Control Cable Separation under FAA 25.1707(i)
FAA 25.1707(i) requires EWIS to be separated from flight and other mechanical control cables so that chafing, jamming, or component failure of either cannot create a hazardous condition. Critical clamp markers, jam-prevention clamping, and Common Cause Analysis are the primary design controls.
“EWIS must be designed and installed with adequate physical separation between the EWIS and flight or other mechanical control systems cables and associated system components, so that: (1) Chafing, jamming, or other interference are prevented. (2) An EWIS component failure will not create a hazardous condition. (3) Failure of any flight or other mechanical control systems cables or systems components will not damage the EWIS and create a hazardous condition.”
Moving control cables present a distinct failure mode: they can abrade through harness insulation quickly. The result is one of three credible hazards — electrical arcing damaging or destroying every wire in the cable, loss of functionality on a flight-control cable, or arc-plume and molten-material damage to nearby systems.
Critical clamp markers are widely used in EWIS installations near control cables. A clamp marker is a visual indicator on the harness that tells a maintenance technician where a clamp belongs; the ideal pattern is a 50/50 marker split on each side of the clamp. Markers are not required by the regulation, but they materially reduce the risk that a harness shifts under maintenance and ends up where the design assessment did not place it.
Clamping density must prevent both chafe and jamming. A harness slack enough to contact a moving control cable, or a single missing clamp that allows the harness to droop into a pulley, is a hazardous condition. Inspection of clamp condition belongs in the ICA and the Enhanced Zonal Analysis Program. Common Cause Analysis must close the loop: the loss of a single mechanical cable cannot be allowed to damage an EWIS component supporting a redundant system.
Most control-cable findings are not design issues — they are maintenance drift. The harness was installed correctly, then drifted under access work, and no marker existed to tell the next technician where it should sit. Treating clamp markers and clamp density as cert deliverables, not nice-to-haves, closes that exposure.
Frequently asked
What is a critical clamp marker?
A visual indicator on an EWIS harness — typically a 50/50 marker split on each side of a clamp — that tells maintenance technicians where the clamp belongs. It is not required by 25.1707(i), but it is widely recommended for harnesses routed near mechanical control cables.
Does 25.1707(i) require Common Cause Analysis?
Yes, in effect. The regulation requires that failure of a control cable cannot damage an EWIS component that supports a hazardous condition. Demonstrating that property typically requires a Common Cause Analysis showing the failure paths do not converge.