AVIONICS SYSTEM MAINTAINANCE

ELECTRICALSatisfactory performance of an aircraft depends up on the continued reliability of

electrical system. Reliability is proportional to amount of maintenance received and knowledge of men who performed such maintenance.

Maintenance:

The performance of tasks required to ensure the continuing airworthiness of an aircraft including anyone or combination of overhaul, inspection, replacement, defect, rectification and the embodiment of a modification or repair.

Progressive Inspection:

An inspection that may be used in place of an annual or 100 Hrs inspection. It has same scope as an annual inspection. But it may be performed in increments soothe a/c will not have to be out of service for a lengthy period of time.”This inspection is used for light A/c”.

Down Time:

Any time during which an A/C is out of commission and unable to be operated.

Continuous airworthiness inspection programme:

An inspection programme that is a part of contiguous airworthiness maintenance programme approved by FAA for certain large A/C including turbine powered rotorcraft.

Modern A/c has complex system. A high degree of knowledge and skill is needed to identify the problems so that down time is reduced.

Remove and replace or Rand R maintenance is the only way flight schedules can be maintained today. This type of maintenance requires a good knowledge of systematic trouble shooting so that only the offending component is changed.

Troubleshooting:

It is a procedure used in A/c maintenance in which the operation of malfunctioning system is analyzed to find the reason for malfunction and to find a method for returning the system to its condition of normal operation.

Blackbox:

It is a term used for any portion of an electrical or electronic system that can be removed as a unit. A black box does not to be a physical box.

Circuit diagrams, wiring diagrams, routing charts (location charts) and troubleshooting tools like continuity light, multimeter and clampon ammeter are helpful for troubleshooting .modern A/C deployed with BITE (built in test equipment)systems.

Rules for systematic trouble shooting:

1. Know the way the system should operate .it is the secret of successful troubleshooting .the way a component works, correct voltage and current at a specified test points and correct frequency and waveform of an alternating current at these test points must be known.

2. Observe the way the system is working/operating. Any difference between the way system is operating and they it should operate is an identification of trouble. Current or voltage is too low or too high or components that show signs of overheating are indications that a system is not operating correctly.

3. Divide the system to find the trouble, time is valuable. When the system is not operating is not operating as it should we must find whether the trouble is in the beginning of the system or hear its end. To do this open the system near its middle and check the conditions there .everything is ok the trouble is between there to end and vice versa.

4. Look for the obvious problem first and make all measurements at the points where they are easiest to make .popped out circuit breakers, blown out fuses and corroded ground connections are usually easy to check and are the cause of many electrical system malfunction.

There are usually there types of diagrams produced for A/C .the ATA-100 system has a much greater application internationally.

Circuit Diagrams:

Theoretical nature show the internal circuit arrangements of electrical and electronic components both individually and collectively as a complete distribution or power consumer system in the detail necessary to understand the operating principle of the components and system.

Circuit’s diagrams are normally drawn in the “aircraft on the ground condition with main power supply off .In general switches are in off”. Position and all components such as relays and contactors are in de “energized (demagnetize)”state. Circuit breakers are closed.

In the event it is necessary to deviate from these standard condition a note is added to the diagram to clearly define the condition selected.

Wiring diagrams:

More practical in nature. They show how all components and cables of each individual system making up the whole installation are to be connected to each other .Their locations within the A/C and the groups of groups of figures and letters to indicate how all components can be identified directly on the A/C.

Routing Charts:

These charts have similar functions to wiring diagrams, but are set out in such a manner that components and cables are drawn under “location” heading so that the route of distribution can be readily traced out on the A/C. In some cases both functions may be combined in one diagram.

Wiring diagrams and routing charts are use full for maintenance engineers to assist them in their practical tasks of testing circuits fault finding and installation procedures.

The number of diagrams or charts required depends upon size of A/C and its electrical installations .it can vary from few pages at the end of maintenance manual small light A/C (Cessna) to several massive volumes for large transport A/C.

Cable Identification

Air transport association of America under specification

Positon1: unit number. It is used where component have identical circuits Eg: components of a twin generator system. This number is omitted where cables are used singly.

Position2: circuit function. It designates the circuit or system with which cable is connected. The second letter indicates to further sub system.

Position3: wire number. It is used to differentiate between cables which don’t have common terminal in the same circuit. Starting from the busbar with lowest number.

Position4: segment letter. Signifies the segment of cable (the portion of the cable between two terminals or connections). It starts from letter “A” from power source goes on with alphabetical sequence (excluding letters I and O). Different letter is used where cable segments have common terminal or connection.

Position5: wire size in number as per American wire gauge (Awg). No number for coaxial cable. Thermo couple cable – (dash)

Position6: letter indicates whether a cable is used as a connection or each point. ‘N’ indicates earth connected ‘V’ supply in single phase. A, B, C three phase circuits. No letter for DC

Thermocouple cables by type of conductor material

Al alumel, Ch chromel, Cu copper, Cn constantan.

The coding schemes adopted for items of electrical equipment, control panels connector groups. Junction boxes etc are related to physical locations within the aircraft and for the purpose aircraft are divided in electrical zones. A reference letter and number are allotted to each zone and also to equipment connectors. Panels etc so that they can be identified with in the zones. The reference letters and numbers are given in appropriate wiring diagram and are correlated t the diagrammatic representation of all items. In the aircraft itself reference are marked on or near the related items.

Common electrical faults

Open circuit: a circuit with an unwanted disconnection or infinite resistance. Like Broken wires, defective connectors. Loose terminals or any other which creates circuit disconnection.

Short circuit: a circuit with an extra. Unwanted connection

Two types short to ground form when + wire touches –ve ground (extremely low resistance infinite current flow) accidently.

A cross short takes place when two or more circuits are connected accidentally together.

Short circuits are due to friction between two wires or between a wire and the air frame.

Trouble shooting tools:

Continuity light (tester):

Bug light (3 volt bulb) or continuity tester used to trace wires in the system. Locate shorts and open circuits and to determine whether a fuse is good or bad.

When using a continuity tester “an electrical power must be OFF” to the circuit. Connect the black test lead to one end of the circuit and green lead to other end. The bulb will light up if there is continuity. In case of disconnection bulb does not glow.

Note: never cut or pierce insulation of aircraft cable to check the continuity. Check only at the correct points studs, connectors, junction boxes etc.

The “Hot light” is to check the presence of voltage at various points. In this case aircraft supply must be “ON” appropriate switches and circuits breakers must be ON. Black lead is to be connected to some ground point on the aircraft structure. Touch the red lead of the got light to the point where you want to check for voltage. The light will come on if there is voltage. No light in case of no voltage.

Multimeter:

An electrical test instrument that consists of a single current measuring meter and all of the needed components to allow the meter to be used to measure voltage, resistance, current.

Multimeter may be an analog or digital type displays.

In digital multimeter the indication is in the form of liquid crystal display in discrete numbers.

Clamp on Ammeter:

An electrical instrument used to measure higher current without opening the circuit through which it is flowing.

Used for trouble shooting hydraulic and fuel, Battery charging system.

Oscilloscope:

They have a small screen of 3 inch diagonal which is easy to carry to the aircraft. Used to display on CRT. The wave form and frequency of the voltage being measured.

Modern electronic systems have mode dual trace oscilloscope. By which you can look at the signals on the input and output of a circuit at the same time.

Inspections:

A suggested list of items to look for and checks to be performed are

a. Damaged or over heated equipment, connections, wiring and installation.b. Excessive resistance at high current carrying connections as determined by milli-volt

drop test.c. Misalignment of electrically driven equipmentd. Poor electrical bonding.e. Dirty equipment and connections.f. Improper support of wiring and conduit.g. Loose connections, terminals, and ferrules.h. Continuity of fuses.i. Condition of electric lamps.j. Insufficient clearance or poor insulation of exposed terminals.k. Broken or missing safety wire, cotter pins, etc.I. Operational check of electrically operated equipment such as motors, inverters, generators,

batteries, lights, etc.m. Voltage check of electrical system with portable precision voltmeter.n. Miscellaneous irregularities such as poorly soldered or loose swaged terminals, loose

quick disconnects, broken wire bundle lacing, broken or inadequate clamps, and insufficient clearance between exposed current-carrying parts and ground.

Cleaning And Preservation Frequent cleaning of electrical equipment to remove dust, dirt, and grime is

recommended. Fine emery cloth may be used to clean terminals and mating surfaces if they are corroded or dirty. Crocus cloth or very fine sandpaper may be used to polish commutators or slip rings. Do not use emery cloth on commutators since particles from the cloth may cause shorting and burning.

Adjustment. Accomplish adjustments to items of equipment such as regulators, generators, contactors,

control devices, inverters, and relays outside the airplane on a test stand or test bench where all necessary instruments and test equipment are at hand. Follow the adjustment procedures outlined by the equipment manufacturer.

Insulation of electrical equipment.In some cases, a unit of electrical equipment is connected into a heavy current circuit,

perhaps as a control device or relay. Such equipment is normally insulated from the mounting structure, since grounding the frame of the equipment may result in a serious ground fault in the event of equipment internal failure. If a ground connection for a control coil must be provided, use a separate small gauge wire.

Bus bar maintenance. Periodically check bus bars used in aircraft electrical systems for general condition and

cleanliness. Grease, oxide, or dirt on any electrical junction may cause the connectors to overheat and eventually fail. Clean bus bars by wiping with a clean soft cloth saturated with Stoddard solvent and drying with a clean soft cloth.

Junction boxes.a. Junction Box Construction. Fabricate replacement junction boxes using the same material

as the original or from a fire-resistant, nonabsorbent material, such as aluminum alloy or an acceptable plastic material. Where fire-proofing is necessary, a stainless steel junction box is recommended. Rigid construction will prevent "oil-canning" of the box sides, which could result in internal short circuits, ^n all cases, provide drain holes in the lowest portion of the box.

b. Internal Arrangement. The junction box arrangement should permit easy access to all in-stalled items of equipment, terminals, and wires. Where marginal clearances are unavoid-able, insert an insulating material between current-carrying parts and any grounded sur-face. It is not good practice to mount equipment on the covers or doors of junction boxes, since inspection for internal clearance is impossible when the door or cover is in the closed position.

c. Junction Box Installation. Securely mount junction boxes to the aircraft structure in such a manner that the contents are readily accessible for inspection. When possible, face the open side downward or at an angle so that loose metallic objects, such as washers or nuts, will tend to fall out of the junction box rather than wedge between terminals.

d. Junction Box Wiring. Junction box layouts must take into consideration the necessity for adequate wiring space and possible future additions. Lace or clamp electric wire bundles inside the box in a manner that terminals are not hidden, relay armatures are not fouled, and motion relative to any equipment is prevented. Protect cable at entrance openings against chafing using grommets or other suitable means.

POWER SOURCES AND DISTRIBUTION SYSTEMS

Battery electrolyte corrosion. Electrolyte spilled during ground servicing should be neutralized at once with solutions

of sodium bicarbonate (for acid electrolyte) or boric acid, vinegar, or a 3 percent solution of acetic acid (for alkaline electrolyte). Residue should be washed off with clean water and the area thoroughly dried.

Generators and Alternators. Inspect generators and alternators and their associated wiring and distribution systems

for wear, damage, general condition, and proper functioning to assure the continued satisfactory operation of the electrical system. Frequent visual inspections, operating checks of all electrical circuits and equipment, and replacement or repair when deficiencies are found are effective in minimizing electrical troubles and hazards in aircraft.

Alternator diodes. Alternators employ diodes for the purpose of converting the alternating current to

direct current. These diodes are electronic devices and are particularly susceptible to damage if abused. A diode will allow passage of current in one direction with little resistance, but will allow passage of current in the opposite direction only if the voltage applied exceeds that value for which the device was designed. A voltage surge in the line, if it exceeds the design value, will destroy the diode very quickly.

Diode protection.The best protection against diode destruction by voltage surges is to make certain that

the battery is never disconnected for the aircraft electrical system when the alternator is in operation. The battery acts as a large capacitor and tends to damp out voltage surges. Make certain that the battery is never connected with reversed polarity. This will subject the diodes to a direct short circuit and will generally destroy them instantly.

Alternator/battery connections. Some alternators require that the battery be connected in the circuit initially before it

will produce any output.

Static electrical power converters.Static power converters employ solid state devices to convert the aircraft primary electrical source voltage to higher values for the operation of radio and electronic equipment. They contain no moving parts and are relatively maintenance free. Various types are available for AC

to DC or DC to AC conversion. Exercise care in locating and mounting static converters to insure adequate ventilation for cooling purposes. Heat radiating fins should be kept clean of dirt and other foreign matter which may impair their cooling properties.

Cleaning and Preservation. Frequent cleaning of electrical and electronic equipment to remove dust, dirt, and

grime is recommended. Fine emery cloth may be used to clean terminals and mating surfaces if they appear corroded or dirty. Crocus cloth or very fine sandpaper should be used to polish commutators or slip rings. Use of emery cloth on commutators is not acceptable because metallic particles from the cloth may cause shorting and burning.

Miscellaneous check items.

Make frequent checks for miscellaneous irregularities such as loose terminal connections, poorly soldered or loosely swaged terminals, missing safety wire, loose quick-disconnects, broken wire bundle lacing, broken or inadequate wire clamps, and insufficient clearance between exposed current-carrying parts and ground. Replacement or repair should be accomplished as a part of routine maintenance.

Adjustment and repair. Accomplish all adjustment, repair, overhaul, and testing of electrical equipment and

systems in accordance with the recommendations and procedures set forth in the aircraft and equipment manufacturers.

Electrical switch inspection. Special attention should be given to electrical circuit switches, especially the spring-

loaded type, during the course of normal airworthiness inspection. An internal failure in this type of switch may allow the switch to remain closed even though the toggle or button relurns to the "off position. During inspection, attention should also be given to the possibility that improper switch substitution may have been made.

NOISE SUPPRESSION

General. Elimination or suppression of sources of radio interference within the aircraft is

necessary in order to obtain the optimum performance of airborne radio equipment. This is done by bonding, shielding, and the use of static dischargers.

Bonding. Radio equipment should be bonded to the aircraft in order to provide a low impedance

ground and to minimize radio interference from static electricity charges. Bonding jumpers should be as short as practicable and be installed in such a manner that the resistance of each connection does not exceed 0.003 ohm. Where a jumper is for radio-noise prevention only and not for current-carrying purposes, a resistance of 0.01 ohm is satisfactory.

Shielding. The most effective method of minimizing engine ignition radio interference is to shield

the ignition system. Use a metallic braid covering and special end connectors for ignition wires between the magneto and spark plugs. The primary leads to the magneto and the magneto switch itself should be shielded. Provide shielded type spark plugs and a shielded metal cover for the magneto if it is not so equipped. All connections in the shielding should be tight metal-to-metal contact.

Spark plugs. The engine ignition noise may be suppressed by replacing the spark plugs with resistor

spark plugs of a type approved for the engine if it is not feasible to shield the engine ignition system.

Filters. If an intolerable radio noise level is present despite shielding of the ignition wiring and

plugs, it may be necessary to provide a filter between the magneto and magneto switch to reduce the noise. This may consist of a sin, ffle by-pass capacitor or a combination of capacitors and choke coils. When this is. done, theshielding between the filter and magneto switch can usually be eliminated and the special shielded magneto switch need not be used.Inspect supporting brackets and wiring details for magneto filters for conformance with stand-ard aircraft electrical practice. The reliability of the magneto filter installation should be at least equivalent to that of the remainder of the magneto ground lead installation.

Precipitation static. Precipitation static is a general term applied to noise in radio receiving systems caused

by precipitation. It is not always caused by true precipitation, such as ice, snow, or rain. Dust, sand, or other airborne particles may cause it. It may be the result of ionization in the exhaust of jet engines. As a result of precipitation static charging, the electrical potential of the aircraft rises until it reaches the corona threshold. Corona is the discharge of electric current from an object into the surrounding air and occurs as short pulses of current and produces a noise spec-

trum which contains appreciable energy at radio frequencies. The noise produced is coupled into the aircraft antennas.

Static dischargers. Static dischargers are installed on aircraft to bleed off precipitation static before the

potential reaches the corona threshold. These dischargers are normally mounted on the control surfaces and other extremities of the aircraft.

The three major types in use are: (1) Flexible, vinyl-covered, carbon-impregnated braid, (2) Semi flexible metallic braid, and(3) Null-field.

Maintenance of static dischargers.Inspect flexible and semi flexible dischargers for physical security of mounting

attachments, wear or abrasion of wicks, missing wicks, etc. Inspect flexible, vinyl-covered wicks to assure that one inch of the inner braid extends beyond the vinyl covering. Null-field discharges are epoxy bonded to the aircraft structure. Measure the resistance of the bond to determine compliance with the manufacture’s recommended tolerances, and inspect for physical damage.

Battery installation.

Cables/Connectors. Use cables and/or connectors that are adequately rated for the current demand and are

properly installed (See AC 43.13-1 A, "Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair," chapter 11). It may be necessary to contact the battery manufacturer to determine current value of the battery at the 5-minute discharge rate. Cable size can also be selected by using the same gage as used on a previously approved production aircraft with the same battery.

(1) The cables should be of sufficient length to prevent undue strain on the battery connector or terminals.

(2) Clamp and protect cables, including the bus, in a very secure manner. Since these units are not fused, any fault could cause loss of the entire electrical system in addition to a possible

(3) Route, cables so that cable or terminals cannot short, to the battery case or hold-down

(4) Route cables outside the battery box whenever practicable to prevent corrosion by acid fumes. When internal routing is unavoidable, protect the cable inside the box with acid-proof tubing. Assure that cables will not be inadvertently reversed on the battery terminals either by proper cable lengths and clamps or, if this is not practicable, use conspicuous color coding.

Battery Cutoff. Install a battery cutoff relay to provide a means of isolating the battery from the

aircraft's electrical system. An acceptable battery cutoff circuit is shown in figure 10.6. Mount the relay so that the cable connecting the relay to the battery is as short as feasible, in any case not to exceed two feet, to reduce the possibility of a fire occurring because of a short within this section of cable.

In the constant voltage charging system the maximum permissible voltage for lead acidbattery is 2.35V per cell for Ni-Cd 1.42-1.5V per cell.

The KOH will freeze at approximately -75F or -59C.

The serviceability state of the Ni-Cd battery can be checked by measured discharge.

Digital a/c electrical system: They provide for greater reliability faster response, smaller equipment light equipment, and

lower operating cost compare to analog system. It is no wonder modern commercial A/c contains counters digital system & ccts. Digital system increases the mean time.

AHRS – A/c heading & reference system (working on optic fiber infer metric) between the failure &

reduce the subsequent repairs time of failure components. The BITE equipment provides rapid fault isolation detection. The majority of the digital system A/c contain a lot of 'LRU' Defective LRU's can be identified quickly by the BITE & replaced during ground maintenance use of the LRU's & BITE concepts greatly reduces A/c maintenance. Another concept of digital A/c technology is to remove as many moving parts from electrical system as possible For E.g. S/W's are replaced with proximity sensors. Relays are replaced with transistor & instruments are replaced with digital displays. In the flight compartment the CRT displays replace conventional analog instruments. Thus eliminates of moving parts. A CRT display located in instrument panel employ highly efficient & multi band pass optical filters. In order to achieve enough contrast brightness & resolution to make them sun light readable.

Trouble shooting digital ccts.The trouble shooting is normally done by the logic trouble shooting techniques which can be

applied to both analog & digital systems well as for hydraulic, pneumatic & other systems also. Logic trouble shooting is nothing but a sequence employing a flow chart of logical faults repair for an electrical system. The flow chart typical of trouble shooting avionics system. The system asks 'yes' or 'no' system & directs the technician to the correct means of repair. The increased use of LRU's has made the trouble shooting method very feasible.

BITE: Bite systems are designed to provide fault detection fault isolation & operational verification

after the defect repair. Each fault detection is performed continuously during the system operation. If a defect is sensed the BITE initiates an appropriate control signals to isolate the defect component. For repairing the defective system the line engineer can utilize the byte to identify the byte to identify the fault. After the repair the system should be run through again for operational check. The BITE will again monitor the system & confirm the repair.

A-typical commercial transport A/c. contains several BITE systems. Eg. B-757 or B-767 A/c have BITE systems to monitor the electric power environmental control auxiliary power & flight control system ,7 separate BITE units are located in the electronic equipment for this purpose- Each of the BITE boxes receives simple i/p' s from several individual components of the systems concerned. The BITE systems are relatively "simple & each system are contained within an LRU. (line replaceable unit).

A BITE system performs two types of test programs1. Operation2. Maintenance testThe operational programme is designed to check i/p signals, protection circuitry, control circuitry, o/p

signals & the operation of BITE circuitry.

The maintenance programme of BITE is recorded into the system only when the A/c is on the ground & maintenance test routine is required. When requested the maintenance BITE exercise all i/p circuitry & software routines of the system being checked. The o/p data are then monitored & faults are displayed on the bite.

IACS: Integrated Avionic Computer System

DAV: Data Acquisition Unit

BPCU: Bus Protection Control Unit.

ACARS - Arnic Communication Addressing & Reporting system

EIU: Electronic Interface units

IAC: Integrated Avionics Computer

Trouble Shooting with BITE:BITE systems provide fault detection continuously during A/c operation. If a fault is

Detected the BITE system stores the necessary defect information in a nonvolatile, Memory & sense the appropriate display signal to the flight deck.

If the fault requires immediate attention, the flight crew will notify ground engineer via the radio Transmission. The technician must access the appropriate BITE system on ground for the

Fault isolation. The BITE system will display the failure data with code information. A Typical simple system of BITE incorporates. Go or NOGO red or green light on the Equipment black box or LRU.

But in the advanced system have a means to terminals Data from the A/c to the maintenance facility on ground during the flight. This type of Means is known as ACARS. The BITE system shown in fig (a) is incorporated with BPCU (Bus Power Control Unit) which monitors the entire electrical power ccts. When BITE button is depressed a 24 character faults display system is activated. This display fault information in a coded message which is decoded by referring maintenance manual Note that the fault information

on the system is displayed only for 2 sec. The Display automatically advances to the next fault. After system fault is rectified the Button should be pressed to reset & their operational check to be performed.

Multipurpose control display unit: MCDU- is used to access a more advanced BITE system. In some A/c the access is from the

electronic equipment bay. In some A/c the access is through the controller located in the flight deck on the instrument

panel. The display information is obtained from the EICAS. The MCDU system normally employed in B-747 it receives the digital data in an ARINC -

429 format from the thrust management the flight control, FMS along with the EICAS i/p's. The MCDC also monitors both the flight faults and perform a ground test function also.

A flight desk effect means any EICAS display or a discreet annunciator used to inform the pilot of an in flight fault.

When' the A/c lands the MCDU automatically records any in flight fault from the last in a nonvolatile memory.

To access the memory engineer must cycle the MCDU ON & OFF again. This will result in a test of -MCDU. After the internal test has been completed & 'OK' ed by the display the technician should select the in flight mode of operation. The unit will respond accordingly with all the faults listed in order of occurrence.

At the end of the fault data the unit will ask if you want from previous flights. The MCDU stores for a maximum of ten flights.

In case of MCDU located in equipment bay fault data appears on LED' display as explained earlier. On this type of MCDU the top line display the flight on which the fault occurred & the related flight deck information. The bottom line displays a faulty LRU to be replaced. In case of MCDC access from the flight deck the messages are displayed on the EICAS unit.

CMC System: (Central Maintenance Computer):-The latest BITE equipment is known as CMC. This system is designed to perform in flight &

ground test of Very a/c system, which can be accessed from a centrally located control display unit. The CDU is located on the central console in the cockpit. This system is found in B-747-400. The CDU is a CRT display. A CMC printer is incorporated to write the reports of the flight data. A software data loader to down load the faults on a computer disk. If ACARS is Installed flights faults can be transmitted to the ground facility & also will be able to answer all maintenance data from the ground facility.

There are two CMC’S fitted in the A/c. the CMC receive up to 50 digital ARINC -data i/p's & various discreet i/p's. Each CMC has 10 ARINC o/p's. One is a cross talk bus to the other CMC. The o/p' s are send to A/c systems to the left CMC.if only one CMC is available it must be installed in the left slot.During flight the CMC receive the fault data from the A/c's EIU (Electronic Interface Units) & other digital discreet signals record a in flight failure. The EIU's monitor all system parameters & control the displays of all EICAS & EFIS system.

Once the A/c is on ground the CMC'S can be interrogated for any history of in flight faults stored in a non volatile memory, up to 500 faults can be stored in the memory.

The first page of CDU shown above is used for maintenance & operations. The second page for in-depth trouble shooting. A function is selected from the menu by pressing the button adjacent to it. There are three types of faults.

1. Existing faults2. Present leg faults3. Fault history (faults recorded during present leg or previous flight).

Depressing the button for the ground test tells the CMC to test the LRU's the EICAS maintenance page will activate the read time display of various systems & also will allow you to access to other maintenance pages.

The confidence check allows the technician to perform test required before a flight.

CFDS: Centralized fault display system in AirbusAn airbus~A-320 employs a similar system 'like CMC called as CFDS. This system

classified the defects into three categories.

Class 1 faults: The faults which have got operational consequence on the flight. The crew is notified either by an amber or red warning on the ECAM system or by discreet. Instrument flags. The pilot must report class1failure in his log book since they require immediate attention & action before next flight.Class 2 defects: are displayed to the pilot by means of ECAM system only after landing & Engine shut down. Class2 defects must be reported by the pilot in the log book because they cannot be left unattended until the next maintenance. The class 2 faults are normally categorized by the MEL.Class 3 failures: are not reported by the pilot & can be left unattended until next scheduled maintenance. They are displayed only during access of CFDS data.

Logic flow charts:

A type of graphic charts that can made up for a specific process or procedure to help follow the process or procedure through all of its logical steps in maintenance.

Logic flow charts for trouble shooting. An oval is used to show the beginning and the end of the problem. A diamond is used when there is a decision to be made. The instructions in the rectangle tell what to do next.