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recommendations in case of new wiring installation after delivery to
the aircraft
8 April 19 2002 27
2.4 OEM Review design and maintenance practices regarding the use heat
shields. Establish on-condition criteria for the replacement of wire in
heat-damaged bundles (external and internal heat). Develop and
implement configuration management processes to prevent load
creep that may result in circuits operating near the rated capacity and
conductor heating
Boeing - Expected and actual sources of heat impinging on electrical
wiring is presently taken into consideration during the design of the
electrical system. Allowable wire damage criteria is presently
specified in the SWPM. Boeing presently provides electrical load
documents with the delivery of new airplanes and conducts electrical
load analysis on in-service airplanes upon request
Airbus - Expected and actual sources of heat affecting electrical
wiring is presently taken into consideration during the design of the
electrical system. Allowable wire damage criteria is presently
specified in the ESPM. Airbus presently provides electrical load
documents (ELA) with the delivery of new airplanes. Airbus supplies
the ELA in an electronic format to allow the operator to update the
actual electrical load of the aircraft following post delivery
modification of the aircraft
Lockheed - LMCO design practices have taken into consideration
wiring in proximity to heat sources. Allowable damage to wire is
specified in the SWPM. LMCO provided operators with a load
analysis at delivery. It is the responsibility of the operator to update
the analysis as require
[COMMENT 1 directed at Boeing] How do we reconcile the
inspection report finding that heat damaged wiring is relatively
common, with Boeing’s response that the manufacturer presently
takes into account the expected and actual sources of heat impinging
on wiring? Is it part of the design that wiring should be damaged by
heat? What is the long-term consequence of such a design
philosophy?
[COMMENT 2, also applies to 2.4/2.5 and 2c2] From the various
comments, I do not see an effort to include in the Task 6 report Part
25 Design guidelines that govern where heat shields/drip shields are
to be installed. While definition by each OEM as to where such
items are to be installed on a type certified airframe are provided
through the maintenance delivery documentation, there is nothing for
operators/STC agencies to use for after delivery changes to the
aircraft. Of concern are the various interior changes done by many
carriers that move galley and lavatories throughout the cabin. With
these interior changes, location of wiring, potable water, and waste
water lines are changing. I presently see no guidance coming that
instructs when to use heat shields/drip shields when an electrical
disconnect panel is now too close to the rerouted plumbing
components.
[COMMENT 3 directed at Boeing]
The recommendation was made because the Working Group
observed apparently heat damaged wire in areas near heat-emitting
surfaces and equipment. I have no doubt that Boeing did consider
heat sources when designing the electrical interconnect system. The
question is whether those considerations were sufficient and whether
their assumptions have stood the test of time.
8 April 19 2002 28
[COMMENT] Section 20-10-11 correctly sites vibration, heat, cold,
fuel, dirt, moisture, and hydraulic fluid as potential sources of
damage to wire. Section 20-10-13, however, discusses damage
assessment only in terms of traumatic damage. There is no
discussion on how to identify and correct thermal or chemical
degradation – the intent of this recommendation
OWNER REMARKS: OEM P3
In the case of heat impinging on wiring, protection is provided during
the initial design for known or locations where heat is expected.
Additional protection is provided in locations where in-service
experience dictates that protection is needed. For example,
Lockheed Martin requires the use of Bentley Harris type sleeving and
segregation from heat producing equipment to address known heat
sources. Operators are expected to identify areas of heat-damaged
wiring during normal maintenance activities and take appropriate
action. One appropriate action is to request that the OEM develop
and provide fleetwide protection if the damage is expected to occur
on other airplanes, or if the nature of the damage is considered to
impugn safety.
As far as post-delivery modifications are concerned, Airbus is
currently reviewing the ESPM content related to wire routing and
segregation and will include in the ESPM guidance and
　
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