Damage Assessment under FAA 25.1707(a)
FAA 25.1707(a) requires every EWIS to be designed and installed with adequate physical separation — by distance or an equivalent barrier — from other EWIS and aircraft systems, so a single component failure cannot create a hazardous condition. Compliance is shown through physical testing, simulation, or both.
“Each EWIS must be designed and installed with adequate physical separation from other EWIS and airplane systems so that a EWIS component failure will not create a hazardous condition. Unless otherwise stated, for the purposes of this section, adequate physical separation must be achieved by separation distance or by a barrier that provides protection equivalent to that separation distance.”
The regulation does not define a single fixed separation distance. Acceptable separation is determined by assessing what a credible EWIS failure — most often electrical arcing — would do to surrounding systems, and demonstrating that the design either prevents damage or contains it below a hazardous threshold.
Two compliance paths are available. Physical testing sets the system parameters (operating temperature, fluid pressure limits, minimum tube thickness) and a safety threshold, then exercises the configuration under arcing conditions. Simulation can complement physical testing or stand alone, and is particularly useful for sweeping across materials such as aluminum versus composite tube structures.
When test results sit near a failure condition without actually failing, the safety margin is unproven. Additional testing, an increased separation distance, or a protective barrier must follow. Lectromec's Arc Damage Modeling Tool (ADMT) is one accepted approach for simulating wire failures and the resulting damage to nearby harnesses, structure, and fuel or hydraulic lines, and has been used inside aerospace certification packages.
Inspectors and DERs look for a quantified safety margin, not a default distance. If the configuration in question has only ever been validated visually or against AS50881's default 0.5″ guidance, the certification basis is fragile. A documented arc-damage assessment — physical or simulated — converts that visual inspection into evidence that survives scrutiny.
Frequently asked
What separation distance does FAA 25.1707(a) require?
The regulation does not specify a fixed distance. It requires adequate physical separation — measured by distance or equivalent barrier — such that an EWIS component failure cannot create a hazardous condition. The acceptable distance is established by a damage assessment specific to the installation.
Can 25.1707(a) compliance be shown by analysis alone?
Yes. Simulation, including arc-damage modeling, is an accepted compliance path. Analysis is most defensible when paired with at least one anchoring physical test or when the simulation tool itself has prior certification precedent.
What counts as a 'barrier' under 25.1707(a)?
Any physical element — a shroud, conduit, fire sleeve, structural panel — that provides protection equivalent to the separation distance the design would otherwise require. The barrier's equivalence must be substantiated, not assumed.