1、AEROSPACE RECOMMENDED PRACTICEARP426 REV.AIssued 1959-02Reaffirmed 2008-02Revised 2001-07Superseding ARP426Compass System InstallationsFOREWORDChanges in this Revision are format/editorial only.TABLE OF CONTENTS1. SCOPE1.1 Purpose2. REFERENCES3. GENERAL REQUIREMENTS3.1 Equipment3.2 Materials3.3 Work
2、manship3.4 Environmental Conditions3.5 Installation Survey and Component Selection4. DETAIL REQUIREMENTS4.1 Mechanical4.1.1 Location and Mounting4.1.2 General4.1.2.1 Mounting Brackets4.1.2.2 Ventilation4.1.2.3 Safety4.1.2.4 Bonding4.2 Electrical4.2.1 Power Supplies4.2.1.1 AC and DC4.2.2 WiringSAE Te
3、chnical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is
4、 the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2008 SAE International All rights reserved. No part of this publication may be re
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6、4-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE ARP426 Revision A- 2 -4.2.3 Shielding and Grounding4.2.4 Switches, Signal Devices, and Interlocks4.2.5 Cockpit Control4.3 Maintenance4.3.1 Accessibility4.3.2 Clearances4.3.3 Replaceability4.3.3.1 Hardware4.3.4 Interchang
7、eability5. TESTS5.1 Mechanical Installation5.1.1 Mounting5.1.2 Electrical Installation5.1.2.1 Dielectric Test5.1.2.2 Continuity5.1.2.3 Visual Inspection5.1.2.4 Power Supply5.1.3 System Adjustments5.1.3.1 Compass Compensation5.1.4 System Operation5.1.4.1 Interlock Check5.2 Flight Test5.2.1 Interlocks
8、5.2.2 Magnetic Heading5.3 Post Flight5.3.1 MechanicalSAE ARP426 Revision A- 3 -1. SCOPE:These recommendations cover the mechanical and electrical installation and installation test procedures for Compass Systems of the type normally used in transport type aircraft. The recommendations in the ARP do
9、not supersede any airworthiness requirements in Civil Air Regulations.1.1 Purpose:This Aeronautical Recommended Practice is intended to outline the minimum requirements for Compass System installation design, performance and test recommendations for use as a guide by the aircraft industry.2. REFEREN
10、CES:1. “Design Manual on Aircraft Electrical Installations“Available from: Aircraft Industries Assn., 610 Shoreham Building, Washington 5, DC2. Specification MIL-W-5088B (ASG)“Installation of Aircraft Wiring“Available from: Commanding Officer, U.S. Naval Air Station, Johnsville, Pennsylvania3. Speci
11、fication MIL-E-7894A (ASG)(Characteristics of Aircraft Electrical Power“Available from: Commanding Officer, U.S. Naval Air Station, Johnsville, PennsylvaniaAttention: Technical Records Division4. Civil Aeronautics Manual, Part 4b“Aircraft Airworthiness“Available from: The Superintendent of Documents
12、, U.S. Government Printing Office, Washington 25, DC5. SAE Aeronautical Standard AS398A and AS399A“Magnetic Compass“Available from: Society of Automotive Engineers, Inc., 485 Lexington Avenue, New York 17, NYSAE ARP426 Revision A- 4 -3. GENERAL REQUIREMENTS:3.1 Equipment:The Compass Systems referred
13、 to herein should conform to Aeronautical Standard AS398A: Direction Instrument, Magnetic, Non-Stabilized Type (Magnetic Compass) and AS399A: Direction Instrument, Magnetic (Stabilized Type).3.2 Materials:Materials should be of a quality which experience and/or tests have demonstrated to be suitable
14、 and dependable for use in aircraft.3.3 Workmanship:Workmanship should be in accordance with high grade aircraft manufacturing practice.3.4 Environmental Conditions:The design of the installation should be such that satisfactory performance may be obtained under all environmental conditions to which
15、 the aircraft may be subjected. Care should be taken that the unit is not placed in a location where it will be subjected to excessive collections of moisture or other foreign matter.Care should be taken to avoid installing units in areas where the airframes vibration characteristics would adversely
16、 affect the compass system unless, however, the units mounting support is designed to dampen or isolate the affect so as to be acceptable in accordance with the equipment manufacturers recommendations.3.5 Installation Survey and Component Selection:The aircraft manufacturer should, to the best of hi
17、s ability with respect to the aircraft design status relative to existing magnetic disturbances within the aircraft, select and combine the necessary components into a comprehensive system which can be expected to perform the desired necessary functions in accordance with AS398A or AS399A, as applic
18、able. Final calibration should be checked and determined on the basis of flight tests of the initial installation.SAE ARP426 Revision A- 5 -4. DETAIL REQUIREMENTS:4.1 Mechanical:4.1.1 Location and Mounting: Transmitter locations should be chosen to preclude, insofar as possible, all magnetic fields
19、other than the earths. A location should be chosen where the transmitter will be least affected by magnetic disturbances created in the aircraft itself. The purpose of making the compass system remote indicating is to permit the installation of the sensitive element in a position where, under all po
20、ssible conditions of operation of the aircraft, the magnetic field will be as nearly as possible that of the undisturbed earths magnetic field surrounding the craft.In selecting a position for the transmitter, the vicinity of ferrous materials should be avoided. Locations near movable ferrous items,
21、 such as control rods, steel turnbuckles, landing gear, or other movable components should be avoided. Locations near baggage compartments, tool chests and storage space are undesirable, as are those near any structure that may change its magnetic characteristics with prolonged service. There should
22、 be no electrical wiring in the immediate vicinity of the transmitter, particularly conductors carrying direct current. If the aircraft uses a ground return system, the structure should be examined to make certain that no great amount of return current is carried in any structural section near the t
23、ransmitter.The various ferrous bodies in the aircraft should be distributed in a balanced formation with regard to the transmitter, insofar as practicable, particularly if it is not possible to isolate the unit from these bodies. If deviations cannot be eliminated by optimum transmitter location, th
24、ey should be limited to 4 in any direction prior to compensation.Direct reading and remote-indicating transmitters should be installed in their normal level position, 1, when the aircraft is in normal flight attitude. The fore and aft line of the sensing elements should coincide with longitudinal ax
25、is of the aircraft, 1. Use of shock mounts is highly undesirable and should be avoided whenever possible; however, shock mounts may be used if absolutely necessary, provided proper precaution is taken to avoid tilt in azimuth of the transmitter. The use of compensators should be avoided if possible
26、by the selected location of the transmitter. The indicators should be located on the instrument panels in such a manner that the index and dial markings are within 30 of the normal line of sight of the pilot, co-pilot or navigator, perpendicular to the instrument panel. The signal amplifier should b
27、e located in an aircraft equipment rack suitably shock mounted if required.SAE ARP426 Revision A- 6 -4.1.2 General:4.1.2.1 Mounting Brackets: All mounting brackets should be designed to provide adequate strength, freedom from vibration and flexing that would interfere with the satisfactory operation
28、 of the Compass System under any flight conditions encountered in service. The material of the platform, support members, mounting screws, mounting locknuts, etc., shall be non-magnetic. (“Stainless steels“ of a magnetic nature should be avoided in this installation.)4.1.2.2 Ventilation: All compone
29、nts should be installed in accordance with the temperature requirements of the instrument. If it is impossible to locate the equipment in an aircraft location which has a temperature similar to that required, then provisions for direct conditioned air to this equipment must be made.4.1.2.3 Safety: A
30、ll attached fittings and fasteners such as bolts, nuts, clevis pins, etc., if not of the self locking type should be locked with safety wire or cotter pins.4.1.2.4 Bonding: The chassis of mounting frames of all components should be electrically bonded to the aircraft structure. All mating surfaces w
31、hich conduct a ground return should be clear of paint, anodized coating or other non-conducting materials.4.2 Electrical:4.2.1 Power Supplies: The design of the electrical installation and the selection of the power supply components should conform to the best aeronautical practice. Intermittent loa
32、ds, other than Compass System, should be carefully considered with regard to the compass system performance.4.2.1.1 AC and DC: Voltages and frequencies supplied to the Compass System should be in accordance with its established design ratings.4.2.2 Wiring: Connections should be made in accordance wi
33、th the wiring diagrams supplied by the compass manufacturer. Power leads and circuit protective devices should be installed in accordance with standard practices or as specified by the compass manufacturer. Electrical cabling and wiring should be adequate to meet such requirements as maximum allowab
34、le voltage drop, lead resistance, and current as specified for the compass installation. References 1 and 2 may be used as a guide for aircraft wiring.4.2.3 Shielding and Grounding: Strict conformance to the shielding specifications supplied by the compass manufacturer is recommended in all installa
35、tions to eliminate any possibility of spurious signals. Where shielding is grounded at specified locations, the signal leads should be enclosed in sleeving to insulate the shielding from other circuits and ground contacts with the aircraft structure.4.2.4 Switches, Signal Devices, and Interlocks: Th
36、ese items should be installed and electrically interconnected into the system, in accordance with the instructions of the compass manufacturer, to insure that adequate protection of the aircraft and the compass system is maintained.SAE ARP426 Revision A- 7 -4.2.5 Cockpit Control: The compass deslavi
37、ng switch, if provided, should be located near the indicator.4.3 Maintenance:4.3.1 Accessibility: Ready access should be provided for service points such as lubrication, adjustment, dehydrators, and other items requiring attention while the compass is installed in the airplane. Units requiring frequ
38、ent replacement should be located to provide for ease of removal. The installation of such units behind stress panels and other units, which require prior removal for access, should be avoided wherever possible. Where units are located behind non stressed panels, the use of quick-fasteners is recomm
39、ended for attaching the panel.4.3.2 Clearances: Adequate clearance should be provided for:(1) Installation of components in the aircraft, through openings and around other items.(2) Normal movement of the unit during flexing of shock mounts.(3) Installation and removal of electrical or mechanical co
40、nnections.(4) The use of tools required for removing and installing attachments.(5) Removing the components completely from the aircraft, through openings and around other items.4.3.3 Replaceability: Location of mounting nuts, bolt holes, and other such fasteners that are required should be governed
41、 by the tolerances of the matching unit being installed. The alteration of a component to match the aircraft fittings should be avoided in the interests of interchangeability. Where shims are required to align the unit they should be attached to and become a permanent part of the aircraft.Use of the
42、 following devices is recommended wherever possible to facilitate replaceability.(1) Vibration-proof nuts.(2) Nut plate attached to mounting brackets.(3) Mounting subplates equipped with quick-fasteners.(4) Electrical disconnect plugs in lieu of terminal strips: however, disconnect plugs should be k
43、ept to a minimum for the low current carrying circuits of the compass system.4.3.3.1 Hardware: The use of standard aircraft hardware is recommended wherever possible. All hardware used to install the transmitter must be non-magnetic.SAE ARP426 Revision A- 8 -4.3.4 Interchangeability: All components
44、of a like type and function should be interchangeable with no further field modifications or internal adjustments at the time the unit is installed.Where external adjustments are required to permit components to be used in different type aircraft or different portions of the system, it is recommende
45、d that instructions for making the adjustment be placed on the unit wherever possible. Where two units appear identical but produce different operating characteristics which, if misplaced, would tend to cause malfunctioning, means should be provided, such as dowel locating pins, or other such device
46、s to physically prevent the components from being improperly installed. Where two or more components, having different functions but possessing identical connectors, are adjacent, means should be provided to physically prevent crossed connections. Each connector cable should be clamped close enough
47、to the proper unit to prevent it from being cross connected to the wrong unit.The use of placards, color coding, and other marking can be used but should not be relied upon for complete protection.5. TESTS:The manufacturers recommendations regarding any special test equipment required, and specific
48、tests to be performed, should be utilized in conjunction with the following:5.1 Mechanical Installation:5.1.1 Mounting: All component mounting bases and brackets should be inspected for security of attachment to the basic structure and the components themselves for security of attachment to their re
49、spective mounting bases.5.1.2 Electrical Installation:5.1.2.1 Dielectric Test: As required to ascertain satisfactory system operation when dielectric failure is suspected.5.1.2.2 Continuity: As required to ascertain satisfactory circuitry when discontinuity is suspected. (Note: To avoid electrical failures due to damaged connectors after continuity checks have been made use an ohmmeter with a receptacle pin or socket soldered on each prod.)NOTE: Never use an ohmmeter to check the transmitter. DC voltage will magnetize and destroy the calibratio
