AMC to Appendix H, H25.5 Instructions for Continued Airworthiness applicable to EWIS

ED Decision 2008/006/R

In accordance with subparagraph H25.5 the applicant must prepare Instructions for Continued Airworthiness (ICA) applicable to EWIS as defined by 25.1701 that should include the following:

1       Maintenance and inspection requirements for the EWIS developed with the use of an enhanced zonal analysis procedure (EZAP) that includes:

a.       Identification of each zone of the aeroplane.

b.       Identification of each zone that contains EWIS.

c.       Identification of each zone containing EWIS that also contains combustible materials.

d.       Identification of each zone in which EWIS is in close proximity to both primary and back-up hydraulic, mechanical, or electrical flight controls and lines.

e.       Identification of -

—         Tasks, and the intervals for performing those tasks, that will reduce the likelihood of ignition sources and accumulation of combustible material, and

—         Procedures, and the intervals for performing those procedures, that will effectively clean the EWIS components of combustible material if there is not an effective task to reduce the likelihood of combustible material accumulation.

f.       Instructions for protections and caution information that will minimize contamination and accidental damage to EWIS, as applicable, during the performance of maintenance, alteration, or repairs.

2       Acceptable EWIS maintenance practices in a standard format:

Applicants should document EWIS maintenance practices in a standard format. This is typically accomplished with publication of a standard wiring practices manual (SWPM). The rule is not intended to require that every manufacturer’s SWPM is identical. The intent is to enable people performing EWIS maintenance and repairs to find information in the SWPM more quickly and easily, regardless of what aeroplane model they are currently working on. Standard wiring practices include procedures and practices for the installation, repair, and removal of EWIS components, including information about wire splices, methods of bundle attachment, connectors and electrical terminal connections, bonding, and grounding. A SWPM is not a design manual, and designers of EWIS modifications for specific aeroplane models should not use it as such. But it does provide the designer with insight into the types of EWIS components used by the TC holder and the procedures recommended by the manufacturer for maintenance or repair that supports continued airworthiness of the components. AMC 20-23 “Development of Standard Wiring Practices Documentation,” provides guidance on how to comply.

3       Wire separation requirements as determined under 25.1707:

Applicants should include EWIS separation requirements in the ICA. EWIS separation guidelines are important for maintaining the safe operation of the aeroplane. Maintenance personnel need to be aware of the type certificate holder’s separation requirements so they do not compromise separation in previously certified systems.

Determination of EWIS separation requirements is required by 25.1707. To comply with H25.5, the applicant should develop a way to convey these separation requirements and place them in the ICA. For example, if an aeroplane has a fly-by-wire flight control system and a minimum of 2 inches of physical separation is needed between the EWIS associated with the flight control system and other EWIS, this information should be available in the ICA.

Similarly, the separation of certain wires in fuel tank systems may be critical design configuration control items and therefore qualify as an airworthiness limitation. Maintenance personnel need these guidelines and limitations because many times wire bundles must be moved or removed to perform maintenance.

The separation data included in the ICA can take many forms. If a particular aeroplane model has fly-by-wire flight controls, the manufacturer may designate the EWIS associated with the flight control systems by a certain identification scheme (as required by 25.1711), and in the ICA state that EWIS so designated must be maintained with XX amount of separation from all other EWIS and YY amount of separation from other aeroplane systems and structure. The manufacturer can then repeat this information for other EWIS associated with other aeroplane systems. The ICA could indicate how EWIS associated with IFE and other passenger convenience systems is identified, and that this EWIS must be maintained XX inches from other categories of EWIS or structure.

It is not the intent of the regulation to require a type design holder or an applicant to divulge proprietary information in order to comply. Certain information, however, needs to be made available to modifiers and maintainers to ensure that future modifications and repairs do not invalidate previously certified designs.

4       Information explaining the EWIS identification method and requirements for identifying any changes to EWIS under CS 25.1711. This paragraph requires that the ICA contain information explaining the EWIS identification method and requirements for identifying any changes to EWIS. This requirement is intended to ensure that future modifications that add EWIS, identify the added EWIS with the same type of identification scheme used by the original aeroplane manufacturer. This information will help modification designers and modification personnel avoid improper modification and repair of existing EWIS or improper installation of new EWIS. These personnel need to review the applicable standard wiring practices, EWIS identification requirements, and electrical load data for the aeroplane they are modifying.

5       Electrical load data and instructions for updating that data. The ICA should contain electrical load data and instructions for updating that data. Electrical load data and the instructions for updating that data are necessary to help ensure that future modifications or additions of equipment that consume electrical power do not exceed the generating capacity of the onboard electrical generation and distribution system.  Maintaining a record of actual airplane electrical loads is important to ensure that modifications to the original design do not impose electrical loads on the electrical generating system in excess of the system’s capability to provide the necessary power and maintain necessary margins. To comply with the requirements of this paragraph applicants need to provide:

a.       Electrical generating capacity of each source of normal electrical power generation.

b.       Electrical generating capacity of each source of emergency power generation.

c.       Electrical load capacity of each of electrical bus.

d.       Actual electrical loading of each electrical bus.

6       The ICA must be in the form of a document appropriate for the information to be provided, and they must be easily recognizable as EWIS ICA.

[Amdt 25/5]