed due to one or more of the following: insufficient torque applied to the alternator shaft nut, loosening of the nut to align the cotter pin holes, or failure to lubricate the threads before assembly on the shaft. Either an out-of-tolerance coupling or an improperly installed one can result in insufficient clamping force holding the coupling against the alternator. If there is insufficient clamping force, the coupling can rotate on the shaft and cause unusual wear and the ultimate failure of the coupling, which can lead to catastrophic engine failure.

    The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
    The total loss of engine power due to the failure of the alternator drive coupling. Contributing to the accident was the pilot's inability to locate and navigate to a suitable forced landing site due to low cloud ceilings.
     
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  6. Rushie

    Rushie Pattern Altitude

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    Thank you, Doc, I thought I remembered it had something to do with the alternator.
     
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  7. Clip4

    Clip4 Final Approach

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    First, it is possible for components of the coupling to progressively move out of tolerance due to repeated "slip testing," which is a procedure the engine manufacturer prescribed to be performed anytime the coupling was removed and installed on an alternator shaft. The purpose of the test is to ensure that the coupling's elastomer section, which was designed to slip in the event of an alternator shaft seizure, will not slip under normal conditions.

    Possibility #1. https://www.qaa.com/products/aircra...ve-couplings/646655-alternator-drive-coupling

    The coupling (a device for connecting parts of machinery) is not part of the alternator. It is an engine part.
     
    Last edited: Dec 4, 2019 at 5:41 PM
  8. Doc Holliday

    Doc Holliday Line Up and Wait

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    Really Cliffy?

    When was the last time you worked on, removed or installed one of these?

     
  9. Clip4

    Clip4 Final Approach

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    The Part is an engine part, not an alternator part.
     
  10. Doc Holliday

    Doc Holliday Line Up and Wait

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    Ok Cliffy. :rolleyes:
     
  11. Clip4

    Clip4 Final Approach

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  12. Rushie

    Rushie Pattern Altitude

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    Calm down. I changed the title to more accurately state what it was that was out of tolerance.
     
  13. Doc Holliday

    Doc Holliday Line Up and Wait

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    Appreciate it Rush. I knew exactly what you were referring to.
     
  14. Doc Holliday

    Doc Holliday Line Up and Wait

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  15. Rushie

    Rushie Pattern Altitude

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    Well what’s bothering me is I read that entire kathryn’s report including the whole part you quoted above about the alternator assembly and didn’t remember any of it, couldn’t even recall that the plane was a Bonanza. Maybe I’m coming down with Alzheimer’s. On the other hand I recently had a cog screen (medical exam for buying LTC insurance) where they told me ten words and then later asked me what they were and I remembered all ten of them, so go figure.:D
     
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  16. Omalley1537

    Omalley1537 Line Up and Wait

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    Were they “you should go buy another airplane as soon as possible?” I think even I could remember those ten words...:D
     
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  17. 3393RP

    3393RP Pattern Altitude

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    What's a bit sobering about the failure is that it can be induced by the test which verifies the slip arrangement works probably, and repeated performance of the test can derange the assembly in a manner that is "not readily detectable by direct observation" (NTSB report quoted).

    Can any A&Ps comment on this? Is it common knowledge that failure of the coupling can cause oil starvation and catastrophic failure of the engine? Does your work on the coupling command the attention it deserves? Thanks in advance for replies.
     
  18. Rushie

    Rushie Pattern Altitude

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    I hope an A&P comments too. That is what bothers me so much about this case. It’s a rare case where the pilot did absolutely nothing wrong. You could be the best pilot in the world and maintain your airplane perfectly and still have this happen, if it’s true that it’s “not readily detectable by direct observation”.