Frozen throttle cable

Discussion in 'Maintenance Bay' started by Matthew Rogers, Dec 7, 2018 at 6:23 PM.

  1. Matthew Rogers

    Matthew Rogers Pre-Flight

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    I have a frozen throttle cable in my 150f. I know it is water because I have flown a few times, first having to thaw it out. It went from totally stuck to moving after application of heat.

    Today I attempted to blow out the water by injecting from the inside end, but the cable is sealed too well to get anything meaningful into the cable housing from the inside. Is there any more access at the throttle body end of the cable to blow air or some lubricant through the housing to remove the water? I have to remove the cowling to access that end.

    Does anyone have an idea of how to get water out of a 150 throttle cable without removing and reinstalling the cable? Should I just go get a whole new cable assembly for $170 and assume that this one is corroded as well from the liquid inside?
     
  2. Dan Thomas

    Dan Thomas En-Route

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    Why would you go flying with water in the cable at temperatures where it might freeze in flight and disable that control?

    The water got in there somehow. The plastic sheath on the cable housing is likely split somewhere and water is seeping into it. Better to replace it. The wire is probably corroded anyway, and rusty music wire breaks easily.

    How many hours on that control? We had one break in flight in a 150. A student and instructor were practing spins, and the instructor had the student enter a power-on stall and let it roll into the spin. He told the student to pull the throttle out as the airplane rolled, and the student did. Pulled the knob and shaft right out. The wire had broken off just past the end of the shaft. The instructor recovered from the spin and they set up for a forced landing, since the engine was at idle. Then the instructor took the knob and shaft and pushed it back into the hole, and it pushed the wire forward and the power came back. They flew back that way and cut the mixture on final.

    Had carb heat control cables break, too. Once I became responsible for the maintenance there I made it a policy to replace all engine controls when the engine was replaced. I have seen some pretty bad controls, just ready to fail. And I've seen the wrong controls in airplanes, too. I've found controls almost seized due to age and sludging up of the lubricants in them. Found them corroded. It's false economy to keep using defective critical control parts like that.
     
  3. IK04

    IK04 Pre-Flight

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    Just get a new cable/knob. Sounds like it's time...
     
  4. Matthew Rogers

    Matthew Rogers Pre-Flight

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    Well, I was pretty sure that the cable was frozen inside the cockpit side as I pre-heated the engine using forced hot air for a long time and everything was toasty warm inside the cowling (with a blanket over top and plugs in as well), but the cockpit was still cold. Once the engine started, I had the cockpit heater on full and that kept the entire assembly well above temp.

    But it makes sense to just replace the entire unit and that solves both old parts, potential corrosion, and the freezing in one go.
     
  5. alfadog

    alfadog En-Route

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    I would replace the cable but that said, you can use the old motorcycle trick to get oil in the cable and displace the water.
     
  6. Matthew Rogers

    Matthew Rogers Pre-Flight

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    Well, in defense of the cable - we had the wettest fall on record here since 1865! Nothing like it in recorded history and the plane is tied down outside with a slightly leaky window. It only takes the smallest amount of water inside a cable housing to freeze the cable solid. Sometime over the past several months, a tiny amount of water vapor entered the housing, condensed overnight (perhaps repeated a hundred times with the hundred days of rain this year), and built up to form a single liquid water droplet! That is all it takes. The the water is not in the "throttle body", but the cable housing. The throttle body lever works smoothly, just the cable is freezing up in the cold weather overnight.

    New cable ordered.
     
  7. Stewartb

    Stewartb Final Approach

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    What type of preheat? You said forced hot air. is it propane? Propane makes water vapor and it condense in all sorts of places that are cold. Maybe the preheat is the problem?
     
  8. Matthew Rogers

    Matthew Rogers Pre-Flight

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    It was propane, but the throttle was first discovered frozen in the really cold snap at Thanksgiving. We did not preheat at all before that time so the preheat did not cause it.
     
  9. Plano Pilot

    Plano Pilot Pre-takeoff checklist

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    How would he know water was in the cable if it was working for departure?
     
  10. Matthew Rogers

    Matthew Rogers Pre-Flight

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    Because it was frozen solid before and during the first part of warming up the airplane. But that leads to the question of how one would know if their throttle cable had water in it if they started a flight at 34 degrees and flew north for a few hours into a colder temperature and also at high altitude. You would have no prior warning because everything was fine on departure. I believe that in my case there is plenty of warm air inside the cowling during flight and warm air inside the cabin to prevent any freezing during operation. Judicious use of the throttle also keeps it moving freely. But again, I ordered a new one and should be good by next week.
     
  11. JAWS

    JAWS Line Up and Wait

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    Good decision. :)
     
  12. Dan Thomas

    Dan Thomas En-Route

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    When the old one comes out, look at the area that passes through the firewall. It chafes against the firewall pass-through, which was only a metal doubler in a lot of those older airplanes, and there was supposed to be a steel outer chafe sleeve crimped over the housing to take the chafing. On a lot of cables the sleeve was not well-placed and the PVC housing cover would get rubbed off. Any water that leaked though the gap between the fuselage and upper cowling could run down the firewall and get into the cable assembly though that unprotected section.

    I've found the wrong cables in airplanes, too. Saving money at any cost.
     
  13. Arrow115

    Arrow115 Pre-takeoff checklist

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    I would just replace the cable. I have had 2 inflight throttle cable failures on 2 different aircraft. It’s not worth trying to stretch out the service life on those cables.
     
    SCCutler likes this.
  14. Lee Burgin

    Lee Burgin Filing Flight Plan

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    I would bet it is not water. Lube gums up over a long period of time. Just for giggles, take the cable out (you already said you have a new one coming) and soak it in mineral spirits or naphtha over night. The lube it with synthetic oil. You will have a great spare.
     
  15. Matthew Rogers

    Matthew Rogers Pre-Flight

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    I have to disagree that it is not water. It went from smooth (or at least smooth for an old cable), to totally stuck on the first really cold day of the year. Once warmed up, it went from totally stuck to moving the instant it melted. I was in the aircraft checking and waiting for it and it was like - stuck, stuck, stuck, stuck, free moving.

    I will certainly inspect the cable when it is removed, but it works freely when it is not below freezing or when pre-heated. I just flew on Sunday in the afternoon when the temps were above freezing (35) and did not have to preheat the airplane or throttle cable.