Recommendation

Interim response:

We are investigating the issue, considering the scope of
the recommendation and planning the best course of action. We
anticipate submitting a follow-on response updating our progress by
31 March 2012.

The Australian Transport Safety Bureau (ATSB) is satisfied that
there is sufficient airworthiness regulation and guidance relating
to electronic wiring interconnection systems (EWIS), and notes that
the advised safety action should further improve the level of risk
regarding EWIS.

However, EWIS is not the subject of the ATSB recommendation,
insofar as it is defined in FAR § 25.1701 and clarified by the
final rule for the Enhanced Airworthiness Program for Airplane
Systems/Fuel Tank Safety (EAPAS/FTS) as follows: 'the EWIS
certification and operational requirements in the final rule apply
to wires that 'interconnect' airplane systems, as opposed to wiring
located solely within the enclosure of a piece of avionics
equipment, for example.'

The ATSB recommendation is intended to address the protection of
non-EWIS electrical and electronic components, that is; avionics
equipment such as line-replaceable units (LRUs). Such components
are not required to be protected to a similar degree as EWIS; the
only requirement being, that 'critical environmental conditions
must be considered' [FAR § 25.1309 (e)]. The ATSB considers that,
like EWIS, other parts of the avionics systems comprise
off-the-shelf components which are uniquely installed and are
subject to different environmental conditions in each aircraft
type. For example, on some aircraft models the electronics bay is
located directly underneath a galley, presenting an increased risk
of water ingress. A component installed in that aircraft presents a
completely different risk to the same component fitted in a
different aircraft. The ATSB concern is that aircraft-specific
environmental risks need to be considered separately for each LRU
or avionics component.

As Part of the Enhanced Airworthiness Program for Airplane
Systems / Fuel Tank Safety (EAPAS/FTS) rulemaking and guidance
project, the FAA developed and implemented several enhancements
including aircraft wiring practice training for the engineers and
inspectors and an internet-based comprehensive airplane job aid.
The job aid includes information regarding installation, interfaces
between wiring and equipment, and protections against foreseeable
physical and functional faults.

The EAPAS/FTS rule contains new certification and operational
requirements to mitigate aging issues in aircraft wiring and
associated components for the current and future fleet of
aircraft.

The EAPAS rule includes:

• Requirements that Electrical Wire Interconnection System (EWIS)
  components be selected so that they are fit for purpose and
  appropriate for the environment in which they will be used,
  including requirements to address known characteristics of the wire
  such as arc tracking.
• EWIS identification requirements for clear and consistent
  methods of wire component identification for such things as
  function, separation requirements, and design limitations.
• Requirements that access be provided to allow inspection and
  replacement of EWIS components necessary to maintain the continued
  airworthiness, including the integrity of the required drip
  shields, of the airplane.
• Enhanced EWIS maintenance and inspection requirements,
  including mandatory replacement of EWIS components as
  necessary.

The FAA issued accompanying Advisory Circulars (AC) with
guidance on complying with the enhanced requirements. The AC
provides guidance for developing an enhanced EWIS training program
at operator and maintenance facilities which supplements internal
FAA training. The objective of the comprehensive training program
is to give operators, maintenance, and repair organizations a model
for developing their own EWIS training program. The curriculum
outlined in the AC ensures that proper processes, procedures,
methods, techniques, and practices are used when performing
maintenance, preventive maintenance, inspection, alteration,
repair, and cleaning of EWIS.

We determined that current Title 14, Code of Federal Regulations
(14 CFR) part 25 regulations, with the requirements added by the
EAPAS/FTS rule, are adequate with respect to liquid contamination
of electrical components. We are reviewing the related guidance
material to determine if there are additional ways it might be
improved to better address the issue.

We understand that the ATSB's concerns are not limited to
Electrical Wire Interconnection System (EWIS) components but are
directed at all electrical and avionics equipment in a broader
sense.  The broader concerns are adequately addressed in our
current regulations and policy governing both component-level
qualification (Technical Standards Orders and guidance material
such as DO-160, Environmental Conditions and Test Procedures for
Airborne Equipment) and higher-level, aircraft installation
requirements (such as 14 CFR 25.1309).

In highlighting the FAA's more recent Enhanced Airworthiness
Program for Airplane Systems / Fuel Tank Safety (EAPAS/FTS)
rulemaking in our previous response, we pointed out that many of
those improvements also inherently address non-EWIS components.
Enhanced Zonal Analysis, periodic cleaning/inspection, and
monitoring of the protective features such as drip shields, are
some of the examples of the enhancements which have a positive
impact on the conditions in which all electrical and electronic
components are installed and operating.

In conclusion, our current component-level qualification
standards and current 14 CFR Part 25 regulations, with the added
requirements of the EAPAS/FTS rule, are adequate with respect to
liquid contamination of electrical and electronic components. 
We will continue to review related guidance material to determine
if there are additional developments to further enhance the
protection of installed electrical and electronic components.

We believe we have effectively addressed the ATSB's concerns and
consider our actions complete with regard to FAA Safety
Recommendation 10.359.