1、AEROSPACE INFORMATION REPORTAIR1266REV.AIssued 1977-08Revised 1993-11ReaffirmedFault Isolation in Environmental Control Systems of Commercial TransportsTABLE OF CONTENTS1. SCOPE .31.1 Purpose32. REFERENCES .32.1 Definitions 43. GENERAL FAULT ISOLATION INFORMATION.63.1 Purpose of ECS Fault Isolation6
2、3.1.1 Historical Problems 63.1.2 Impact of Fault Isolation.73.1.3 Purpose of Fault Isolation Equipment 83.2 Fault Isolation System Design83.2.1 Fault Isolation Design Principles93.2.2 Total System Tradeoff Analysis103.2.3 System Fault Isolation Analysis (FIA) and Final Design 193.2.4 Design Limits V
3、ersus Acceptable Operating Limits203.2.5 Concept Integration (Interfaces).213.2.6 Hardware Considerations.213.2.7 Other Considerations .233.3 Demonstration of Specification Compliance 263.3.1 Prototype Verification .263.3.2 Qualification Testing.263.3.3 Initial Airline Service Period .264. FAULT ISO
4、LATION HARDWARE DESIGN EXAMPLES284.1 Manual BITE Example .284.1.1 Subsystem Operation Description282011-06SAE Technical 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 i
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8、dards/AIR1266ASAE AIR1266 Revision A- 2 -TABLE OF CONTENTS (Continued)4.1.2 Fault Isolation Preliminary Design Analysis .324.1.3 Design Implementation 334.2 Automatic BITE Example .394.2.1 Hardware Design .394.3 Automatic BIT With Central Maintenance Computer Example 434.3.1 ACC to CFDIU Interfaces.
9、484.3.2 CFDIU Command/Display Functions .484.3.3 ACC Displays on the CFDU.485. FUTURE TRENDS IN FAULT ISOLATION EQUIPMENT.52SAE AIR1266 Revision A- 3 -1. SCOPE:This SAE Aerospace Information Report (AIR) outlines concepts for the design and use of fault isolation equipment that have general applicat
10、ion. The specific focus is on fault isolation of environmental control systems (ECS) in commercial transports. Presented are general fault isolation purposes, design principles, and demonstration of compliance criteria. These are followed by three design examples to aid in understanding the design p
11、rinciples. Future trends in built-in-test-equipment (BITE) design are discussed, some of which represent concepts already being implemented on new equipment.1.1 Purpose:This AIR provides a practical guide for the design and use of fault isolation systems for the ECS in commercial transports.Airframe
12、 manufacturers may use this AIR for guidance in developing practical, efficient, and workable ECS fault isolation equipment. Equipment suppliers may use this AIR for guidance concerning their role with airframe manufacturers in the development and with the operators in the use of effective ECS fault
13、 isolation equipment. Operators may use this document to write future ECS fault isolation specifications against which the performance of the delivered system can be measured quantitatively. They may also obtain guidance for making more effective use of existing systems.2. REFERENCES:AiResearch Manu
14、facturing Company, “Environmental Control Systems Fault Isolation“. Report 70-7022, 1970, Los Angeles, CaliforniaAlbert, John, “Computerized Maintenance for Aircraft Environmental Control Systems“. Presentation to SAE AC-9 Committee Meeting, Miami, October 1973ARINC Report 604-1, “Guidance for Desig
15、n and Use of Built-In-Test-Equipment,“ September 30, 1988ARINC Report 612, “BITE Glossary,“ December 18, 1986ARINC Report 624, “Design Guidance For Onboard Maintenance System (OMS),“ August 26, 1991Curtis, George C. and Elgin, Charles F., “The MAC MADAR System: An AIDS Model for Commercial Airlines“
16、. Paper 710425 presented at SAE National Air Transportation Meeting, Atlanta, May 1971Douglas Aircraft Company, “Description of ARINC 624 Onboard Maintenance System,“ August 22, 1990Douglas Aircraft Company, “DC-10 Fault Isolation“. Douglas Service, November 1970Douglas Aircraft Company, “Fault Isol
17、ation Analysis (FIA)“. Report DAC67297B, June 1969SAE AIR1266 Revision A- 4 -2. (Continued):Douglas Aircraft Company, Flight Development Group, “Finding Faults with FEFI“. DC Flight Approach, Second Quarter 1970Hamilton Standard, “Hamilton Standard Guidelines for Airborne Integrated Data Systems“, R
18、eport HSPC 70E20, 1970Hawkins, Capt. F. H. and Vermeulen, H. C., “Aircraft Integrated Data Systems - a Review of Their History and Current Status“. Shell Aviation News, No. 401-19712.1 Definitions:AIRCRAFT INTEGRATED DATA SYSTEM (AIDS): A term (adopted by ARINC) in general use for airborne recording
19、 systems that include acquisition and signal conditioning.AUXILIARY POWER UNIT (APU): An on-aircraft unit, usually a gas turbine, that supplies an auxiliary air source for the ECS and auxiliary electrical power generation.AUTOMATIC TEST EQUIPMENT (ATE): General purpose, usually computerized test equ
20、ipment that when connected to the unit under test through the necessary interface, automatically performs acceptance testing.BUILT-IN-TEST (BIT): Tests performed by the system upon itself for the purpose of detecting faults, annunciating fault conditions, isolating faults, and possibly taking correc
21、tive action.BUILT-IN-TEST-EQUIPMENT (BITE): That part of a system, usually sensors, electronics and display, that are used as a tool to supplement maintenance procedures for isolating system faults.CENTRALIZED FAULT DISPLAY INTERFACE UNIT (CFDIU): A unit (part of the CFDS described by ARINC 604) whi
22、ch interfaces aircraft operational subsystems to the display unit (CFDU).CENTRALIZED FAULT DISPLAY SYSTEM (CFDS): A system described by ARINC 604 that uses a centralized fault command/display terminal to retrieve and display subsystem produced BITE display data.CENTRALIZED FAULT DISPLAY UNIT (CFDU):
23、 A unit (part of the CFDS described by ARINC 604) which provides the actual display interface for the maintenance crew.ELECTRICALLY ALTERABLE READ-ONLY MEMORY (EAROM): Nonvolatile computer memory devices whose memory content can only be changed by application of an electrical signal.ELECTROMAGNETIC
24、INTERFERENCE (EMI): Electromagnetic phenomena which, either directly or indirectly, can contribute to a degradation in performance of an electronic receiver or system.SAE AIR1266 Revision A- 5 -2.1 (Continued):ENVIRONMENTAL CONTROL SYSTEM (ECS): That aircraft equipment responsible for maintaining pr
25、oper cabin ventilation airflow, temperature, and pressure. It usually comprises engine air source control; air conditioning packs and their control; cabin inflow, ventilation, and temperature control; and cabin pressure control. It sometimes includes avionics, cargo, and galley ventilation and tempe
26、rature control.FAILURE MODE AND EFFECT ANALYSIS (FMEA): An analysis of a particular design for describing, as a minimum, the most probable ways an equipment can fail and the consequences of such failure.FAULT ISOLATION: The process and actions, following equipment failure, that are involved in the i
27、dentification of the unit, assembly, or piece part that has failed.FAULT ISOLATION ANALYSIS (FIA): A systematic evaluation of failure causes, indications and probabilities to determine the level of Fault Isolability provided for in the system design.GROUND SUPPORT EQUIPMENT (GSE): As used in this re
28、port, it is ground-based equipment not carried on-board the aircraft that is used to inspect, test, or troubleshoot aircraft equipment.LINE REPLACEABLE UNIT (LRU): A component or assembly of components that by design, is packaged to be removed and replaced as a single item.MEAN-TIME-BETWEEN-FAILURES
29、 (MTBF): A measure of actual hardware reliability, determined by summing operating time on all units and dividing by the number of confirmed failures.MEAN-TIME-BETWEEN-UNSCHEDULED-REMOVALS (MTBUR): A measure of apparent hardware reliability or actual operational reliability, determined by summing op
30、erational flight time on all units and dividing by the number of unscheduled and unplanned unit removals, regardless of cause.MINIMUM EQUIPMENT LIST (MEL): Refers to the minimum aircraft system hardware that must be operational prior to safe aircraft dispatch. Appropriate procedural limitations may
31、be enacted to account for inoperative equipment to maintain safe, airworthy operation.ON-BOARD MAINTENANCE SYSTEM (OMS): A system described by ARINC 624 that provides a centralized location on the aircraft for electronically furnishing all the aircraft maintenance information.RANDOM ACCESS MEMORY (R
32、AM): Volatile computer memory devices whose read/write memory content is only active while electrical power is applied.READ-ONLY MEMORY (ROM): Nonvolatile computer memory devices whose contents can only be read, not written in normal operation. The memory contents remain intact with or without power
33、 applied.SAE AIR1266 Revision A- 6 -2.1 (Continued):ROOT-MEAN-SQUARE (RMS): A calculation of the square root of the summation of the squares of individual variables or constants. In this report it is used to determine practical system-level tolerances composed of more than three component tolerances
34、.3. GENERAL FAULT ISOLATION INFORMATION:This section first discusses the purpose of ECS fault isolation. The design of an effective fault isolation system is then discussed followed by criteria for demonstrating compliance to fault isolation specification requirements.3.1 Purpose of ECS Fault Isolat
35、ion:The primary purpose of fault isolation is to minimize the total cost of aircraft maintenance by reducing flight delays, out-of-service incidents, and spares requirements.Commercial jet transports represent a large investment both to the airlines and airframe manufacturers. The airlines have a hi
36、gh investment in direct costs of the aircraft and in costs of flight delays due to the large number of passengers carried per aircraft. The airframe manufacturers (and their subcontractors) have a large investment in guarantees on unscheduled removals of components from the aircraft in service. To e
37、nsure safety of flight and to protect these investments, it is important that the flight and ground crews be able to identify an improperly operating aircraft system and that ground crews can isolate and correct the malfunctioning component(s) as quickly as possible with a high level of confidence.
38、To reduce flight crew workload, fast, accurate identification of faults in primary systems is required so that appropriate crew alerts can be provided and backup system(s), either automatic or manual, can be employed with a minimum of flight crew effort. This requirement to minimize crew workload ha
39、s special importance for two-man crew operations.A systematic method of fault isolation is required to assure the needed speed and accuracy of fault identification. Historical problems have produced the need for fault isolation methods and equipment on-board the aircraft that operates quickly, accur
40、ately, and requires the minimum of maintenance crew training.3.1.1 Historical Problems: Historical discussion of past fault identification problems is necessary to better recognize the need for accurate, reliable, and readily available fault isolation procedures and equipment.Historically, the major
41、 problem areas aggravating the high cost of aircraft maintenance are:a. Excessive time to properly isolate system faultsb. Excessive unscheduled removal of line replaceable units (LRUs) which are not faultyc. Excessive time required to remove many LRUsSAE AIR1266 Revision A- 7 -3.1.1.1 Excessive tim
42、es to properly isolate faulty components are caused by several factors in the absence of effective on-board fault isolation equipment:a. Inexperienced ground crewb. Ground support equipment (GSE) to aid the ground crew not availablec. GSE not functioning properlyd. Ground crew unfamiliar with GSE op
43、eration (takes too long to set up and operate)e. Maintenance manuals (publication software) not readily accessiblef. Maintenance publications incomplete, unwieldy or out of date3.1.1.2 Erroneous LRU removal rates among airlines are widely varied with respect to several factors. For example, ECS mech
44、anical LRUs removed for no cause typically run from 15 to 20%; Electrical units incorrectly removed have run at 50% or more; APU controllers on some aircraft apparently removed for no cause have run at about 80%; cabin temperature controllers apparently removed for no cause run from 80 to 90%. The e
45、rroneous removal rates of refrigeration units which are physically large is typically low because sufficient troubleshooting time has to be spent to ensure that the unit being pulled is actually faulty. All of these cases involve systems with no on-board fault isolation equipment.Electronic units su
46、ch as the cabin temperature or auxiliary power unit (APU) controller are relatively easy to remove. Almost any cabin temperature or APU problem is, therefore, likely to be treated first by replacing the controller. For aircraft without fault isolation systems this easy accessibility contributes to h
47、igh erroneous removal rates.3.1.1.3 Excessive time to remove the faulty component involves accessibility and removal ease of each LRU. Historically, these factors have seldom received adequate consideration in the overall system design. Difficulty in reaching and replacing certain LRUs has resulted
48、in delays or, more frequently, unduly long down time. Positive, accurate fault isolation of these hard-to-replace components is required so that time consuming replacements are not made in error. Although they have a secondary impact on fault isolation, the subjects of accessibility and removability
49、 will not be discussed in further detail.3.1.2 Impact of Fault Isolation: Fault isolation has an impact on aircraft dispatchability and maintainability as well as airline spares provisioning.3.1.2.1 Dispatchability: Dispatchability or dispatch reliability of aircraft is very important for the airlines operating on a regularly scheduled basis. Dispatch delays of any aircraft with a load of passengers can be very expensive if rescheduling of other aircraft is involved.Good dispatch reliability requires the proper fault isolation of malfunctioning equipment as w
