1、NO FAULT FOUND - A CASE STUDYARINC REPORT 431PUBLISHED: April 1, 1996AN A DOCUMENTPrepared byAVIONICS MAINTENANCE CONFERENCEPublished byAERONAUTICAL RADIO, INC.2551 RIVA ROAD, ANNAPOLIS, MARYLAND 21401This document is based on material submitted by variousparticipants during the drafting process. Ne
2、ither AMC nor ARINChas made any determination whether these materials could besubject to valid claims of patent, copyright or other proprietaryrights by third parties, and no representation or warranty, express orimplied, is made in this regard. Any use of or reliance on thisdocument shall constitut
3、e an acceptance thereof “as is” and besubject to this disclaimer.Copyright 1996 byAERONAUTICAL RADIO, INC.2551 Riva RoadAnnapolis, Maryland 24101-7465ARINC REPORT 431 NO FAULT FOUND - A CASE STUDYPublished: April 1, 1996This Report was prepared for the Avionics Maintenance Conference by Task Group T
4、G 116 on UnverifiedRemovalsPrepared by the Avionics Maintenance Conference Steering GroupReport 431 Adopted by the AMC Steering Group: February 12, 1996Report 431 Adopted by the Industry: March 22, 1996iiFOREWORDActivities of AERONAUTICAL RADIO, INC. (ARINC)and thePurpose of ARINC Reports for Avioni
5、cs MaintenanceAeronautical Radio, Inc. is a corporation in which the United States scheduled airlines are theprincipal stockholders. Other stockholders include a variety of other air transport companies, aircraftmanufacturers and foreign flag airlines.Activities of ARINC include the operation of an
6、extensive system of domestic and overseasaeronautical land radio stations, the fulfillment of systems requirements to accomplish ground and airbornecompatibility, the allocation and assignment of frequencies to meet those needs, the coordination incident tostandard airborne communications and electr
7、onics systems and the exchange of technical information. ARINCsponsors the Avionics Maintenance Conference (AMC), composed of airline maintenance personnel. It is aninformal industry organization serving the needs of the air transport industry in matters of avionicsmaintenance. Its objectives are pr
8、omotion of improved avionics systems and equipment reliability andperformance. It is the medium of exchange of information and ideas between and among users, repair shops,installers, suppliers, manufacturers, and designers of avionics systems, equipment, and components as aprofessional approach to m
9、aintainability and maintenance practices.AMC objectives are effected through industry conferences and informal task groups who work onproblems of mutual industry concern. The services are administered by a Steering Group (composed of airtransport operator personnel in charge of avionics line mainten
10、ance, overhaul shops, and maintenanceengineering) and a Secretariat provided by ARINC.Traditionally, ARINC “Gray Cover” documents have originated within the Airlines ElectronicEngineering Committee (AEEC), another standing committee of ARINC, composed of avionics developmentengineering personnel. AE
11、EC is functionally oriented toward formulation of standards for air transportavionics equipment. Although AMC is primarily a forum for the informal exchange of logistical information,both AEEC and AMC realize that only through AMC effort can needed guidance documents concerningmaintenance engineerin
12、g be prepared because of the increased demand on AEEC for more and more newARINC airborne hardware specifications.It is desirable to reference certain general ARINC Specifications or Reports which are applicable tomore than one type of equipment. These general Specifications or Reports may be consid
13、ered assupplementary to the Equipment Characteristics in which they are referenced. They are intended to set forththe desires of the airlines pertaining to components and general design, construction and test criteria, in order toinsure satisfactory operation and the necessary interchangeability in
14、airline service. The release of aSpecification or Equipment Characteristic should not be construed to obligate ARINC or any airline insofar asthe purchase of any components or equipment is concerned.An ARINC Report (S pecification or Characteristic) has a twofold purpose which is:(1) To indicate to
15、the prospective manufacturers of airline electronic equipment the considered opinionof the airline technical people coordinated on an industry basis concerning requisites of newequipment, and(2) To channel new equipment designed in a direction which can result in the maximum possiblestandardization
16、of those physical and electrical characteristics which influence interchangeability ofequipment without seriously hampering engineering initiative.Final Report of AMC Task Group TG-116 on Unverified RemovalsiiiAMC TG-116MD-80 Proximity Switch Electronics UnitUnverified Removal Task GroupFinal Report
17、ContentsPageSection 1: Introduction and Task Group General Findings 11.1 History of the TG-116 Task Group 11.2 Organization of the Task Group Report 31.3 Task Group Organization and Activities 31.3.1 Task Group Organization 31.3.2 Task Group Investigative Methods 41.3.2.1 The Prioritization of Fligh
18、t Squawks 41.3.2.2 The Use of Airline Maintenance Databases 61.3.2.3 The Symptom/Fix Matrix 71.3.2.4 Data on Removed Proximity Sensors 81.3.2.5 Task Group Participation by Other Vendors 81.4 Task Group Conclusions 91.5 Task Group Lessons Learned 91.5.1 Most NFF problems are system problems 91.5.2 BI
19、T systems need more awareness of system interactions 101.5.3 System problems need a team solution 111.5.4 The importance of clear and accurate technical documentation 111.5.5 Potential problems in the use of ATA codes 111.5.6 Solutions to many NFF problems are alrady known, but not implemented 121.6
20、 Conclusion 121.7 Members of the TG-116 Task Group 131.8 Appendix 1: Description of Proximity Sensors and Proximity Systems 141.8.1 The Proximity Switch System 141.8.2 The Proximity Sensor 141.8.3 Proximity Sensor Failure Modes 161.8.4 Troubleshooting Proximity Sensor Problems 161.8.5 Improved Senso
21、r Troubleshooting Tool 171.9 Appendix 2: MD-80 PSEU Symptom/Fix Matrix for Jan. 90 - Sept. 90 18Final Report of AMC Task Group TG-116 on Unverified RemovalsivAMC TG-116MD-80 Proximity Switch Electronics UnitUnverified Removal Task GroupFinal ReportContents (contd)PageSection 2: Technical Findings, C
22、orrective Action and Recommendations 232.1 Stall Indication Failure 252.2 Slat Disagree 342.3 Autoslat Fail 432.4 Autospoiler “Do Not Use” 462.5 Spoiler Deployed 492.6 Rudder Travel Unrestricted 512.7 Main Gear Unsafe 532.8 Nose Gear Unsafe 552.9 Gear Door Open 592.10 Door Warning (except Cargo Door
23、) 612.11 Cargo Door Warning 622.12 Landing Gear Aural Warning 65Final Report of AMC Task Group TG-116 on Unverified Removals1Section 1Introduction, and Task Group General Findings1.1 History of the TG-116 Task GroupAn issue of great concern to the avionics maintenance community is that of unverified
24、 or “No Fault Found” removals(NFF). 1 The NFF removal refers to electronic equipment removed from an aircraft during maintenancetroubleshooting, which, when returned to the manufacturer, is tested and found to work correctly, and issubsequently returned to the airline marked “No Fault Found.” The fa
25、ct that, despite the airline industrys pastefforts, some 50% of all equipment removals continue to be reported as NFF, justifies a determined effort tounderstand the root causes and identify solutions to this tremendously wasteful problem. The AMC TG-116 TaskGroup was formed with that purpose in min
26、d.The initial concept to form an NFF study team originated with ELDEC Corporation. ELDEC has manufacturedproximity switch electronics units (PSEU) and proximity sensors for more than 30 years. This type of equipment isinstalled on virtually every type of transport and military aircraft. Although the
27、 NFF rate for PSEU equipment isabout equal to industry average, in 1988 we received a high level of communication from MD-80 operators about theNFF rate on that aircraft model. ELDEC management therefore agreed to a proposal from myself to initiate anactivity to address the problem. This decision le
28、d to the formation of an investigative team consisting of engineersfrom ELDEC, McDonnell Douglas, and from the maintenance engineering staffs of several airlines.The decision to seek support from ARINC and the AMC (Avionics Maintenance Conference) Steering Group wasinspired in part by an article on
29、the NFF problem published in the May/June 89 issue of Plane Talk entitled “TheBlack Hole in Avionics Maintenance.” In a call for concerted industry action, the article concluded with the appeal,“The sooner we bring the problem into the open, the faster unconfirmed removalswill be relegated to a foot
30、note in the avionics history books.”ELDEC proposed to focus exclusively on the MD-80 aircraft. The MD-80 PSEU is an early system with a relativelyhigh NFF rate, and one of the first PSEUs with a microprocessor system capable of storing in-flight faultinformation. The aircraft is also a mature platfo
31、rm with an established performance history. Our hypothesis was that,by thoroughly studying the NFF problem of one particular avionics system, we might develop insights into thegeneric causes of the NFF problem, which could benefit the AMC community as a whole.ELDEC approached the AMC Steering Group
32、with its idea in 1989. The Steering Group supported the proposal andrequested that the Task Group formed by ELDEC (AMC Task Group TG-116) should present its findings to theentire AMC and should attempt, where possible, to draw conclusions applicable to the industry at large. Althoughsome concerns we
33、re expressed about the teams narrow focus, we believe in retrospect that the approach was correct.Had we broadened our investigation to include other equipment, we would never have reached the level of root causetechnical investigation necessary to actually solve problems.The Task Group met once in
34、early 1990, and completed its formal activity fifteen months later. A kickoff review ofits planned investigative strategy was presented before the 1990 Atlanta AMC. Several interim report excerpts werepublished during 1990 - 91. 2 An overview of Task Group activity was also presented to a Douglas co
35、nference of its1 Other common industry synonyms for No Fault Found removals include No Trouble Found (NTF), Unconfirmed,Could Not Duplicate (CND), and Unverified removals.2 John Ardussi, “No Fault Found Removals - A Vendors Perspective,” Plane Talk, April 1990; John Ardussi John Ardussi, “Unraveling
36、Unverified Removals - The Final Chapter,” Plane Talk, April 1991; Danna K. Henderson, “Those SquawkingBlack Boxes,” Air Transport World, Nov. 1991, pp. 90 - 93.Final Report of AMC Task Group TG-116 on Unverified Removals31.2 Organization of the Task Group ReportThe following report is divided into t
37、wo sections.Section One. Section One is an overview of Task Group TG-116 organization, activities and conclusions. Itspurpose is to fulfill the request of the AMC Steering Committee to address the broader issue of unverified removals,for the benefit of the industry as a whole. It therefore contains
38、general conclusions, “lessons learned,” andrecommendations for consideration by the industry, based on the detailed work described in Section Two. Thissection also contains a brief technical description of the operation of PSEU equipment, as background to the detailedMD-80 investigations reported in
39、 Section Two.The Task Group conclusions and recommendations in Sec.1.4-5 can be read independently of Section Two, and donot require a technical understanding of the MD-80 aircraft. These findings and recommendations are a summary ofthe teams approximately 1,500 man hours of discussion and debate on
40、 the subject of unverified removals (and anequal amount of home work at our respective places of business). Although these findings are the result of a studyfocused on a single avionics system, we believe that the results have wider applicability, and are offered here forconsideration and discussion
41、 by the avionics community at large.Section Two. Section Two contains detailed technical findings and recommendations affecting primarilyoperators of MD-80 equipment. This is the heart of the report, and represents the area of most intense team effort.Some of the findings will require service bullet
42、ins, maintenance manual changes, and other actions by DouglasAircraft. Once these are completed, we feel confident that operators who implement the recommendations listed inSection Two will experience substantially reduced NFF removals of MD-80 PSEU equipment. Similarly, airframeand LRU manufacturer
43、s who study this section may find information which will help them to design future productsless likely to produce NFF problems.1.3 Task Group Organization and Activities1.3.1 Task Group OrganizationIn addition to ELDEC, the Task Group was made up of airlines who had expressed ongoing NFF problems w
44、ith thesystem under study, and who agreed to support the effort for its duration. The participating airlines includedContinental Airlines, Swissair, TWA and USAir. SAS joined midway through the activity. Douglas Aircraftsupported the effort with Customer Service engineers representing the technical
45、areas of electrical systems, hydro-mechanical systems, avionics engineering and maintenance analysis.The most important factor affecting the successful outcome of the Task Group was having individual participantswhose regular work responsibilities involved direct dealing with the problems in questio
46、n. We found over the courseof the project that we needed input from various airline departments, including line maintenance, maintenanceengineering, maintenance control, and avionics repair. The Task Group was extremely fortunate to have industryparticipants with many years of intimate experience wi
47、th the entire airplane and its systems.Sustained management support was another requirement. Each meeting required travel and expenses for theparticipating companies, as well as the absence of key employees from their regular work. Without managementsupport of each participating organization, it wou
48、ld have been difficult or impossible to put all the pieces together.Even so, the fact that Task Group activities represented “extra” work for every team member did lead to someproblem in continuity of personnel and activity. Companies contemplating the establishment of similar teams shouldnot undere
49、stimate the level of effort needed to achieve meaningful results.The full Task Group met five times, once at each of the team participants in the US. A three-day kickoff meeting washeld at McDonnell Douglas. Each subsequent meeting lasted two days. ELDEC chaired the meetings, and providedongoing coordination and administrative support.Final Report of AMC Task Group TG-116 on Unverified Removals4The first meetings brain storming session resulted in the development of a set of fish bone diagrams (describedbelow) , which provided an initial technical hypothesis and
