Aircraft Maintenance: Engine control cable failures

And so, it always concerns me when I encounter an especially stiff or rough engine control that the owner hasn’t noticed during routine flying. As with many aircraft systems, we are often presented with warning signs before an ultimate failure occurs. In the case of engine control cables, these warning signs should be heeded as seriously as a binding elevator or aileron.

To better understand how engine control cables work (and how they fail), it’s first important to understand how they are constructed. By design, an engine control cable must provide the pilot with positive and precise control to push and pull the corresponding throttle, mixture, or prop lever on the engine. The cable must also be flexible enough to be routed from the cockpit through the firewall and around the engine. It must operate smoothly while including features to adjust the friction so that it moves when you want it to and stays put when you don’t. Finally, it must be durable to withstand the high-vibration and high-temperature environment of the engine compartment.

To accomplish these goals, most engine control cables are designed using a braided cable mated to solid, threaded rods at each end. The braided cable is housed within a flexible, spiral metal conduit with an anti-chafe liner between the conduit and cable. You don’t usually see the spiral metal conduit because it is covered in a black sleeve to keep out dust and contaminants. The conduit transitions to a rigid metal tube as it approaches the “business end” of the control at the engine where it houses the solid rod portion of the control. Since most control levers on the engine operate in an arc, this rigid tube is swaged to the flexible conduit with what is known as a “swivel fitting” so that the tube can angle up and down to follow the level arm movement.

I reached out to John Cowan, business development manager at McFarlane Aviation Products, to better understand the issues these cables encounter over time and how best to care for them. Cowan explained that most of the issues occur at bends in the control cable. When the cable housing makes a turn, pushing the control in will cause the braided cable inside to rub against the outside of the bend. Conversely, pulling on the cable will cause rubbing on the inside of the bend. The cable is designed for this.

This post was originally published by AOPA on . Please visit the original post to read the complete article.

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