control surface cable wearout - macro pic of worn cable

[RFguy]

Control cables really do wear out. (steel)

The macro lens of modern smartphone is rather useful for this :

More closely investigating a rather shiny cable where is runs with considerable tension under the pulley, 

one broken strand. Can be felt with finger. Replaced.

One might think 1 of of 49 (63?) strands is no big deal, but reading AC43, and closer inspection reveals the flattening wear of the cable (making for shiny appearance) is the cable strands being worn down and thinned under the pulley pressure... and eventually one lets go. 

Given that a lot of them are simultaneously worn down and thinned, a whole lot might let go shortly.... You could probably fly on this for another year (or 5) with before every flight inspection , but given that cables are in stock locally, it should be replaced. Document AC43  provides guidance on this, as usual . (replace it) . Lots of airplane maintenance stuff is annoying and painful, but ultimately these annoying things, will save your arse.

 

Edited September 19 by RFguy

[RFguy]

further.... think of the length of the region of flattening (usually in middle 20mm I think ) , this covers all the strand  bundles because of the helical wind... IE you are getting flattening in all the bundles and a high proportion of all the wire in each bundle- this is not simply isolated broken weak strand. 

It will be interested to do a load test on this cable, see how far it is above the normal tension that it lets go. In radio masts, we'd use this size guy cable for about 500kg working.

[onetrack]

As a matter of interest (and I have substantial experience in using Steel Wire Rope - or SWR as it's known), with regard to the safety angle, when using SWR in areas where safety is a priority (such as cranes and other lifting devices), the recommendation is that when easily visible flattening of the outer strands is apparent over more than 10% of the outer wires of the SWR, it's time to replace the SWR.

 

There are various levels of recommendations for safety limits for SWR, with Maritime use the lowest level, and mining and craneage use, applying substantially more strict levels of wear. Aircraft use requires a strict level of wear tolerance.

[RFguy]

A few days later.....Pull-Pull cable control airplanes. mutter mutter .. Well I can very much appreciate the simplicity of the jabiru with its pair of push-pull teleflex cables.....as sloppy as it is.

Edited September 24 by RFguy