airframe vibration.

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  • #83668

    I recently experienced sudden vibration in cruise flight which seemed to be coming from the horizontal stabilizer. It finally stopped after I cycled the boots several times. After landing, my mechanic and I checked the trim tab and elevator finding no abnormal play or looseness .Cessna recommends the trim tab actuator be removed and calibrated every 500 hrs or 3 years. Mine was beyond this time so we removed it and found it was worn significantly beyond service limits. It is now out for overhaul. Apparently wiggling it on annuals doesn`t duplicate the dynamic loads experienced in flight. I also found that the first 340 built crashed and killed the Cessna test pilot on its first flight in 1970 after a horizontal stabilizer trim tab malfunction. Cessna,Wings for the World. by William Thompson.

    #95438

    If I remember correctly the nut came off and the bolt departed. The result was flutter and that was the end. That is why the bolt connecting the trim tab to the control shaft has or should have a cotter pin inserted to prevent the nut from backing off. If it doesn’t, change the nut before the next flight.

    #95446

    Good find, thanks for sharing. Glad you are safe! Did you take pictures?

    #95614

    My air frame vibration problem was resolved by replacing the elevator trim tab actuator with an overhauled one. Test flight up to Vne was uneventful.

    #95616
    cochrane
    Participant

      From what I recall, past publications regarding recommended overhaul intervals for the actuator have conflicted with Cessna’s recommendations. Since you rarely hear of any actual problem reports I have put that overhaul in the ‘not necessary right now’ category. Sounds like a wise preventive measure.

      How many hours did your actuator have on it and who overhauled yours?

      One other item related to the actuator that is worth mentioning is the attachment screws on the trim tab. I don’t recall whether it was a SB or not but some of the screws have rusted /broken and should be replaced or checked.

      Thanks for posting.

      Geoff

      #95632

      My elevator trim tab actuator had about 800 hrs and 10 years time in service.The plane has had good maintenence by several reputable shops during this time. The tail vibration was the most unsettling experience I`ve had in 50 years of military and private flight operations. I contacted the parts dept.at TAS aviation for advice. He did not have an actuator in stock but called me back with several options. Cessna had one in stock for $4900,a firm in Kansas could potentially overhaul my unit for about $600 in about 2 weeks or I could buy an overhauled unit from L&M Aircraft Parts in Wichita KS for $965. I chose the L&M option (316 946 0500 ). The part was shipped promptly and my plane was airworthy in 2 days. I don`t know yet whether I`ll be liable for a $2000 core charge.

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