Landing Gear Issues

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  • #84192

    Our 1978 421C had just gone through an annual. The left main was worked on to add shims that would compensate for wear. We took the plane up for a 2 hour cylinder break in flight and made one (smooth)landing. The next day I took it up once more to check out the avionics but when we landed there was a slight pull to the left. It corrected, then it happened, there was an aggressive pull to the left. I compensated with full right ailerons, and hard right break. She came to rest on the runway with the left main tire turned 90degrees to the runway. The bolt connecting the torque links was missing! We walked the entire length of the runway, no bolt. The mechanics that signed off on the annual said they remembered looking at the bolt, nut and cotter key so the only explanation is the bolt sheared from age. That is when I began checking and found out this has happened to other 400 series Cessna. Now I am wondering, if it is just the price of a “bolt”(approximately $6.00) that would prevent this possible catastrophic accident from happening, then WHY wouldn’t you just replace the “bolt” a each annual!!!!! Seems too logical to me.

    I hope this helps others from experiencing the same issue.

    #98675

    Thanks for sharing! Do you have a picture of the bolt or a part number?

    #98678

    Welcome to the Logical Club πŸ™

    You are not alone.

    #98682

    If that is the only time in your aircraft life that you look, think, and scratch your head as to why something was done or not done I’d say you are one of the luckiest pilots I know……..Just my opinion. I seem to have that distinct thought a lot!! Numerous times when I am looking at a plane for the first time. Apparently common sense isn’t factored into getting an a&p license. I’m not saying that none have common sense….just some…..

    #98685

    It was brought to my attention the other day that close tollerence AN bolts have a radius under the head of the the bolt and when torqued against the bushing of a drag link, excessive pre-load pressures can be placed on the head of the bolt and with a side load on the landing gear the bolt can pop it’s head off. The suggestion was to use a NAS close tollerence bolt in drag links as it has less of a radius under the head.

    #98688

    The bolt we are currently using is:
    AN175-20 with P/N 5045018-2 washer under the head

    I cannot tell you if that is the same as the bolt that was in there because it was never found.

    #98689

    Thanks! This is the bolt on the landing gear side of the piston for retract and extension? Have they checked the bolt on the other side?

    Were there any markings of wear in the bolt hole?

    Eric

    #98694

    The bolt hole did not show signs of wear. I had them change the bolt in the right side AND nose. This is something I am going to have done at each annual which is probably overkill, but I don’t ever want that to happen again. Besides it spoils a perfect landing πŸ˜‰

    #98703
    rwelsh
    Participant

      Well, I can tell you THAT THERE IS HARDLY ANY LOAD ON THE SCISSOR BOLT. The weight of the wheel and strut (about 20 pounds) hangs on the bolt with the gear hanging down before retraction and during the extended time, but that 5/16″ bolts is stressed to 11,000 plus pounds in shear. They do wear slightly over time, but nothing near enough to have the bolt shear. You might get a shimmy if the bolt was worn, but I can’t see it shearing. My take is they shimmed the scissors and forgot to put the cotter pin in the castle nut. But they gave you a good story, but I don’t think it would hold water.

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