12/4/07 AC 25.1701-1
showing compliance with the specific provisions of § 25.1703 (a) through (d). Paragraph
5.b.(8) deals with EWIS component selection and paragraph 5.b.(9) has specific guidance
on wire selection. Paragraph 5.b.(10) discusses EWIS component selection for future
modifications.
(1) § 25.1703(a)(1). This section requires that each EWIS component be of a kind
and design appropriate to its intended function. In this context, the requirement means
that components must be qualified for airborne use, or otherwise specifically assessed as
acceptable for their intended use. To be “appropriate” means that the equipment is used
in a manner for which it was designed. For example, a wire rated at 150 degrees Celsius
would not be appropriate for installation if that installation would cause the wire to
operate at a temperature higher than 150 degrees Celsius. Wire and other components
made for household or consumer products use may not be appropriate for airborne use
because they are manufactured for the consumer market and not for use in an airborne
environment. Other factors that must be considered for EWIS component selection are
mechanical strength, voltage drop, required bend radius, and expected service life.
Refer to paragraph 5.b.(8)(a) for further explanation of “expected service life.”
(2) § 25.1703(a)(2). This section requires that EWIS components be installed
according to their limitations. As used here, limitations means the design and
installation requirements of the particular EWIS component. Examples of EWIS
component limitations are maximum operating temperature, degree of moisture
resistance, voltage drop, maximum current-carrying capability, and tensile strength.
EWIS component selection and installation design must take into account various
environmental factors including, but not limited to, vibration, temperature, moisture,
exposure to the elements or chemicals (de-icing fluid, for instance), insulation type, and
type of clamp. In addition, characteristics of both conductor and insulation for wires
and cables that are required to regularly flex, such as those in doors and hatches, should
also be considered when selecting them for such applications.
(3) § 25.1703(a)(3). This section requires that EWIS function properly when
installed. The key word in understanding the intent of this section is “properly,” as that
relates to airworthiness of the airplane. For an EWIS component to function properly
means that it must be capable of safely performing the function for which it was
designed. For example, the fact that an in-flight entertainment (IFE) system fails to
deliver satisfactory picture or sound quality is not what the term “properly” refers to, is
not a safety issue, and thus is not a certification issue. Failure of an EWIS component
has the potential for being a safety hazard whether it is part of a safety-related system or
an IFE system. Therefore, EWIS components must always function properly (safely)
when installed, no matter what system they are part of, and any malfunction of the
EWIS must not degrade the airworthiness of the airplane (refer to § 25.1705 for
terminology relating to failure classifications).
(4) § 25.1703(a)(4). This section requires that EWIS components be designed and
installed so mechanical strain is minimized. This means the EWIS installation must be
designed so that strain on wires would not be so great as to cause the wire or other
components to fail. This section requires that adequate consideration be given to
mechanical strain when selecting wire and cables, clamps, strain reliefs, stand-offs, and
5