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Hours of Vibration Conditioning 30
34 Group IIM Testing: XLETFE (Wire Code 4) Wire Damage After 250 Hours of
Vibration Conditioning 30
35 Group IIM Testing: PTFE, Mineral-Filled (Wire Code 7) Wire Damage After
250 Hours of Vibration Conditioning 31
36 Group IIM Testing: PTFE/Glass Braid (Wire Code 9) Wire Damage After 250
Hours of Vibration Conditioning 31
viii
37 Group IIM Testing: PI/PTFE (Wire Code 10) Wire Damage After 250 Hours of
Vibration Conditioning 32
38 Group IIM Testing: PI/PTFE, Alloy (Wire Code 11) Wire Damage After 250
Hours of Vibration Conditioning 32
39 Wire Interactions in Group IIM Mixed Bundles 34
40 Moderate Wire-to-Wire Wear on XPI in Nonmixed Group IIM Bundle 34
41 Severe Wear on PI/PTFE From Clamp When Mixed With XPI in Group IIF 35
42 Group IIF: Tightness of Clamp vs Wear From Wire 36
43 Group IIF: Tightness of Clamp vs Wire Wear From Clamp 36
44 Severe Wear of PTFE/Glass Wire From Clamp in Group IIM Nonmixed Bundle 37
45 Group IIM: Tightness of Clamp vs Wear From Wire 37
46 Group IIM: Tightness of Clamp vs Wire Wear From Clamp 38
47 Moderate Wear of XPI and PI/PTFE From Strap in Group IIF 39
48 Moderate Wear of PI/PTFE From Strap When Mixed With MF-PTFE in
Group IIF 39
49 Moderate Wear on PI From Lacing String When Mixed With MF-PTFE in
Group IIF 40
50 MF-PTFE Wire Damaged From PI Wire in the 80-Pound Crush Test 42
51 PI/PTFE Alloy Wire Damaged From PI/PTFE Wire in the 80-Pound Crush Test 42
52 XLETFE Wire Damaged by PI Wire in the 120-Pound Crush Test 42
53 PI/PTFE Alloy Wire Damaged by Same Wire Type in the 120-Pound Crush Test 42
ix
LIST OF TABLES
Table Page
1 Wire Types Evaluated 7
2 Wire Combinations Tested in Group I 8
3 Wire Combinations Tested in Group II 9
x
LIST OF ACRONYMS
AC Advisory Circular
CFR Code of Federal Regulations
DWV Dielectric withstand voltage
EWIS Electrical wiring interconnect system
FAA Federal Aviation Administration
IR Insulation resistance
NAC Naval Avionic Center
OAM Original aircraft manufacturer
PI Polyimide
PTFE Polytetrafluoroethylene
PVC Polyvinylchloride
XLETFE Cross-linked ethylene-tetrafluoroethylene
XPI Cross-linked polyalkene-imide
xi/xii
EXECUTIVE SUMMARY
Original aircraft manufacturers have designed and built aircraft with various wire types. This
occurred because the technology, materials, and processing of wire has continually improved.
New aircraft may have multiple wire types in the same aircraft to meet various environmental
zone requirements. Wiring sections may be modified or rewired with the same wire that was
originally installed in the aircraft or with a newer, more advanced wire, thus mixing wire types in
bundles. Little data has been generated and published indicating whether mixing wire types
creates problems with the long-term integrity of the electrical wiring.
An assessment of the past and current guidelines regarding the presence of multiple wire types
was performed. Conclusions were made regarding the effects of multiple wire types mixed
together in the electrical wiring interconnect system (EWIS), based on test results, and
recommendations are made regarding the mixing of multiple wire types within the EWIS during
design, repair, and maintenance of the EWIS.
None of the documents reviewed specifically addressed or restricted mixing of dissimilar wire
types in bundles, but regulations stipulated that the wires selected must meet the environmental,
application, interface, and design requirements.
Accelerated vibration testing of mixed and nonmixed wire bundles was performed both with and
without hydraulic fluid and metal shavings contamination. The results indicated that none of the
ten wire types tested exhibited accelerated wear characteristics in mixed bundles compared to
nonmixed bundles. No electrical failures were attributed to mixing of wire types within a bundle
during laboratory testing. Many of the wire types, however, exhibited significant wear from
clamps and structure in both the contaminated and uncontaminated conditions.
Routine inspections of all wire types should continue in aging aircraft to ensure that the electrical
wire maintains physical and electrical integrity and to monitor the wire for signs of wear from
wires, clamps, and the aircraft structure. Inspection of the clamped areas should be emphasized,
with the clamp to wire tightness being evaluated.
xiii/xiv
1. INTRODUCTION.
1.1 PURPOSE.
The purpose of this study was to determine the effects of mixing wire types in aged aircraft and
to develop Federal Aviation Administration Advisory Circular (AC) or regulation
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