1、Designation: F 2696 08Standard Practice forInspection of Airplane Electrical Wiring Systems1This standard is issued under the fixed designation F 2696; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A nu
2、mber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers basic inspection procedures forelectrical wiring interconnect systems for normal and utilitycategory aircraft elect
3、rical wiring systems.1.2 This practice is not intended to replace any instructionsfor continued airworthiness published by the aircraft or acces-sory manufacturer or type design holder.1.3 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathem
4、aticalconversions to SI units that are provided for information onlyand are not considered standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and heal
5、th practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 Military Standard:2MIL-C-85049 Connector Accessories, Electrical, GeneralSpecification for2.2 FAA Guidance Material:3FAA Advisory Circular 33.4-3 Instructions for ContinuedAirworthiness; A
6、ircraft Engine High Intensity RadiatedFields (HIRF) and Lightning Protection Features2.3 SAE Documents:4SAE ARP1870 Aerospace Systems Electrical Bonding andGrounding for Electromagnetic Compatibility and SafetySAE Aerospace ARP5583 Guide to Certification of Aircraftin a High Intensity Radiated Field
7、 (Hirf) Environment3. Terminology3.1 Acronyms:3.1.1 EWISelectrical wiring interconnection system3.1.2 HIRFhigh-intensity radiated fields3.1.3 ICAinstructions for continued airworthiness3.1.4 LRUline-replaceable unit3.1.5 MSmilitary standard3.1.6 MTBFmean time between failures3.1.7 PTFEpolytetrafluor
8、oethylene3.1.8 RFradio frequency3.1.9 STCsupplemental type certificate (Federal AviationAdministration)4. Significance and Use4.1 The term “electrical system” as used in this practicemeans those parts of the aircraft that generate, distribute, anduse electrical energy, including their support and at
9、tachments.4.2 The satisfactory performance of an aircraft is dependentupon the continued reliability of the electrical system.4.3 Damaged wiring or equipment in an aircraft, regardlessof how minor it may appear to be, cannot be tolerated. It is,therefore, important that maintenance be accomplished u
10、singthe best techniques and practices to minimize the possibility offailure.4.4 When inspecting and evaluating EWIS, improper wir-ing, routing, or repairs shall be corrected regardless of theorigin of the error.4.5 This practice is not intended to supersede or replace anygovernment specification or
11、specific manufacturers instructionregarding electrical system inspection and repair5. Causes of Wire Degradation5.1 The following are considered the principal causes ofwiring degradation and should be used to help focus mainte-nance programs:5.1.1 VibrationHigh-vibration areas tend to acceleratedegr
12、adation over time resulting in “chattering” contacts andintermittent symptoms. High vibration of tie-wraps or stringties can cause damage to insulation. In addition, high vibrationwill exacerbate any existing wire insulation cracking.5.1.2 MoistureHigh-moisture areas generally acceleratecorrosion of
13、 terminals, pins, sockets, and conductors. Note thatwiring installed in clean, dry areas with moderate temperaturesappears to hold up well.5.1.3 MaintenanceScheduled and unscheduled mainte-nance activities, if done improperly, may contribute to long-term problems and degradation of wiring. Metal sha
14、vings anddebris have been discovered on wire bundles after mainte-nance, repair, or alteration work has been performed. Extra1This practice is under the jurisdiction of ASTM Committee F39 on Normal andUtility Category Airplane Electrical Wiring Systems and is the direct responsibilityof Subcommittee
15、 F39.02 on Inspection, Maintenance, and Repair.Current edition approved Jan. 15, 2008. Published February 2008.2Available from the U.S. Government Printing Office, Superintendent ofDocuments, Stop: SSOP, Washington, DC 20402-0001.3Available from Federal Aviation Administration (FAA), 800 Independenc
16、eAve., SW, Washington, DC 20591, http:/www.faa.gov.4Available from Society of Automotive Engineers (SAE), 400 CommonwealthDr., Warrendale, PA 15096-0001, http:/www.sae.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.attention sha
17、ll be given to EWIS inspections around areas ofprevious aircraft maintenance, repair, or alterations.5.1.4 RepairSince wire splices are more susceptible todegradation, arcing, and overheating, extra care shall be givenwhen inspecting repaired wiring.5.1.5 AlterationsAlterations introduce another are
18、a forenhanced scrutiny for similar reasons as repairs. In addition, analteration may not be documented in the aircraft Instructionsfor Continued Airworthiness and therefore need independentinspection and a concern for proper wiring, attachments,mounting, and wiring routing.5.1.6 Indirect DamageEvent
19、s such as pneumatic ductruptures or duct clamp leakage can cause damage that, whilenot initially evident, can later cause wiring problems. Whenevents such as these occur, surrounding EWIS shall be care-fully inspected to ensure that there is no damage or potentialfor damage evident. Indirect damage
20、caused by these types ofevents may be broken clamps or ties, broken wire insulation, oreven broken conductor strands. In some cases, the pressure ofthe duct rupture may cause wire separation from the connectoror terminal strip.6. Procedure6.1 Inspection and Operation ChecksInspect equipment,electric
21、al assemblies, and wiring installations for damage,general condition, and proper functioning to ensure the con-tinued satisfactory operation of the electrical system. Adjust,repair, overhaul, and test electrical equipment and systems inaccordance with the recommendations and procedures in theaircraf
22、t or component manufacturers maintenance instructionsor both. Replace components of the electrical system that aredamaged or defective with identical parts, aircraft manufactur-ers approved equipment, or its equivalent to the original inoperating characteristics, mechanical strength, and environ-men
23、tal specifications. A list of suggested problems to look forand checks to be performed are:6.1.1 Damaged, discolored, or overheated equipment, con-nections, wiring, and installations;6.1.2 Excessive heat or discoloration at high-current-carrying connections;6.1.3 Misalignment of electrically driven
24、equipment;6.1.4 Poor electrical bonding (broken, disconnected, orcorroded bonding strap) and grounding, including evidence ofcorrosion;6.1.5 Dirty equipment and connections;6.1.6 Improper, broken, inadequately supported wiring andconduit, loose connections of terminals, and loose ferrules;6.1.7 Poor
25、 mechanical or cold solder joints;6.1.8 Condition of circuit breaker and fuses;6.1.9 Insufficient clearance between exposed current-carrying parts and ground or poor insulation of exposedterminals;6.1.10 Broken or missing safety wire, broken bundle lacing,cotter pins, and so forth;6.1.11 Operational
26、 check of electrically operated equipmentsuch as motors, inverters, generators, batteries, lights, protec-tive devices, and so forth;6.1.12 Condition of electric lamps; and6.1.13 Missing safety shields on exposed high-voltage ter-minals (that is, 115/200 V ac).6.2 Functional Check of Standby or Emer
27、gencyEquipmentAn aircraft should have functional tests per-formed at regular intervals as prescribed by the manufacturer.6.3 Bus BarsAnnually check bus bars for general condi-tion, cleanliness, and security of all attachments and terminals.Grease, corrosion, or dirt on any electrical junction may ca
28、usethe connections to overheat and eventually fail. Bus bars thatexhibit corrosion, even in limited amounts, shall be disas-sembled, cleaned and brightened, and reinstalled.6.4 Generating SystemInspect generator(s)/alternator(s)for general condition, cleanliness, and security of attachmentand termin
29、als. Any sign of overheating terminals or wiring isreason for rejection. Inspect drive belts for condition and wear.Replace any belt showing signs of abnormal wear or overheat-ing. Inspect brushes for proper condition and wear patterns.Inspect brush holders for condition and signs of arcing oroverhe
30、ating. Inspect voltage regulation components and wiringfor condition and security. Inspect generator(s)/alternator(s)warning system for condition and operation.6.5 Battery InspectionBattery inspection procedures varywith the types of chemical technology and physical construc-tion. Always follow the
31、battery manufacturers approved pro-cedures. Battery performance at any time in a given applicationwill depend upon the batterys age, state of health, state ofcharge, and mechanical integrity.6.5.1 Aircraft Battery Inspection:6.5.1.1 Inspect battery sump jar (if installed) and lines forcondition and
32、security.6.5.1.2 Inspect battery terminals and quick-disconnect plugsand pins for evidence of corrosion, pitting, arcing, and burns.Clean as required. Inspect battery cables for condition andsigns of chafing.6.5.1.3 Inspect battery drain and vent lines for restriction,deterioration, and security. Ba
33、ttery drain areas shall be checkedfor signs of structure corrosion.6.5.1.4 Routine preflight and postflight inspection proce-dures shall include observation for evidence of physicaldamage, loose connections, and electrolyte loss.6.5.1.5 Perform capacity performance test of battery permanufacturers i
34、nstructions to ensure continued airworthiness.6.5.1.6 Inspect battery warning system components (if in-stalled) for condition and operation.6.5.1.7 For nickel-cadmium battery installations, inspectbattery temperature sensing, over-temperature warning, andbattery failure-sensing systems for proper op
35、eration. Inspectthe means for disconnecting the battery(ies) for the chargingsource in the event of an over-temperature condition.6.6 Emergency Power Supply/Battery Inspection:6.6.1 Emergency power supplies or batteries shall be in-spected and functionally tested per the manufacturer instruc-tions.6
36、.6.2 Perform capacity performance tests of batteries permanufacturers instructions to ensure continued airworthiness.6.6.3 Inspect installations for condition, security, and rout-ing of wiring.6.7 Electrical Switch Inspection:F26960826.7.1 Special attention should be given to electrical circuitswitc
37、hes, especially the spring-loaded type, during the courseof normal airworthiness inspection. An internal failure of thespring-loaded type may allow the switch to remain closed eventhough the toggle or button returns to the OFF position. Duringinspection, attention should also be given to the possibi
38、lity thatan unapproved switch substitution may have been made.6.7.1.1 With the power off, suspect aircraft electricalswitches should be checked in the ON position for opens (highresistance) and in the OFF position for shorts (low resistance)with an ohmmeter.Apower-on check can be made by checkingthe
39、 voltage drop across the switch. A voltage drop across theswitch indicates abnormal internal resistance of the switchcontacts.6.7.1.2 Any abnormal side-to-side movement of the switchshould be an alert to imminent failure even if the switch testedwas shown to be acceptable with an ohmmeter.6.7.1.3 Wh
40、en a switch is activated, it should have a notice-able detent feel when switched. If a switch does not have adetent feel when switching, it is suspect and further inspectionshall be done before considering it airworthy. Any switch witha soft or spongy feel when switched shall be replaced.6.7.1.4 Eac
41、h installed switch shall be labeled to indicate itsoperation and the circuit controlled.6.8 Wires, Cables, and ClampsWires and cables shall beinspected for adequacy of support, protection, and generalcondition throughout. The desirable and undesirable features inaircraft wiring installations are lis
42、ted in the following andindicate conditions that may or may not exist. Accordingly,aircraft wiring shall be visually inspected for the followingrequirements. (WarningFor personal safety and to avoid thepossibility of fire, turn off all electrical power before starting aninspection or performing main
43、tenance of the aircraft electricalsystem.)6.8.1 Wires and cables are supported by suitable clamps,grommets, or other devices at intervals of not more than 24 in.(61 cm), except when contained in troughs, ducts, or conduits.The supporting devices shall be of a suitable size and type withthe wires and
44、 cables held securely in place without damage tothe insulation. Inspect wire and cable clamps for propertightness. Where cables pass through structure or bulkheads,inspect for proper clamping and grommets. Inspect for suffi-cient slack between the last clamp and the electronic equipmentto prevent st
45、rain at the cable terminals and to minimize adverseeffects on shock-mounted equipment.6.8.2 Mechanical standoffs shall be used to maintain clear-ance between wires and structure. Using tape or tubing is notacceptable as an alternative to standoffs for maintaining clear-ance.6.8.3 Phenolic blocks, pl
46、astic liners, or rubber grommets areinstalled in holes, bulkheads, floors, or structural memberswhere it is impossible to install off-angle clamps to maintainwiring separation. Inspect the EWIS to ensure separationbetween the wire and the hole, bulkhead, floor, or structuralmember.6.8.4 Wires and ca
47、bles in junction boxes, panels, andbundles are properly supported and laced to provide propergrouping and routing.6.8.5 Clamp-retaining screws are properly secured so thatthe movement of wires and cables is restricted to the spanbetween the points of support and not on soldered or mechani-cal connec
48、tions at terminal posts or connectors.6.8.6 Wire and cables are properly supported and bound sothat there is no interference with other wires, cables, andequipment.6.8.7 Wires and cables are adequately supported to preventexcessive movement in areas of high vibration.6.8.8 Insulating tubing is secur
49、ed by tying, tie straps, or withclamps.6.8.9 Continuous lacing (spaced 6 in. (15 cm) apart) is notused except in panels and junction boxes where this practice isoptional. When lacing is installed in this manner, outside ofjunction boxes, it shall be removed and replaced with indi-vidual loops.6.8.10 Do not use tapes (such as friction or plastic tape) thatwill dry out in service, produce chemical reactions with wire orcable insulation, or absorb moisture.6.8.11 Insulating tubing shall be kept at a minimum andshall be used to protect wire and cable from abrasi
