ASTM F2799-14(2019)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F2799 − 14 (Reapproved 2019)
Standard Practice for
Maintenance of Aircraft Electrical Wiring Systems
This standard is issued under the fixed designation F2799; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.1 Definition—This practice defines acceptable practices
Barriers to Trade (TBT) Committee.
and processes for the maintenance, preventative maintenance,
and repair of electric systems in general aviation aircraft. This
2. Referenced Documents
practice does not change or create any additional regulatory
2.1 ASTM Standards:
requirements nor does it authorize changes in or permit
F2490 Guide for Aircraft Electrical Load and Power Source
deviations from existing regulatory requirements.
Capacity Analysis
1.2 Applicability—The guidance provided in this practice is
F2639 Practice for Design, Alteration, and Certification of
directed to air carriers, air operators, maintenance providers,
Aircraft Electrical Wiring Systems
repair stations, and anyone performing maintenance or repairs.
2.2 ICAO Standard:
1.3 Protections and Warnings—This practice provides guid-
ICAOAnnex 5 Units of Measurement to Be Used inAir and
ance to minimize contamination and accidental damage to
Ground Operations
electrical wiring interconnection systems (EWIS) while work-
2.3 JEDEC Standard:
ing on aircraft.
EIA 471 Symbol and Label for Electrostatic Sensitive De-
vices
1.4 “Protect and Clean As You Go” Philosophy—This
philosophy is applied to aircraft wiring through inclusion in
2.4 NEMA Standard:
operators’maintenanceandtrainingprograms.Thisphilosophy WC 27500 Standards for Aerospace and Industrial Electric
stresses the importance of protective measures when working
Cable
on or around wire bundles and connectors. It stresses how
2.5 RTCA Standard:
important it is to protect EWIS during structural repairs, (STC)
DO-160C Environmental Conditions and Test Procedures
installations, or other alterations by ensuring that metal
for Airborne Equipment
shavings, debris, and contamination resulting from such work
2.6 SAE Standards:
are removed.
AS4372 Performance Requirements for Wire, Electric, Insu-
lated Copper or Copper Alloy
1.5 Units—The values stated in inch-pound units are to be
regarded as standard. The values given in parentheses are AS4373 Test Methods for Insulated Electric Wire
AS21919 Clamp, Loop Type, Cushioned Support
mathematical conversions to SI units that are provided for
information only and are not considered standard. AS22759 Wire, Electrical, Fluoropolymer-Insulated, Copper
NOTE 1—When SI units are required, refer to Annex 5 of ICAO. or Copper Alloy
AS50881 Wiring Aerospace Vehicle
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
priate safety, health, and environmental practices and deter-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
mine the applicability of regulatory limitations prior to use.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1.7 This international standard was developed in accor-
Available from International Civil Aviation Organization (ICAO), Customer
dance with internationally recognized principles on standard-
Services Unit, 999 Robert-Bourassa Boulevard, Montréal, Québec, H3C 5H7,
ization established in the Decision on Principles for the
Canada, https://www.icao.int.
Available from the JEDEC Solid State Technology Association, 3103 N. 10th
St., Suite 240-S, Arlington, VA 22201-2107, https://www.jedec.org/.
1 5
This practice is under the jurisdiction of ASTM Committee F39 on Aircraft Available from National Electrical Manufacturers Association (NEMA), 1300
Systems and is the direct responsibility of Subcommittee F39.02 on Inspection, N. 17th St., Suite 900, Arlington, VA 22209, http://www.nema.org.
Alteration, Maintenance, and Repair. Available from RTCA, Inc., 1150 18th NW, Suite 910, Washington, DC 20036,
Current edition approved June 1, 2019. Published June 2019. Originally https://www.rtca.org.
approved in 2009. Last previous edition approved in 2014 as F2799–14. DOI: Available from Society of Automotive Engineers (SAE), 400 Commonwealth
10.1520/F2799–14R19. Dr., Warrendale, PA 15096, https://www.sae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2799 − 14 (2019)
ARP1870 Aerospace Systems Electrical Bonding and 3.3.17 UV—ultraviolet
Grounding for Electromagnetic Compatibility and Safety
ARP1928 TorqueRecommendationsforAttachingElectrical
4. Significance and Use
Wiring Devices to Terminal Boards or Blocks, Studs,
4.1 This practice is intended to be used as a standard wiring
Posts, etc.
practice for aircraft when not contrary to standards published
2.7 Federal Standards:
by the aircraft original equipment manufacturer (OEM) or
Advisory Circular 20-53A Protection of Aircraft Fuel Sys-
regulations. This practice is intended to be used for mainte-
tems against Fuel Vapor Ignition due to Lightning
nance and preventive maintenance of electrical wiring inter-
MIL-C-22520/2C Crimping Tools, Terminal, Hand, Wire
connection systems (EWIS).
Termination
4.2 This practice is not intended to supersede or replace any
MIL-S-8802 Sealing Compound, Temperature-Resistant, In-
government specification or specific manufacturer’s instruc-
tegral Fuel Tanks and Fuel Cell Cavities, High Adhesion
tions regarding EWIS maintenance or repair.
MIL-T-7928 Terminal, Lug Splices, Conductors, Crimp
Style, Copper
5. Maintenance
MIL-T-43435 Tape, Lacing and Tying
MS17821 Specification for Cable and Marker Color Code
5.1 Electrical Systems:
Numbers
5.1.1 Maintenance:
MS17822 Specification for Cable and Marker Color Code
5.1.1.1 Scheduled and unscheduled maintenance activities,
Numbers
if done improperly, may contribute to long-term problems and
NAVAIR 01-1A-505 Installation Practices—Aircraft Elec-
degradation of wiring. Certain repairs may have limited dura-
tric and Electronic Wiring
bility and shall be evaluated to ascertain if rework is necessary.
Repairs that conform to manufacturers’recommended mainte-
3. Terminology
nance practices are generally considered permanent and should
3.1 Definitions:
not require rework. Care shall be taken to prevent undue
3.1.1 maintenance, n—inspection, overhaul, repair,
collateral damage to EWIS while performing maintenance on
preservation, and the replacement of parts but excludes pre-
other systems. Metal shavings and debris have been discovered
ventive maintenance.
on wire bundles after maintenance, repairs, or modifications
3.2 Definitions of Terms Specific to This Standard:
have been performed. Care shall be taken to protect wire
3.2.1 electrical wiring interconnection system (EWIS),
bundles and connectors during maintenance and repair. Work
n—as used in this practice, any wire, wiring device, or
areas should be cleaned while the work progresses to ensure
combination of these, including termination devices, installed
that all shavings and debris are removed.The work area should
in any area of the aircraft for the purpose of transmitting
be thoroughly cleaned after work is complete, and the area
electrical energy between two or more intended termination
shall be inspected after the final cleaning. Maintenance,
points.
repairs, and alterations should be performed using the most
effective methods available to protect the surrounding EWIS.
3.3 Acronyms:
Since wire splices are more susceptible to degradation, arcing,
3.3.1 AC—alternating current
and overheating, the recommended method of repairing a wire
3.3.2 CFC—carbon fiber composite
is with an environmentally sealed splice. (Warning—For
3.3.3 DC—direct current
personal safety and to avoid the possibility of fire, turn off all
3.3.4 EDS—electronic data system electrical power before starting an inspection of the aircraft
electrical system or performing maintenance.)
3.3.5 EMI—electromagnetic interference
5.1.1.2 Repair of any system component that fails an elec-
3.3.6 ESD—electrostatic discharge
trical measurement test shall conform to manufacturer’s in-
3.3.7 EWIS—electrical wiring interconnection system
structions and, in lieu of manufacturer’s manuals, Practice
3.3.8 ICAO—International Civil Aviation Organization
F2639 or appropriate regulatory guidance materials.
5.1.1.3 Wire bundles should be routed in accessible areas
3.3.9 NiCad—nickel cadmium
that are protected from damage from personnel, cargo, and
3.3.10 OEM—original equipment manufacturer
maintenance activity.They should not be routed in areas where
3.3.11 PC—personal computer
they are likely to be used as handholds or as support for
3.3.12 PTFE—polytetrafluoroethylene
personal equipment or where they could become damaged
during removal of aircraft equipment.
3.3.13 RF—radio frequency
5.1.1.4 Replacement wires (see Tables 1 and 2) should be
3.3.14 SOC—state of charge
clamped so that contact with equipment and structure is
3.3.15 STC—supplemental-type certificate
avoided. Where this cannot be accomplished, extra protection
3.3.16 SWAMP—severe wind and moisture problem
in the form of grommets, chafe strips, and so forth, should be
provided. Protective grommets shall be used wherever wires
cannot be clamped in a way that ensures at least a ⁄8 in. (9.5
Available from U.S. Government Publishing Office, 732 N. Capitol St., NW,
Washington, DC 20401, http://www.gpo.gov. mm) clearance from structure at penetrations.
F2799 − 14 (2019)
TABLE 1 Open Wiring
Voltage Rating Rated Wire
Document Insulation Type Conductor Type
(Maximum) Temperature, °C
A
MIL-W-22759/1 600 200 Fluoropolymer-insulated TFE and TFE coated glass Silver-coated copper
A
MIL-W-22759/2 600 260 Fluoropolymer-insulated TFE and TFE coated glass Nickel-coated copper
A
MIL-W-22759/3 600 260 Fluoropolymer-insulated TFE-glass-TFE Nickel-coated copper
A
MIL-W-22759/4 600 200 Fluoropolymer-insulated TFE-glass-FEP Silver-coated copper
A
MIL-W-22759/5 600 200 Fluoropolymer-insulated extruded TFE Silver-coated copper
A
MIL-W-22759/6 600 260 Fluoropolymer-insulated extruded TFE Nickel-coated copper
A
MIL-W-22759/7 600 200 Fluoropolymer-insulated extruded TFE Silver-coated copper
A
MIL-W-22759/8 600 260 Fluoropolymer-insulated extruded TFE Nickel-coated copper
A
MIL-W-22759/9 1000 200 Fluoropolymer-insulated extruded TFE Silver-coated copper
A
MIL-W-22759/10 1000 260 Fluoropolymer-insulated Nickel-coated copper
A
MIL-W-22759/13 600 135 Fluoropolymer-insulated FEP PVF2 Tin-coated copper,
A
MIL-W-22759/16 600 150 Fluoropolymer-insulated extruded ETFE Tin-coated copper,
A
MIL-W-22759/17 600 150 Fluoropolymer-insulated extruded ETFE Silver-coated high-strength copper alloy
A
MIL-W-22759/20 1000 200 Fluoropolymer-insulated extruded TFE Silver-coated high-strength copper alloy
A
MIL-W-22759/21 1000 260 Fluoropolymer-insulated extruded TFE Nickel-coated high-strength copper alloy
A
MIL-W-22759/34 600 150 Fluoropolymer-insulated cross-linked modified ETFE Tin-coated copper
A
MIL-W-22759/35 600 200 Fluoropolymer-insulated cross-linked modified ETFE Silver-coated high-strength copper alloy
A
MIL-W-22759/41 600 200 Fluoropolymer-insulated cross-linked modified ETFE Nickel-coated copper
A
MIL-W-22759/42 600 200 Fluoropolymer-insulated cross-linked modified ETFE Nickel-coated high-strength copper alloy
A
MIL-W-22759/43 600 200 Fluoropolymer-insulated cross-linked modified ETFE Silver-coated copper
B B
MIL-W-25038/3/2/ 600 260 See specification sheet See specification sheet
MIL-W-81044/6 600 150 Cross-linked polyalkene Tin-coated copper
MIL-W-81044/7 600 150 Cross-linked polyalkene Silver-coated high-strength copper alloy
MIL-W-81044/9 600 150 Cross-linked polyalkene Tin-coated copper
MIL-W-81044/10 600 150 Cross-linked polyalkene Silver-coated high-strength copper alloy
MIL-W-81044/12 600 150 Cross-linked polyalkene Tin-coated copper
A
MIL-W-22759 has been replaced by SAE AS22759.
B
Inorganic fibers—glass—TFE.
TABLE 2 Protected Wiring
Voltage Rating Rated Wire
Document Insulation Type Conductor Type
(Maximum) Temperature, °C
A
MIL-W-22759/11 600 200 Fluoropolymer-insulated extruded TFE Silver-coated copper
A
MIL-W-22759/12 600 260 Fluoropolymer-insulated extruded TFE Nickel-coated copper
A
MIL-W-22759/14 600 135 Fluoropolymer-insulated FEP-PVF2 Tin-coated copper
A
MIL-W-22759/15 600 135 Fluoropolymer-insulated FEP-PVF2 Silver-plated high-strength copper alloy
A
MIL-W-22759/18 600 150 Fluoropolymer-insulated extruded ETFE Tin-coated copper
A
MIL-W-22759/19 600 150 Fluoropolymer-insulated extruded ETFE Silver-coated high-strength copper alloy
A
MIL-W-22759/22 600 200 Fluoropolymer-insulated extruded TFE Silver-coated high-strength copper alloy
A
MIL-W-22759/23 600 260 Fluoropolymer-insulated extruded TFE Nickel-coated high-strength copper alloy
A
MIL-W-22759/32 600 150 Fluoropolymer-insulated cross-linked modified ETFE Tin-coated copper
A
MIL-W-22759/33 600 200 Fluoropolymer-insulated cross-linked modified ETFE Silver-coated high-strength copper alloy
A
MIL-W-22759/44 600 200 Fluoropolymer-insulated cross-linked modified ETFE Silver-coated copper
A
MIL-W-22759/45 600 200 Fluoropolymer-insulated cross-linked modified ETFE Nickel-coated copper
A
MIL-W-22759/46 600 200 Fluoropolymer-insulated cross-linked modified ETFE Nickel-coated high-strength copper alloy
MIL-W-81044/13 600 150 Cross-linked polyalkene – PVF2 Silver-coated high-strength copper alloy
MIL-W-81381/17 600 200 Fluorocarbon polyamide Silver-coated copper
MIL-W-81381/18 600 200 Fluorocarbon polyamide Nickel-coated copper
MIL-W-81381/19 600 200 Fluorocarbon polyamide Silver-coated high-strength copper alloy
MIL-W-81381/20 600 200 Fluorocarbon polyamide Nickel-coated high-strength copper alloy
MIL-W-81381/21 600 150 Fluorocarbon polyamide Tin-coated copper
A
MIL-W-22759 has been replaced by SAE AS22759.
5.1.1.5 Wire should not have a preload against the corners 5.1.2.1 The term “electrical wiring interconnection system
or edges of chafing strips or grommets. Wiring shall be routed (EWIS)” as used in this practice means any wire, wiring
away from high-temperature equipment and lines to prevent device, or combination of these, including termination devices,
deterioration of insulation. Protective flexible conduits should installed in any area of the aircraft for the purpose of
be made of a material and design that eliminates the potential transmitting electrical energy between two or more intended
of chafing between their internal wiring and the conduit termination points.
internal walls. 5.1.2.2 The satisfactory performance of an aircraft is depen-
5.1.1.6 Replacement wires that shall be routed across dent upon the continued reliability of the electrical system.
hinged panels should be routed and clamped so that the bundle Damaged wiring or equipment in an aircraft, regardless of how
will twist, rather than bend, when the panel is moved. minor it may appear to be, cannot be tolerated. Reliability of
5.1.2 General: the system is proportional to the amount of maintenance
F2799 − 14 (2019)
received and the knowledge of those who perform such and are easily damaged by rough handling, abuse, overheating,
maintenance. It is, therefore, important that maintenance be or reversing the battery connections.The battery shall never be
accomplished using the best techniques and practices to connected with reversed polarity as this may subject the diodes
minimize the possibility of failure. to a forward bias condition allowing very high-current conduc-
tion that will generally destroy them instantly.
5.1.3 Cleaning and Preservation:
5.2.2 Acceptable Means of Controlling or Monitoring the
5.1.3.1 Annual cleaning of electrical equipment to remove
Electrical Load—For detailed guidance for analyzing electrical
dust, dirt, and grime is recommended.
loads, refer to Guide F2490.
5.1.3.2 If terminals and mating surfaces are corroded or
dirty, suitable solvents or fine abrasives that will not score the
5.3 Circuit Protection Devices:
surface or remove the plating may be used to clean them. Only
5.3.1 Circuit Breaker Maintenance:
cleaning agents that do not leave any type of residue shall be
5.3.1.1 Resettable circuit breakers should be cycled with no
used. Avoid using emery cloth to polish commutators or slip
load to enhance contact performance by cleaning contaminants
rings because particles may cause shorting and burning. Be
from the contact surfaces. Unless specified in the aircraft or
sure that protective finishes are not scored or damaged when
component maintenance instructions, it is recommended that
cleaning. Ensure that metal-to-metal electrically bonded sur-
each resettable circuit breaker be pulled and reset as part of the
faces are treated at the interface with a suitable anticorrosive
aircraft annual inspection.
conductive coating and that the joint is sealed around the edges
5.3.1.2 Breakers with broken or missing parts shall be
by restoring the original primer and paint finish. Connections
replaced.
that shall withstand a highly corrosive environment may be
5.3.1.3 Before considering replacement of circuit breakers
encapsulated with an approved sealant to prevent corrosion.
that have a tendency to open circuits frequently, require
(Warning—Turn power off before cleaning.)
resetting more than normal, or are subject to nuisance tripping,
5.1.3.3 “Protect and Clean As You Go” Philosophy—It is
investigate and correct the reason.
imperative that the technician performing maintenance and
5.3.2 Relays—A relay is an electrically controlled device
repairs to the aircraft takes protective measures when working
that opens and closes electrical contacts to effect the operation
on or around wire bundles and connectors to protect the EWIS
of other devices in the same or in another electrical circuit.The
from damage. It is important to protect EWIS during airframe
relay converts electrical energy into mechanical energy
repairs, alterations, or other aircraft maintenance by ensuring
through various means and, through mechanical linkages,
that metal shavings, debris, and contamination resulting from
actuates electrical conductors (contacts) that control electrical
such work are removed.
circuits. Solid- state relays may also be used in electrical
5.1.4 Battery Electrolyte Corrosion—Corrosion found on or
switching applications.
near lead-acid batteries can be removed mechanically with a
5.3.2.1 Relay Installation and Maintenance—For installa-
stiff bristle brush and then chemically neutralized. For lead-
tion and maintenance, care should be taken to ensure proper
acid batteries, a 10 % sodium bicarbonate and water solution
placement of hardware, especially at electrical connections.
can be used to neutralize the electrolyte. For nickel cadmium
The use of properly calibrated torque wrenches and following
(NiCad) batteries, a 3 % solution of acetic acid can be used to
the manufacturer’s installation procedures is strongly recom-
neutralize the electrolyte.After neutralizing, the battery should
mended. This is especially important with hermetically sealed
be washed with clean water and thoroughly dried.
relays, since the glass-to-metal seal (used for insulation of the
5.1.5 Adjustment and Repair:
electrically “live” components) is especially vulnerable to
5.1.5.1 Accomplish adjustments to items of equipment such
catastrophic failure as a result of overtorquing.
as regulators, alternators, generators, contactors, control
(1) WhenreplacingrelaysinACapplications,itisessential
devices, inverters, and relays at a location outside the aircraft
to maintain proper phase sequencing. For any application
and on a test stand or test bench where all necessary instru-
involving plug-in relays, proper engagement of their retaining
ments and test equipment are at hand. Follow the adjustment
mechanism is vital.
and repair procedures outlined by the equipment or aircraft
(2) The proximity of certain magnetically permanent,
manufacturer. Replacement or repair shall be accomplished as
magnet-assisted, coil-operated relays may cause them to have
a part of routine maintenance.
animpactoneachother.Anymanufacturer’srecommendations
5.1.5.2 Adjustment of a replacement voltage regulator is
or precautions shall be followed.
likely since there will always be a difference in impedance
5.3.2.2 Switches—When a switch is activated, it should
between the manufacturer’s test equipment and the aircraft’s
have a noticeable detent feel when switched. If a switch does
electrical system.
not have a detent feel when switching, it is suspect and further
5.1.6 Bus Bars—Bus bars that exhibit corrosion, even in inspection shall be done before considering it airworthy. Any
limited amounts, should be disassembled, cleaned, and rein-
switch with a soft or spongy feel when switched shall be
stalled Grease, corrosion, or dirt on any electrical junction may
replaced.
cause the connections to overheat and eventually fail.
6. Storage Batteries
5.2 Equipment Installation:
5.2.1 Alternator Diodes—Alternators use diodes for the 6.1 BatteryCharging—Chargingofstoragebatteriesbeyond
purpose of converting the alternating current (AC to direct their charging voltage limits can result in excessive cell
current (DC)). These diodes are solid-state electronic devices temperatures leading to electrolyte boiling, rapid deterioration
F2799 − 14 (2019)
of the cells, and battery failure. The relationship between eralized water. Because the fluid level varies with the state of
maximum charging voltage and the number of cells in the charge, water should never be added while the battery is
battery is also significant. This will determine (for a given installed in the aircraft. Overfilling the battery will result in
ambient temperature and state of charge) the rate at which electrolyte spewage during charging. This will cause corrosive
energy is absorbed as heat within the battery. For lead-acid effects on the cell links, self-discharge of the battery, dilution
batteries, the voltage per cell shall not exceed 2.35 V. In the of the electrolyte density, possible blockage of the cell vents,
case of NiCad batteries, the charging voltage limit varies with and eventual cell rupture.
design and construction. Values of 1.4 and 1.5 V per cell are 6.1.1.8 Lead-acid batteries are usually charged by regulated
generally used. In all cases, follow the recommendations of the DC voltage sources. This allows maximum accumulation of
battery manufacturer. charge in the early part of recharging.
6.1.1.9 Constant-current battery chargers are usually pro-
6.1.1 Battery and Charger Characteristics—The following
vided for NiCad batteries because the NiCad cell voltage has a
information is provided to acquaint the user with characteris-
negative temperature coefficient. With a constant-voltage
tics of the more common aircraft battery and battery charger
charging source, a NiCad battery having a shorted cell might
types. Products may vary from these descriptions because of
overheat because of excessive overcharge and undergo a
different applications of available technology. Consult the
thermal runaway, destroying the battery and creating a possible
manufacturer for specific performance data. (Warning—
safety hazard to the aircraft.
Under no circumstances connect a lead-acid battery to a
(1) Definition—Thermal runaway can result in a chemical
charger unless the battery is properly serviced. )
fire or explosion or both of the NiCad battery under recharge
6.1.1.1 Lead-acid vented batteries have a 2 V nominal cell
by a constant-voltage source and is due to cyclical, ever-
voltage. Batteries are constructed so that individual cells
increasing temperature and charging current. One or more
cannot be removed. Occasional addition of water is required to
shorted cells or an existing high temperature and low charge
replace water loss caused by overcharging in normal service.
can produce the cyclical sequence of events:
Batteries that become fully discharged may not accept re-
(a) Excessive current,
charge.
(b) Increased temperature,
6.1.1.2 Lead-acid sealed batteries are similar in most re-
(c) Decreased cell(s) resistance,
spects to lead-acid vented batteries but do not require the
(d) Further increased current, and
addition of water.
(e) Further increased temperature. This will not become a
6.1.1.3 The lead-acid battery is economical and has exten-
self-sustaining thermal-chemical action if the constant-voltage
sive application but is heavier than an equivalent performance
charging source is removed before the battery temperature is in
battery of another type. The battery is capable of a high rate of
excess of 160 °F (71.1 °C).
discharge and low-temperature performance. However, main-
6.1.1.10 Pulsed-current battery chargers are sometimes pro-
taining a high rate of discharge for a period of time usually
vided for NiCad batteries. (Warning—It is important to use
warpsthecellplates,shortingoutthebattery.Itselectrolytehas
the proper charging procedures for batteries under test and
a moderate specific gravity, and state of charge can be checked
maintenance. These charging regimes for reconditioning and
with a hydrometer.
charging cycles are defined by the aircraft manufacturer and
6.1.1.4 Do not use high-amperage automotive battery char-
should be closely followed.)
gers to charge aircraft batteries.
6.2 Battery Freezing—Discharged lead-acid batteries ex-
6.1.1.5 NiCad vented batteries have a 1.2-V nominal cell
posed to cold temperatures are subject to plate damage because
voltage. Occasional addition of distilled water is required to
of freezing of the electrolyte. To prevent freezing damage,
replace water loss caused by overcharging in normal service.
maintaineachcell’sspecificgravityatnolessthan1.275or,for
Cause of failure is usually shorting or weakening of a cell.
sealed lead-acid batteries, check “open” circuit voltage (see
After replacing the bad cell with a good cell, the battery’s life
Table 3). The NiCad battery electrolyte is not as susceptible to
can be extended for five or more years. Full discharge is not
freezing because no appreciable chemical change takes place
harmful to this type of battery.
6.1.1.6 NiCadsealedbatteriesaresimilarinmostrespectsto
NiCadventedbatteriesbutdonotnormallyrequiretheaddition
TABLE 3 Lead-Acid Battery Electrolyte Freezing Points
of water. Fully discharging the battery (to 0 V) may cause
State of Charge (SOC)
irreversible damage to one or more cells leading to eventual
Freeze Point for Sealed Lead-Acid Batteries
Specific
battery failure as a result of low capacity.
at 21.1 °C (70 °F)
Gravity
6.1.1.7 The state of charge of a NiCad battery cannot be
°C °F SOC 12 V 24 V
determined by measuring the specific gravity of the potassium
1.300 -70 -95 100% 12.9 25.8
hydroxide electrolyte. The electrolyte specific gravity does not 1.275 -62 -80 75% 12.7 25.4
1.250 -52 -62 50% 12.4 24.8
change with the state of charge. The only accurate way to
1.225 -37 -35 25% 12.0 24.0
determine the state of charge of a NiCad battery is by a
1.200 -26 -16
measured discharge with a NiCad battery charger and follow- 1.175 -20 -4
1.150 -15 +5
ing the manufacturer’s instructions. After the battery has been
1.125 -10 +13
fully charged and allowed to stand for at least 2 h, the fluid
1.100 -8 +19
level may be adjusted, if necessary, using distilled or demin-
F2799 − 14 (2019)
TABLE 4 Sulfuric Acid Temperature Correction
tenance manual’s installation procedures. Always follow pro-
Points to be cedures approved for the specific aircraft and battery system to
Electrolyte Temperature
Subtracted or Added to
ensure that the battery system is capable of delivering specified
°C °F
Specific Gravity Readings
performance.
60 140 +24
55 130 +20
6.5 NoxiousFumes—Whenchargingratesareexcessive,the
49 120 +16
electrolyte may boil to the extent that fumes containing
43 110 +12
droplets of the electrolyte are emitted through the cell vents.
38 100 +8
33 90 +4
These fumes from lead-acid batteries may become noxious to
27 80 0
the crew members and passengers; therefore, thoroughly check
23 70 -4
the venting system. NiCad batteries will emit gas near the end
15 60 -8
10 50 -12
of the charging process and during overcharge. The battery
540 -16
vent system in the aircraft should have sufficient air flow to
-2 30 -20
prevent this explosive mixture from accumulating. It is often
-7 20 -24
-13 10 -28
advantageous to install a jar in the battery vent discharge
-18 0 -32
system serviced with an agent to neutralize the corrosive effect
-23 -10 -36
of battery vapors.
-28 -20 -40
-35 -30 -44
6.6 Installation Practices:
6.6.1 External Surface—Clean the external surface of the
battery before installation in the aircraft.
6.6.2 Battery Venting—Battery fumes and gases may cause
between the charged and discharged states. However, the
an explosive mixture or contaminated compartments and
electrolyte will freeze at approximately minus –75 °F
should be dispersed by adequate ventilation. The technician
(59.4 °C).
NOTE 2—Only a load check will determine overall battery condition. should ensure that the battery venting system is reinstalled and
verified following battery installation.
6.3 Temperature Correction—U.S. manufactured lead-acid
6.6.3 Battery Sump Jars—A battery sump jar installation
batteries are considered fully charged when the specific gravity
maybeincorporatedintheventingsystemtodisposeofbattery
reading is between 1.275 and 1.300. A ⁄3 discharged battery
2 electrolyte overflow. The technician should ensure that the
reads about 1.240 and a ⁄3 discharged battery will show a
battery sump jar is serviced following installation of a battery.
specific gravity reading of about 1.200 when tested by a
6.6.4 Installing Batteries—When installing batteries in an
hydrometer and the electrolyte temperature is 26.7 °C (80 °F).
aircraft, exercise care to prevent inadvertent shorting of the
However, to determine precise specific gravity readings, a
battery terminals. Serious damage to the aircraft structure
temperature correction (see Table 4) should be applied to the
(frame, skin and other subsystems, avionics, wire, fuel, and so
hydrometer indication. As an example, with a hydrometer
forth) can be sustained by the resultant high discharge of
reading of 1.260 and the temperature of the electrolyte at 40 °F
electrical energy. This condition may normally be avoided by
(4.4 °C), the corrected specific gravity reading of the electro-
insulating the terminal posts during the installation process.
lyte is 1.244.
During battery removal, remove the grounding lead first, then
6.4 Battery Maintenance—Battery inspection and mainte-
the positive lead. For installation of a battery, connect the
nance procedures vary with the type of chemical technology
grounding lead of the battery last to minimize the risk of
and physical construction.Always follow the battery manufac-
shorting the “hot terminal” of the battery.
turer’s approved procedures.
6.6.5 Battery Hold-Down Devices—Ensure that the battery
hold-down devices are secure but not so tight as to exert
NOTE 3—Careful examination of sealed batteries and proper recondi-
tioning of vented batteries will ensure the longest possible service life.
excessive pressure that may cause the battery to buckle
resulting in internal shorting of the battery.
6.4.1 Use a hydrometer to determine the specific gravity of
6.6.6 Quick-Disconnect-Type Battery—If a quick-
the battery electrolyte, which is the weight of the electrolyte
disconnect-type of battery connector that prohibits crossing the
compared to the weight of pure water.
battery lead is not used, ensure that the aircraft wiring is
6.4.2 Take care to ensure the electrolyte is returned to the
connectedtotheproperbatteryterminal.Reversepolarityinan
cell from which it was extracted. When a specific gravity
electrical system can seriously damage a battery and other
difference of 0.050 or more exists between cells of a battery,
electrical components. Ensure that the battery cable connec-
the battery is approaching the end of its useful life and
tions are tight to prevent arcing or a high-resistance connec-
replacement should be considered. Electrolyte level may be
tion.
adjusted by the addition of distilled water.
6.4.3 Mechanical Integrity—Proper mechanical integrity in-
7. Aircraft Electrical Wire Selection
volves the absence of any physical damage as well as an
assurance that the hardware is correctly installed and the 7.1 The following are considered principal causes of wiring
battery is properly connected. A battery and battery compart- degradation and should be used to help focus maintenance
ment venting system prevent the buildup of explosive gases programs:
and should be checked periodically to ensure that they are 7.1.1 Vibration—High-vibration areas tend to accelerate
securely connected and oriented in accordance with the main- degradation over time resulting in “chattering” contacts and
F2799 − 14 (2019)
intermittent symptoms. High vibration of tie-wraps or string 7.2.4 Theuseofcurrentmilitaryspecification,multiconduc-
ties can cause damage to insulation. In addition, high vibration tor cables in place of OEM-installed constructions may create
will worsen any existing wire insulation cracking. problems such as color sequence. Some civilian aircraft are
7.1.2 Moisture—High-moisture areas generally accelerate wiredwiththeoldercolorsequenceusing“red-blue-yellow”as
corrosion of terminals, pins, sockets, and conductors. Note that the first three colors. Current military specification, multicon-
wiring installed in clean, dry areas with moderate temperatures ductor cables, in accordance with MIL-C-27500, use “white-
appears to hold up well. blue-orange” for the initial three colors. During the repair of
7.1.3 Maintenance—Scheduled and unscheduled mainte- EWIS,thetechniciansshouldfollowwhichevercolorsequence
nance activities, if done improperly, may contribute to long- that is currently used in the aircraft. Deviating from the
term problems and degradation of wiring. existing color sequence is considered an alteration and Practice
7.1.4 Repairs—Certain repairs may have limited durability F2639 should be consulted.
and shall be evaluated to ascertain if rework is necessary.
Repairs that conform to manufacturers’recommended mainte- 8. Wiring Installation Requirements
nance practices are generally considered permanent and should
8.1 General—Repairs to wires and cables should be in-
not require rework. Repairs should be performed using the
stalled with adequacy of support and protection. Accordingly,
most effective methods available. Since wire splices are more
aircraft wiring shall be maintained to the following require-
susceptible to degradation, arcing, and overheating, the recom-
ments:
mended method of repairing a wire is with an environmentally
8.1.1 Wires and cables should be supported by suitable
sealed splice.
clamps, grommets, or other devices at intervals of not more
7.1.5 Clean as You Go—Care shall be taken to prevent
than 24 in. (61 cm), except when contained in troughs, ducts,
undue collateral damage to EWIS while performing mainte-
orconduits.Thesupportingdevicesshouldbeofasuitablesize
nance on other systems. Metal shavings and debris have been
and type with the wires and cables held securely in place
discovered on wire bundles after maintenance, repairs, or
withoutdamagetotheinsulation.“Fill”materialsshouldnotbe
modifications have been performed. Care shall be taken to
used in lieu of a suitable sized clamp.
protect wire bundles and connectors during modification work.
8.1.2 Standoffs should be used to maintain clearance be-
Work areas should be cleaned while the work progresses to
tween wires and structure. Using tape or tubing is not accept-
ensure that all shavings and debris are removed.The work area
able as an alternative to standoffs for maintaining clearance.
should be thoroughly cleaned after work is complete, and the
8.1.3 Phenolic blocks, plastic liners, or rubber grommets
area shall be inspected after the final cleaning.
should be installed in holes, bulkheads, floors, or structural
7.2 Substitutions: members where it is impossible to install off-angle clamps to
7.2.1 In the repair and modification of existing aircraft, maintainwiringseparation.Insuchcases,additionalprotection
when a replacement wire is required, the maintenance manual in the form of plastic or insulating tape may be used.
for that aircraft shall first be reviewed to determine if the 8.1.4 Wires and cables in junction boxes, panels, and
original aircraft manufacturer has approved any substitution. bundles should be properly supported and laced to provide
7.2.2 If the original aircraft manufacturer has not approved proper grouping and routing.
a substitute wire, the technician should use standard wire as 8.1.5 Clamp-retaining screws should be properly secured so
specified in Table 1, Table 2 and Table 5 (reference Practice that the movement of wires and cables is restricted to the span
F2639) or other applicable regulatory guidance. between the points of support and not on soldered or mechani-
7.2.3 Areas designated as severe wind and moisture prob- cal connections at terminal posts or connectors.
lem (SWAMP) areas differ from aircraft to aircraft but gener- 8.1.6 Wire and cables should be properly supported and
ally are considered to be areas such as wheel wells, near wing bound so that there is no interference with other wires, cables,
flaps, wing folds, pylons, and other exterior areas that may and equipment.
have a harsh environment. Wires for these applications often 8.1.7 Wires and cables should be adequately supported to
have design features incorporated into their construction that prevent excessive movement in areas of high vibration.
may make the wire unique; therefore, an acceptable substitu- 8.1.8 Insulating tubing should be secured by tying, tie
tion may be difficult, if not impossible, to find. It is very straps, or with clamps.
important to use the wire type recommended in the aircraft 8.1.9 Continuous lacing (spaced 6 in. (15 cm) apart) should
manufacturer’s maintenance handbook. not be used except in panels and junction boxes.
TABLE 5 Coaxial Cable Selection
Impedance Rated Cable Outer Diameter, Jacket Type/
Document Part Number
(Ω) Temperature (°C) Nominal (in.) Dielectric Type
MIL-C-17/060 M17/060-RG142 50 200 0.195 FEP/PTFE
MIL-C-17/93 M17/93-RG178 50 200 0.071 FEP/PTFE
MIL-C-17/94 M17/94-RG179 75 200 0.100 FEP/PTFE
MIL-C-17/113 M17/113-RG316 50 200 0.098 FEP/PTFE
MIL-C-17/127 M17/127-RG393 50 200 0.390 FEP/PTFE
MIL-C-17/128 M17/128-RG400 50 200 0.195 FEP/PTFE
F2799 − 14 (2019)
8.1.10 Do not use tapes (such as friction or plastic tape) that possible from the lowest point or otherwise provide with a
willdryoutinservice,producechemicalreactionswithwireor moisture-proof covering.
cable insulation, or absorb moisture.
8.1.20 Separate wires from high-temperature equipment
8.1.11 Insulating tubing should be kept at a minimum and such as resistors, exhaust stacks, heating ducts, and so forth to
shall be used to protect wire and cable from abrasion, chafing,
prevent insulation breakdown. Insulate wires that must run
exposure to fluid, and other conditions that could affect the through hot areas with a high-temperature insulation material
cableinsulation.However,insulatingtubingshouldnotbeused
such as fiberglass or polytetrafluoroethylene (PTFE).
to support wires and cable in lieu of standoffs.
NOTE 4—The minimum radius of bends in wire groups or bundles shall
8.1.12 Do not tie or fasten wires and cables together in
not be less than ten times the outside diameter of the largest wire or cable,
conduit or insulating tubing.
except that at the terminal strips where wires break out at terminations or
8.1.13 Ensure cable supports do not restrict the wires or
reverse direction in a bundle. Where the wire is suitably supported, the
radiusmaybethreetimesthediameterofthewireorcable.Whereitisnot
cables in such a manner as to interfere with operation of
practical to install wiring or cables within the radius requirements, the
equipment shock mounts.
bend should be enclosed in insulating tubing.The radius for thermocouple
8.1.14 Do not use tape or cord for primary support.
wire should be determined in accordance with the manufacturer’s recom-
8.1.14.1 Only aviation-grade tie straps should be used on
mendation and shall be sufficient to avoid excess losses or damage to the
aircraft and should only be used for their intended function. cable. The bend radius of RF cables, for example, coaxial and triaxial,
should be no less than six times the outside diameter of the cable.
8.1.15 Make sure that drain holes are present in drip loops
or in the lowest portion of tubing placed over the wiring. See
8.1.21 Ensure that replacement wires and cables that are
Fig. 1.
attached to assemblies where relative movement occurs (such
8.1.16 Ensure that wires and cables are routed in such a
as at hinges and rotating pieces, particularly doors, control
manner that chafing will not occur against the airframe or other
sticks, control wheels, columns, and flight control surfaces) are
components.
installed or protected in such a manner as to prevent deterio-
8.1.17 Ensure that replacement wires and cables in wheel
ration of the wires and cables caused by the relative movement
wells and other areas where they may be exposed to damage
of the assembled parts.
from impact of rocks, ice, mud, and so forth are adequately
8.1.22 Ensure that replacement wires and electrical cables
protected.
are separated from mechanical control cables. In no instance
8.1.17.1 Replacementwirecloserthan2in.(5cm)fromany 1
should wire be able to come closer than ⁄2 in. (1.3 cm) to such
flammable liquid, fuel, oxygen line, or fuel tank wall should be
controls when light hand pressure is applied to wires or
closelyclampedandrigidlysupportedandtiedatintervalssuch
controls. In cases in which clearance is less than this, adequate
that contact between such lines, related equipment, fuel tank
support shall be provided to prevent chafing.
walls, or other wires will not occur, assuming a broken wire
8.1.23 Ensure that replacement wires and cables are pro-
and a missing wire tie or clamp.
vided with enough slack (see Fig. 2) to meet the following
8.1.18 Ensure that a trap or drip loop is provided to prevent
requirements:
fluids or condensed moisture from running into wires and
8.1.23.1 Permit ease of maintenance;
cablesdresseddownwardtoaconnector,terminalblock,panel,
8.1.23.2 Prevent mechanical strain on the wires, cables,
or junction box.
junctions, and supports;
8.1.19 Route replacement wires and cables installed in
8.1.23.3 Permit free movement of shock and vibration
bilgesandotherlocationswherefluidsmaybetrappedasfaras
mounted equipment; and
8.1.23.4 Allow shifting of equipment, as necessary, to
perform alignment, servicing, tuning, removal of dust covers,
andchangingofinternalcomponentswhileinstalledinaircraft.
8.1.24 Ensure that unused wires are individually dead
ended, tied into a bundle, and secured to a permanent structure.
Each wire should have strands cut even with the insulation and
a pre-insulated closed end connector or a 1 in. (2.5 cm) piece
of insulating tubing placed over the wire with its end folded
back and tied.
8.1.25 Ensure that all replacement wires and cables are
identified properly (if the data are available in the aircraft
maintenance manuals) at intervals of not more than 15 in. (38
cm). Coaxial cables are identified at both equipment ends.
8.1.25.1 Replace corroded connections and overheated con-
nectors.
8.1.25.2 Wire bundles may consist of two or more groups of
wires. Replacement wires should be placed within the wiring
bundle or group to which the original wire was attached.
Replacement wires shall not be attached to the outside of the
FIG. 1 Dr
...