Appropriately Stressed Out: Tension and Your Control Cables

Just about every General Aviation airplane flying today does so with the assistance of specifically loaded cables — when was the last time that yours were checked? Your cables are connected to your control yoke or stick (and your rudder pedals) and transmit the force from your hands, arms and feet to the control surfaces, where these forces cause the plane to climb, descend and do all the other things we command it to do.

Cables installed in airplanes aren’t just laid in the airframe. Instead, cables are typically placed under a specific amount of tension. The tension that is applied depends on the cable and its use — as well as the temperature. With the proper setup, cables should last for years in your plane without adjustment. But…

The Set Up
Take a look at your logbooks and look for an entry for the last time your cable tensions were checked, much less set. If you are like most pilots, you will notice that your cable tension isn’t routinely checked, unless you ask for it to be.

After years of service (including flying in turbulence and hard landings), your cables have lost some of their tension. This means that instead of responding to your control inputs as soon as you make them, you may have to pull or turn a little more, to get the slack out of the cables. Worst case: A cable that has been grossly neglected can actually jump the pulley and jam.

On the other hand, too much tension on the cables can cause different problems. The pulleys that the cables move over are typically made of fiberglass or composite materials. Placing too much tension on the cables can cause them to grind through the pulleys, which can cause binding between the pulleys and the cables. This binding translates to sticky or jerky control inputs, which translates to an unpleasant ride.

Keeping an eye on your cables from the cockpit isn’t easy, but there are some things you can do. First, listen for problems. Cycle through the full range of your flight controls’ available motion and listen for noises. If you hear anything that sounds like a scrape, have it checked out by a qualified mechanic. If you have not had your cable tension checked in a few years, ask your FBO to check it as part of your next annual.

Finally, don’t be afraid to ask your FBO about what they check during an annual inspection on your airplane. Are the pulleys lubricated? Have they been rotated to help them wear evenly? Are the cable tensions checked as recommended by the Service Manual, and at the correct frequency? Knowing about your cables, along with asking these key questions can help keep your cables doing what they are supposed to do, and not causing you problems while you are in flight!