t7,PROCEEDINGS
`
`OF THE
`
`AIAA/IEEE
`
`6th
`
`/iDIGITAL AVIONICS
`
`SYSTEMS CONFERENCE
`
`DECEMBER 3-6, 1984/ BALTIMORE, MARYLAND
`
`AMERICAN INSTITUTE OF
`AERONAUTICS AND ASTRONAUTICS
`. • TECHNICAL COMMITTEE
`- DIGITAL AVIONICS
`
`INSTITUTE OF ELECTRICAL
`AND ELECTRONIC ENGINEERS
`• -AEROSPACE AND ELECTRONICS
`SYSTEMS SOCIETY
`.
`
`•
`
`BOEING
`Ex. 1013
`
`

`
`REMOTE MAINTENANCE MONITORING USING A DIGITAL DATA LINK
`
`84-2677
`
`Drew Dowling*
`Richard A. Lancaster
`
`ARINC Research Corporation
`Annapolis , Maryland
`
`Abstract
`
`The purpose of this paper is to present a concept
`for upgrading the military aircraft maintenance
`approach in the future . The evolution of digital
`avionics in both military and commercial aircraft
`is creating changes that affect today ' s approach
`to maintenance . Commercial aviation has made sig-
`' nificant progr ess in the direction of maintenance
`monitoring usi ng a digital data link . This paper
`presents the s_tatus of maintenance-monitoring
`efforts within the commercial airlines and , rec-
`' ognizing the differences that exist between the
`military and commercial application, proposes an
`• aircraft maint enance concept for the military in
`the 1990s .
`
`' ·,
`
`Background
`
`The sophistication of new aircraft systems cur(cid:173)
`~' rently being developed suggests that a new mainte(cid:173)
`' nance approach may be needed . The employment of
`; auilt-In Test (BIT) in avionics Line Replaceable
`~ Units (LRUs) to isolate faults can reduce the
`~ organizational maintenance activity to replaclng
`L' designated components at a low-skill level. The
`~ isolation of faults not identified with BIT can
`··typically involve sophisticated and expensive
`;' Automatic Test Equipment (ATE) and highly skilled
`technicians or engineers. With the trend toward
`, increased packing density on printed circuit
`~ boards, and in turn, on Shop Replaceable Units
`~ (SRUs), the cost of these units is escalating.
`~. All of the above factors contribute toward poten(cid:173)
`;· tially high maintenance costs in the AVionics
`/ Intermediate Shop (AIS).
`In an austere budget
`} 1 e~vironment the maintenance activity is subject
`~ to budget cuts , resulting in reduced maintenance
`~ capability. This situation presents a critical
`:: problem in an environment wheTe command emphasis
`is placed on operational readiness.
`In response
`to this probl em, operational availability projec(cid:173)
`; tions have become increasingly important to sys-
`tems under development; however, this is often
`•. translated i nto achieving improved reliability of
`~ the system. The maintenance approach has a sig(cid:173)
`~- nificant influence on the downtime, and extended
`~ periods of downtime will affect operational
`~ availability more than poor reliability .
`,:
`il-
`'
`~~' Before proceeding with the discussion of a main(cid:173)
`! tenance concept for the 1990s, it is appropriate
`~· to present some of the conc~pts that characterize
`·· current military aircraft maintenance . Flight
`operations, maintenanceJ and logistics are sepa(cid:173)
`~ rate entit i es within fhe military. The AIS at
`• ~ing level supports the operations of the wing,
`~ and the logistics or supply activity supports
`~- the AIS. Each of these activities .(operations ,
`~ l. **~M-=-em-:b-e-r~I--E--E~E •
`~
`
`maintenance, and supply) operates independently
`through the use of separate communications
`facilities.
`
`Each operational aircraft wing is self-sufficient
`with intermediate-level maintenance capabilities.
`Avionics maintenance capabilities include exten(cid:173)
`sive automatic test equipment to fault-isolate
`both LRUs and SRUs. The Air Force intermediate(cid:173)
`level maintenance facility currently requires 4500
`square feet of air-conditioned space; therefore,
`dispersal of the maintenance facility to forward
`operating bases presents major problems. With
`the increased sophistication of aircraft in the
`1990s , the Air Force intermediate-level mainte(cid:173)
`nance shop may become even larger, more costly,
`and less mobile . As a result of these factors,
`it is the objectives of this paper to suggest
`that a new maintenance concept for aircraft may
`be appropriate for the 1990s.
`
`On-Condition Maintenance Monitoring
`for Commercial Aircraft
`
`Haintenance of aircraft used by the commercial
`airlines is regulated by the Federal Aviation
`Administration . The airline companies may
`perform preventive maintenance at scheduled
`intervals or they may conduct preventive
`maintenance by replacing engine components at
`specified performance thresholds . Many of the
`airline companies adopt the second approach as
`the most cost-effective from the standpoint of
`maintenance and loss of revenue because of air(cid:173)
`craft unavailability. The performance threshold
`approach requires a system to monitor performance
`thresholds such as temperature, pressure , and
`fuel consumption during normal engine operation.
`This on-condition ~onitoring capability evolved
`from the Aircraft Integrated Data System (AIDS)
`developed primarily for flight safety purposes in
`the early 1970s. Monitored data were analyzed to
`identify components requiring maintenance. Row(cid:173)
`ever, the analysis was conducted off line, which
`introduced significant delays between recording
`of the data and the preventive maintenance action
`to replace components.
`
`In 1979 some of the airlines pioneered in trans(cid:173)
`mitting the on-condition monitoring data to ground
`facilities for immediate analysis to identify
`components that should be scheduled for replace(cid:173)
`ment. This approach is being used today by TWA,
`Delta , and United Airlines for scheduling mainte(cid:173)
`nance on the DC-9, the Super BO, and the 757/767
`aircraft . The ARINC Communications Addressing
`and Reporting system (ACARS), augmented with an
`auxiliary terminal, is used for transmission of
`tne data (see Figure 1). Typically, engine(cid:173)
`monitoring data are transmitted at 5-minute
`
`Copyright@ 1984 by AR INC Research Corporation. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission.
`
`Released 10 AlA A lo publish In a ll forms.
`
`503
`
`BOEING
`Ex. 1013
`
`

`
`131.55
`
`131 .55
`
`Data Link
`
`Flight Control
`Operations
`Crew Scheduling
`Aircraft M aintenance
`Downline Stations
`Reservations
`Freight
`MIS
`Other
`
`A CARS
`Stat ion
`
`ACARS
`Stat-ion
`
`Switched
`Network
`ESS
`
`Control
`Processor
`AFE PS
`
`2400 BPS
`Data Circuit
`
`· ..
`··•
`, ,,
`
`Fig. 1 ARI NC communications Addressing and Report ing System (ACARS)
`
`intervals during a climb and 30-minute intervals
`during crui se . A single VHF channel (131 . 55 MHz)
`is used by ACARS for transmission of digital
`information. Maintenance-monitoring data repre(cid:173)
`sent only 15 percent of the current digital traf(cid:173)
`fic load; however , this will increase as more air(cid:173)
`lines implement r emote maintenance monitoring .
`Once r eceived a t the ground station , these data
`are analyzed to determine the subsyst ems r equiring
`repl acement . The aircraft fligh t schedul e is t hen
`analyzed t o determine t he appr opr iate l ocation to
`accomplish preventive maintenance with a mi nimum
`disruption of oper ations.
`
`Concept for Avionics Interconnected
`Maintenance System (AIMS)
`
`The airline community is now considering an expan(cid:173)
`sion of its aircraft maintenance concept . Aero(cid:173)
`nautical Radio , Inc ., has proposed a concept for
`using ACARS t o t ransmit avionics fau l t information
`derived from BIT data . The concept, illustrat ed
`in Figure 2 , is to format BITE (}) r esults into an
`
`ACARS ~ message and transmit the message to
`ground maintenance control whenever a system
`failure occurs. Ground maintenance analyzes the
`data with an "expert system• {2) that emulates
`the diagnostic logic of the maintenance engineers
`to diagnose faults . ~hould additional data be
`required , query messages are sent to the aircraft
`unti l a diagnosis is made . Once the diagnosis of
`the faul t is completed , flight operations ~ is
`quer i ed fo r a flight plan and a schedule is estab(cid:173)
`l ished to perform the requi r ed main tenance . The
`~ropriate mai ntenance activi t y (line station)
`~ is notifi ed of scheduled maintenance , stores
`(supply) ~ is notified of the required compo(cid:173)
`nent, and the Avionics Test Shop {!) is notified
`of the fault condition of the LRU oeing replaced.
`Finally , a data base file that recor ds the mainte(cid:173)
`nance activity is updated ~ ·
`
`Military Maintenance Monitoring
`
`The mili t ary has pursued on-condition monitoring
`i n parallel wi th the commercial ai rl i nes . The
`
`G)
`@
`ACARS ~ ACARS
`
`Aircraft
`
`t-----'8'-IT_E__,
`
`Line Station
`
`Ground
`
`ATS
`
`Shop
`
`Fig . 2 Airlines Concep t f or Avionics Inter connected Ma i ntenance Syst em (AIMS)
`
`504
`
`BOEING
`Ex. 1013
`
`

`
`~;~
`~ ..
`~~ ..
`;,.•. first effo r t in on-condition monitoring was with
`~- the C-SA a i rcraft . The Malfunction, Analysis,
`~ oetection, and Recording System (MADAR) monitored
`~::· more than engine performance [ 1,100 test points~
`including a vionics, engine vibration, pressure,
`l
`temperatur e , and airframe stress (1)], Initially,
`the monito red data were transmitted to ground
`·,,
`~- stations for processing. Difficulties with work(cid:173)
`~: load durin9 missions and the quality of the data
`}~ forced a modification of the system to replace
`.:·· the direct data transmission with a recorder and
`;~--: off-line p r ocessing wi.th a human quality control
`.; interface . over the years this system was used,
`~; and an extensive data base of recorded performance
`;i information was established .
`i .
`f; A more recent effort in on-condition monitoring
`~: is the Turbine Engine Monitoring System (TEMS)
`~: for the A- 10/TF-34 engine . This program consists
`:,· · of in-flight and ground hardware to sense and ana(cid:173)
`,.
`lyze engine parametric data for fault detection ,
`isolation, ·and trending. Currently, the Air
`Force is comple ting a Squadron Integration Pro(cid:173)
`\.! gram that will integrate the TEMS capabilities
`into . the maintenance and logistics capabilities
`for the A- 10/TF-34 engine before operational
`implementation of the system. TEMS is comple-
`'•
`'· • mented by t~e Comprehensive Engine Management
`System (CEMS), which is a ground-based system
`that supports the engine management community
`'· with trend analysis of performance data, engine
`sta tus, and inventory control. Although TEMS
`will interface with CEMS, there apparently is no
`serious c o ~sideration being given to transmitting
`TEMS data to CEMS ground station via a data link.
`Additional information on the TEMS concept is
`available i n References 2 and 3. The Navy has a
`comparable program for engine monitoring for the
`A-7 aircr aft, r eferred to as the Engine Inte(cid:173)
`grated Consolidated Maintenance System (EICMS).
`
`The military implementation of on-condition moni(cid:173)
`toring pr esents a different scenario than the
`airline implementation . Commercial aircraft will
`normally fly standard routes with minimal change
`in engine cond i tions, whereas military aircraft
`engines are subject to continual change in engine
`condition. This presents difficulty in estab(cid:173)
`lishing a basel ine for on-condition monitoring.
`The military has, however~ supported on-condition
`monitoring as part of reliability-centered main(cid:173)
`tenance . * To i mplement this policy there is an
`Integrated Turbine Engine Monitoring System
`(I TEMS) be ing initiated to expand the TEMS con(cid:173)
`cept to new eng ines under development.
`
`Central I ntegrated Test System (CITS)
`
`The B-1 a i rcraft also has a planned in-flight
`engine per formance monitoring system as part of
`the CITS. The engine monitoring does not encom(cid:173)
`pass the s ophistication of TEMS (primarily time
`and temperature data) but does include mainte(cid:173)
`nance mon i toring of avio.nics subsystems. Failed
`subsystems are identified with BIT and the infor(cid:173)
`mation dis played for air crews. Data from CITS
`are recorded for later analysis using ground
`maintenance facilities.
`
`*Reliabili ty-centered maintenance is a mainte(cid:173)
`nance concept that allows the condition of the
`equipment to dictat'e the 'need for maintenance or
`the extent of repair reguired.
`
`F/A-18 Avionics Fault Tree Analyzer (AFTA)
`
`The Navy's new digital F/A-18 aircraft empl oys
`extensive BIT for avionics. Many of t he F/A-18
`avionics subsystems have gone beyond the require(cid:173)
`ment to isolate faults to WRAs (Navy equivalent
`of LRU) and are actually providing data to iso(cid:173)
`late to SRA (Navy equivalent of SRU), The mis(cid:173)
`sion computer is used to integrate the BIT data
`for all WRAs into fault messages that are main(cid:173)
`tained in processor memory. A flight-line tester,
`referred to as the Avionics Fault Tree Analyzer
`(AFTA), has been developed to access and analyze
`the BIT data (4) , The analyzer serves as an
`• exper t system• that conducts a diagnostic analy(cid:173)
`sis emulating an experienced maintenance techni(cid:173)
`cian in order to isolate a fault to the SRA level.
`Although the AFTA is currently ground support
`equipment, the functions performed could be incor(cid:173)
`porated into the airborne processor or in a ground
`system with fault data transmitted to the ground
`station using a data link,
`
`A Proposed Maintenance Concept
`Using a Data Link
`
`Although the concept of using a data link for on(cid:173)
`condit ion engine monitoring has not been adopted
`within the military to date, there seems to be
`sufficient motivation for considering this
`approach for the 1990s. Figure 3 illustrates a
`concept for remote maintenance monitoring that
`integrates both engine monitoring and avionics
`fault analysis with ground processing facilities
`using a data link. The proposed aircraft system
`in Figure 3 incorporates the capabilities of the
`F/A-18 AFTA integrated with the on-board computer.
`The AFTA currently is a passive device · that has
`been designed to analyze the results of BIT data.
`To facilitate isolating faults to the SRU level,
`it may be necessary to augment AFTA with a lim(cid:173)
`ited capability to generate test signals . The
`mission computer would provide the interface
`between the on-board fault analyzer (AFTA) and a
`data link to the ground maintenance system. Avi(cid:173)
`onics fault and engine-monitoring data would be
`formatted into maintenance messages for transmis(cid:173)
`sion over a data link . Messages from ground main(cid:173)
`tenance facilities requesting additional data
`would be processed by the mission computer, which
`issues appropriate commands to the fault analyzer.
`
`The concept of operation for providing mainte(cid:173)
`nance status information to ground stations would
`be to initia~ly transmit baseline information at
`the beginning of a mission. Subsequent messages
`would be sent only when the status changes out(cid:173)
`side preset limits. The volume of data for this
`type of operation would place minimal demand on a
`data link system. Should further system design
`reveal that ground communi cations facilities
`would not be within range of aircraft, the system
`could store data and provide a "dump• of monitored
`data when aircraft are withi~ range of a ground
`station .
`
`The g~ound system centers around the AIS mainte(cid:173)
`nance facility but includes interfaces with both
`flight operations , specialized repair centers
`(SRCs), and the supply system. The avionics
`fault data will be analyzed to identify SRAs
`needing replacement. Expert systems supported by
`highly trained technicians at SRCs will query t he
`mission computer for additional diagnostic
`
`505
`
`BOEING
`Ex. 1013
`
`

`
`LRU
`
`LRU
`
`LRU
`
`Engine
`Monitor
`
`Mission
`Computer
`
`Fault
`Analyzer
`
`AIS
`
`Aircraft
`Subsystem
`
`- - .- - --,
`r
`I
`I
`I
`I
`I
`Data ~ Link
`Modem I' --
`I
`r-~~---~----Gro~ ~
`,,
`·Subsystem I
`I
`II
`t
`I
`I
`L ______ - - - - - - _jl
`I
`I
`I
`I
`I
`SRCs
`I
`__ ::J
`L
`
`Operations
`
`Depot
`
`CEMS
`
`-- --.- -- -- - -
`
`Fig. 3 Proposed Maintenance Concept Using a Data Link
`
`information to resolve ambiguities and isolate
`faults to t he SRA level . By using this approach ,
`diagnosing failures should be more effective than
`the classica l approach of trying to reproduce the
`maintenance problem in a •shop environment.• Once
`the faulty SRA is identified, the system locates a
`replacement in the supply system.
`Immediate action
`is taken to have the part d~spatched to the base
`where the f l ight will terminate so that the faulty
`SRA can be r eplaced and the avionics restored to
`fu l l operati onal capability. The current alterna(cid:173)
`tive to this approach is to wait until the aircraft
`has returned to base and is turned over to mainte(cid:173)
`nance personnel.
`
`Although the time advantage in transmitting fault
`information over a data link may not seem
`significant for a short mission, the additional
`lead time until maintenance personnel are
`actually diagnosing faults can result in a
`significant delay.
`In an environment in which
`rapid turnar ound of aircraft to maintain a high.
`sortie rate is important, the use of a data link
`to provide the maintenance facility with fault
`data in real time becomes very significant.
`
`In addition to transmitting avionics fault mes(cid:173)
`sages over a data link , engine-monitoring mes(cid:173)
`sages would similarly be transmitted using the
`same facilities. The main difference in the
`engine data would be the actions required by the
`ground maint enance system. Engine-monitoring
`data do not necessarilY indica~e an existing fault
`condition and, as such, urgency of maintenance
`action is not the issue; rather , the issue is
`scheduling preventive maintenance in an efficient
`manner to optimize maintenance resources and mini(cid:173)
`mize the unavailability of the aircraft .
`
`Data Link Requirements
`
`As mentioned previously, the volume of mainte(cid:173)
`nance data t hat would be transmitted by each
`aircraft for status reporting of fault information
`
`is minimal. The volume of data for engine(cid:173)
`monitoring messages would be somewhat greater but
`would still be considered a minimal demand on the
`data link system. This is presuming t hat t he
`frequency of transmission of the engine-monitoring
`data is comparable to that empl oyed over the. air(cid:173)
`line ACARS (between 5- and JO-minute intervals).
`The data requirements for the system would mainly
`be determined by the number of aircraft using the
`system in a given area . Assuming a maximum of 50
`aircraft using a single 3 KHz channel with a
`digital modem similar to ACARS, there should be
`adequate capacity.
`
`An alternative to using a voice channel would be
`to establish a series of maintenance messages
`that could be transmitted over planned data links
`such as the Joint Tactical Information Distribu(cid:173)
`tion System (JTIDS). This alternative would only
`accommodate aircraft equipped with JTIDS, which,
`in the case of the Air Force, may be a small per(cid:173)
`centage of the aircraf~ inventory. Similarly, the
`Navy will not have a JTIDS data link capability on
`many aircraft that will be operational in the
`1990s. Although the data link capacity available
`through JTIDS would accommodate low-priority
`maintenance messages, the software changes needed
`to process additional messages could pre~ent
`problems at this stage in the development. For
`these reasons a UHF voice channel with a digital
`modem, similar to the ACARS digital modem, would
`appear to be the preferred approach. The ground
`communications system to interconnect operators
`with maintenance and supply facilities would use
`existing digital transmission facilities such as
`the Defense Digital Network (DON).
`
`Advantages of Remote Maintenance Using a Data Link
`
`The concept of using a data link to transmit
`maintenance data to military ground f~cilities
`could have the _following significant advantages:
`
`Avionics faults would be identified to an
`LRU and to the extent possible, to an SRU,
`
`506
`
`BOEING
`Ex. 1013
`
`

`
`during a mission. Replacement of faulty LRUs
`and SRUs could be accomplished on the flight
`line immediately upon return from mission,
`with the aircraft returned to complete opera(cid:173)
`tional status in minutes rather than hours or
`days.
`
`Those faults . which cannot be unambiguously
`identified to LRU/SRU could be further diag(cid:173)
`nosed by using an expert system, Additional
`information would be requested by the expert
`system from the ~ircraft mission computer
`concerning the failure . The response would
`be used to make a diagnosis.
`
`Inte rmit t ent faults could be diagnosed in
`actual operating conditions rather than being
`subjected to extensive bench testing to repro(cid:173)
`duce the fault .
`
`A centralized ground maintenance facility
`with an expert system would reduce some of
`the specialized personnel and equipment
`requirements of intermediate-level facili(cid:173)
`ties . This would reduce the size and com(cid:173)
`plexity of the AIS/AIMD organization, thereby
`prov iding better mobility and decreased oper(cid:173)
`ating cost.
`
`Problems
`
`Implement ation of the concepts addressed herein
`will pres ent some problems that must be recog(cid:173)
`nized. ~ hese problem areas are as follows:
`
`The effective implementation of avionics
`fau l t monitoring depends on an effective
`int egrated BIT. Although new aircraft will
`be employing BIT, the capability would not be
`available on existing operational aircraft.
`Cons equently, the implementation of mainte(cid:173)
`nance monitoring using a data link would
`ini t ially be limited to new aircraft. As
`older aircraft undergo major upgrades of avi(cid:173)
`onic s or are replaced, they could adopt the
`data link maintenance concept .
`
`on-condition monitoring of engine performance
`is not receiving complete acceptance within
`the military as a replacement for scheduled
`maintenance for reasons addressed earlier.
`The value of using a data link to transmit
`eng i ne-monitoring data versus recording the
`data is of questionable benefit if maintenance
`scheduling action is not taken upon receipt
`of the data .
`
`The ground maintenance system needed to sup(cid:173)
`port this proposed maintenance concept would
`need to integrate operations, maintenance,
`and supply into a common data link system.
`Current l y, these are considered separate
`functional areas with supporting communica(cid:173)
`tions systems uniq~e to the requirements of
`each area .
`
`Currently, a data link capability from
`aircraft to ground sites is not universally
`available. Aircraft operating in tactical
`data systems nets have this capability at
`the present time, but many aircraft rely on
`voice nets for air-to-ground communications.
`The addition of a data modem to provide data
`link capability over existing UHF voice
`channels would require the use of additional
`avionics equipment that could present weight
`and space problems.
`
`Aircraft processor capability is often a
`limitation in aircraft improvements.
`Planning for remote maintenance monitoring
`should include provision for increasing
`processing capability in the development of
`a new aircraft or in major upgrade programs.
`
`·
`
`summary
`
`The trend toward digital avionics in new aircraft
`emphasizing extensive use of BIT suggests changes
`in the traditional approaches to maintenance. A
`maintenance concept is proposed that would employ
`data links to permit the remote monitoring of
`maintenance data . Advance notice of faults in
`avionics equipment and degraded performance of
`engines could be used to more efficiently sched(cid:173)
`ule maintenance actions, including the location
`and prepositioning of replacement parts. An
`improvement in operational readiness would result .
`Some problems are expected in implementing this
`approach in the near term, but pl anning should
`begin now for an evolutionary implementation in
`the 1990s.
`
`References
`
`(1) u.s. Air Force Technical Order lC-SA-2-G,
`"Instruments, C-5A Aircraft," 13 February
`1984, Kelly Air Force Base, Texas.
`
`{2) Presentation to 20th Joint Propulsion Con(cid:173)
`ference , AIAA/SAB/ASME, " Evaluation of
`Benefits of the A-10/TF34 Turbine Engine
`Monitoring System Squadron Integration
`Program," AIAA-84-1414, June 11-13, 1984 ,
`Cincinnati, Ohio.
`
`(3) Presentation to 17th Joint Propulsion
`Conference, AIAA/SAB/ASME , "A-10/TF34
`Turbine Engine Monitoring system -
`Evaluation and Implementation ,• AIAA-81-
`1447, July 27-29, 1981, Colorado Springs,
`Colorado .
`
`(4)
`
`"Avionics Fault Tree Analyzer, • Michael E.
`Harris, AGARD* Proceedings i343 , Paper
`120, 18-23 April 1983.
`
`*AGARD is the Advisory Group for Aerospace
`Research and Development.
`
`. :
`
`507
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`BOEING
`Ex. 1013