Aircraft Electrical and Avionics System Overview
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Questions and Answers

What type of lamps are used in passenger cabins?

  • Halogen lamps
  • Fluorescent lamps
  • Both A and B (correct)
  • None of the above

    • What is the purpose of the CIDS system in Airbus aircraft?

    To provide control for the cabin system, including audio, interphone system, and lights.

    What is the purpose of the ACESS system in Boeing aircraft?

    To provide control for the cabin system, including audio, interphone system, and lights.

    What is the purpose of the FAP in the CIDS system?

    <p>To provide indication and control to the cabin systems.</p> Signup and view all the answers

    What is the purpose of the DEUs in the CIDS system?

    <p>To act as an interface for the directors and the output devices.</p> Signup and view all the answers

    What is the purpose of the passenger signs in aircraft?

    <p>To indicate messages of 'no smoking' and 'fasten belts' or 'return to seat'.</p> Signup and view all the answers

    What should be used to soak up electrolyte spillage on metal?

    <p>Sawdust or similar</p> Signup and view all the answers

    What should be done to neutralize an acid spillage on fabric?

    <p>Dab with ammonia</p> Signup and view all the answers

    What is the purpose of the call system in aircraft?

    <p>To alert the cabin crew to passenger needs.</p> Signup and view all the answers

    What is the primary consideration for designing a lighting system in a passenger cabin?

    <p>Appealing and efficient lighting with minimal weight penalty</p> Signup and view all the answers

    DC generators are self-excited and independent of other supplies.

    <p>True</p> Signup and view all the answers

    What is the power supply for general illumination in an aircraft?

    <p>Both A and B</p> Signup and view all the answers

    What is the purpose of the standby and emergency lights in aircraft?

    <p>To provide lighting in the event of a power failure.</p> Signup and view all the answers

    In a conventional alternator, rotating magnets induce a stator output, which is then rectified and regulated to _.

    <p>DC</p> Signup and view all the answers

    What is the purpose of the main battery in aircraft?

    <p>To provide power to important systems and circuits in the event of a generator failure.</p> Signup and view all the answers

    What is the purpose of navigation lights on an aircraft?

    <p>To provide high intensity light for identification of airplane position and orientation</p> Signup and view all the answers

    What is the purpose of anti-collision lights?

    <p>All of the above</p> Signup and view all the answers

    Match the following components with their function in an electrical generation system:

    <p>Voltage Regulator = Supplies and controls the generator field Load Controller = Synchronizes generator outputs by trimming CSD governors GCR (Field Relay) = Trips when a fault occurs in the generator or its components GB (Generator Breaker) = Connects and disconnects generator output to its bus</p> Signup and view all the answers

    What is the difference between primary and secondary cells?

    <p>Primary cells cannot be recharged, while secondary cells can be recharged.</p> Signup and view all the answers

    What is the purpose of the nickel-cadmium battery charger?

    <p>To regulate the charging current to prevent overcharging and thermal runaway.</p> Signup and view all the answers

    What is the purpose of strobe lights?

    <p>To provide an anti-collision warning in flight</p> Signup and view all the answers

    Direct and proximate exposure to strobe light flashes can cause permanent eye damage

    <p>True</p> Signup and view all the answers

    What is thermal runaway?

    <p>A condition where a heavy charge current causes a battery to overheat, leading to further resistance reduction and increased heat generation.</p> Signup and view all the answers

    What is the purpose of landing lights?

    <p>To illuminate the landing area during takeoff and landing</p> Signup and view all the answers

    What is the purpose of ice inspection lights?

    <p>To illuminate the wing leading edges and engine nacelles for visual inspection</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>AOA sensor = Measures angle of attack directly with vane or probe Stick-shaker system = Simulates natural buffeting caused by a stalled condition ADIRU = Calculates air data parameters for various aircraft systems</p> Signup and view all the answers

    What is the purpose of internal lights in the flight deck?

    <p>To provide general illumination and instrument lighting</p> Signup and view all the answers

    What are some functions of the control and protection unit mentioned in the text?

    <p>Synchronizing (paralleling) control and/or protection</p> Signup and view all the answers

    What can lead to automatic tripping of the breakers according to the text?

    <p>All of the above</p> Signup and view all the answers

    Nuisance trip protection is necessary when the engine is shut down after a flight.

    <p>True</p> Signup and view all the answers

    A __ protects against AC system distribution faults by monitoring current diversion within its zone.

    <p>differential protection</p> Signup and view all the answers

    Match the following emergency power generation components with their descriptions:

    <p>Ram Air Turbine = Supplies 115 Volts three-phase emergency AC power when normal sources are not available Static Inverter = Transforms direct current into single-phase alternating current for emergency use Emergency Generator = Driven by hydraulic system to supply AC emergency bus bars and part of AC essential bus bars</p> Signup and view all the answers

    What is the vertical speed indicator also known as?

    <p>rate-of-climb (ROC) indicator</p> Signup and view all the answers

    What does the airspeed indicator show?

    <p>Speed relative to the air</p> Signup and view all the answers

    Total air temperature (TAT) is the static air temperature plus the rise in temperature due to the pitot effect.

    <p>True</p> Signup and view all the answers

    Total air temperature (TAT) probe needs some airflow through it to avoid heating of the measured air by the ________.

    <p>anti-icing heating element</p> Signup and view all the answers

    What is the purpose of compartment lights?

    <p>To illuminate cargo compartments, stabilizer access, and other areas</p> Signup and view all the answers

    How are the roles of rectifiers summarized?

    <p>Blocking and D.C. Supply</p> Signup and view all the answers

    Rectifiers allow one circuit to be isolated from another while serving common functions.

    <p>True</p> Signup and view all the answers

    What does TRU stand for in aircraft systems?

    <p>Transformer Rectifier Unit</p> Signup and view all the answers

    Current transformer secondary connections must be short-circuited when the primary is _____ if any part of their circuit is to be disturbed.

    <p>dead</p> Signup and view all the answers

    What is the purpose of the Pitot-Static system on an aircraft?

    <p>To sense pressure for speed and altitude</p> Signup and view all the answers

    What are the two important main properties exhibited by a gyro when the rotor is caused to spin at high speed?

    <p>Gyroscopic Inertia and Precession</p> Signup and view all the answers

    Define gyroscopic inertia.

    <p>Gyroscopic Inertia is the force of the gyro that opposes any other force that tends to change its plane of rotation in space.</p> Signup and view all the answers

    Precession occurs in the same direction as the applied force.

    <p>False</p> Signup and view all the answers

    The gyro horizon, or artificial horizon (AH), gives the _ and _ attitude of an aircraft relative to the vertical.

    Signup and view all the answers

    What is the principle of operation of the direct-reading compass?

    <p>Interaction of the earth's magnetic field with a suspended permanent magnet</p> Signup and view all the answers

    What are the common principal features shared by different types of compasses used in aircraft?

    <p>All of the above</p> Signup and view all the answers

    A newly installed compass does not require a compass swing.

    <p>False</p> Signup and view all the answers

    The angle between the true and magnetic meridian is called ________.

    <p>variation</p> Signup and view all the answers

    Match the following GPWS modes with their conditions:

    <p>Mode 1 = Excessive descent rate Mode 2 = Excessive closure rate with respect to rising terrain Mode 3 = Excessive altitude loss during climb-out without landing configuration Mode 4 = Insufficient terrain clearance without landing configuration Mode 5 = Excessive deviation below glide slope on front course approach Mode 6 = Altitude Callout Mode 7 = Windshear</p> Signup and view all the answers

    Define what gyroscopic inertia or rigidity refers to.

    <p>force of the gyro that opposes any other force that tends to change its plane of rotation in space</p> Signup and view all the answers

    What is precession in relation to a gyro?

    <p>angular displacement of plane of rotation of gyro when an external force is applied</p> Signup and view all the answers

    What are the two important main properties exhibited when a gyro is caused to spin at high speed?

    <p>Gyroscopic Inertia</p> Signup and view all the answers

    The gyro horizon instrument gives pitch and altitude indications of an aircraft.

    <p>False</p> Signup and view all the answers

    The gyro horizon uses a gyroscope with a spin axis that is kept __________ by a gravity-sensing device.

    <p>vertical</p> Signup and view all the answers

    Study Notes

    Electrical and Avionics

    Lights

    • Design considerations for lighting systems:
      • Passenger cabin: appealing, efficient, and minimal weight penalty
      • Flight deck: instrument reading ease under all natural light conditions
      • Warning lamps: not dimmed under all circumstances
    • Power supplies:
      • General illumination: 28V AC or lower
      • Standby lighting: 28V DC or lower (e.g. emergency lights battery)
      • Fluorescent lights: 115V/200V AC (normal AC generation)
    • Exterior lights:
      • Navigation lights: red (left), green (right), and white (tail)
      • Anti-collision lights: red flashing (beacon) and white strobe (high intensity)
      • Logo lights: illuminate airline emblem on vertical stabilizers

    Safety Precautions

    • Flash frequency: 40-100 cycles per minute
    • Avoid direct exposure to strobe light flashes
    • Handle quartz bulbs with care to avoid contamination
    • Wait 10 minutes after power removal before handling components

    Landing, Taxi, and Runway Turnoff Lights

    • Landing lights: mounted on wing leading edges
    • Taxi lights: sealed beam incandescent lamps (28V AC)
    • Runway turnoff lights: two sealed beam incandescent lamps (28V AC)

    Compartment and Internal Lights

    • Compartment lights: operate on 28V AC ground supplies with local switches
    • Flight deck lights:
      • Instrument panels: 115V white fluorescent tubes
      • Subdued general lighting: small dome and glare shield incandescent filaments (28V AC)
    • Passenger cabin lights:
      • Soft lighting: 28V incandescent filaments
      • Fluorescent tubes: cold cathode (200-500V)
    • Galley and toilet lights:
      • Halogen lamps (e.g. mirror light) and fluorescent lamps (tubes)
      • Connected to door locking mechanism for switching and/or dimming functions

    Lights Control

    • Centralized systems: e.g. CIDS (Cabin Intercommunication Data System) in Airbus
    • Components: directors, FAP (Flight Attendant Panel), DEUs (Decoder/Encoder Units)

    Passenger Signs

    • Indicate messages: "no smoking" and "fasten belts"/"return to seat"
    • Operated from the flight deck and supplied by a high priority bus

    Call Systems

    • Alert cabin crew to passenger needs
    • Activated from seats or toilets
    • Communication between cabin crew: handsets and call lights

    Standby and Emergency Lights

    • Automatically operate from the main aircraft battery in case of supply failure
    • Standby lights: either separate lamps or normal lamps switched to full brightness
    • Emergency lights: powered by centralized alkaline batteries or individual cells

    Electrical Power

    • Batteries: Primary Cells (non-rechargeable) and Secondary Cells (rechargeable)

    • Main battery applications:

      • Radio and inter-communication
      • Fuel controls
      • Vital instrumentation
      • Fire extinguishing
      • Standby lighting
      • Other vital functions

    • Battery types: Acid (Lead-acid) and Alkaline (Nickel-cadmium)### Lead Acid Batteries

    • Main elements: positive (lead peroxide) and negative plates (pure lead) dipped in dilute sulfuric acid electrolyte solution

    • When fully charged, off-load voltage and electrolyte specific gravity are high

    • Charge current falls to zero near full charge

    • Voltage decreases under load, but must not fall below 22.5 Volts under prescribed test conditions

    • Nominal voltage of a lead-acid cell is 2 V, so twelve cells are needed for 24 V

    • If a cell voltage falls below 1.8 V under specified workshop load test conditions, it is discarded for aviation applications

    Nickel Cadmium (Ni-Cd) Batteries

    • Plates are nickel hydroxide (positive) and cadmium hydroxide (negative)
    • Electrolyte is a solution of potassium hydroxide (KOH) in distilled water
    • An aircraft charger (BCL - Battery Charge Limiter) reduces overcharging by regulating the duration of charge current
    • Overcharging leads to water loss from the cells, which can damage the battery if the electrolyte level falls below the top of the plates
    • A thermostat mounted on a battery link controls the charger to prevent overheating
    • The battery charger prevents sleepiness of the batteries, which occurs when exposed to abnormal charge and discharge cycles
    • Advantages: longer life span, constant voltage during discharge, and minimal voltage drop under heavy loads
    • Disadvantages: more sensitive to thermal runaway, requires special charger to avoid sleepiness

    Thermal Runaway

    • A condition that occurs when a heavy charge current flows in warm conditions
    • Lead-acid batteries are normally constant voltage charged, so the charge current increases as rising temperature causes internal resistance to fall
    • This generates more heat, further reducing resistance, and causing over-heating of the cells
    • Batteries are located in areas where they will create minimal damage to aircraft structures and components in case of thermal runaway

    Safety Precautions and First Aid

    • If electrolyte is splashed on skin or eyes: rinse with water, seek medical attention, and neutralize with vinegar or boric acid solution
    • If electrolyte is spilled on metal: soak up with sawdust, neutralize with bicarbonate of soda or boric acid solution, and thoroughly wash and dry
    • If electrolyte is spilled on fabric: dab with ammonia or boric acid solution, rinse with water, and replace if necessary

    DC Power Generation

    • Main power system on large commercial aircraft is A.C., but D.C. is used for emergency/standby supplies
    • DC generators are not fitted on most commercial aircraft
    • Light aircraft and some larger turbo-prop types require a different approach

    DC Generator

    • Should be able to supply full power at constant voltage over the operational speed range of the engine
    • Aircraft DC generators are self-excited, with a voltage regulator to maintain steady output voltage
    • The field current is tapped from the generator output, making the generator effectively self-contained and independent of other supplies

    AC Power Generation

    • A.C. supplies are used on commercial aircraft due to the need for high and constant frequency/voltage
    • A.C. can be readily transformed with minimal losses, and alternators can simultaneously give different outputs
    • Cable weight and voltage drop can be minimized by using A.C.
    • A.C. motors are more reliable at high altitudes and at temperature extremes

    Alternator

    • A constant frequency alternator on the aircraft has to support full load at constant voltage and frequency regardless of engine speed
    • Commercial aircraft have 30-90 KVA continuous rated generators
    • Ratings of 150 KVA + are used on some military aircraft
    • Achieving high performance depends on efficient cooling and "brushless" design

    Brushless Alternator

    • Magnets induce three-phase A.C. in rotor "A.C. exciter" windings
    • The three-phase is full-wave rectified by diodes to give a rotating D.C. field
    • Three-phase A.C. is induced in stator "output" armature windings
    • The transformed output is rectified and regulated to D.C.
    • D.C. is applied to the stationary exciter

    Control and Protection

    • Features are necessary to isolate the faulty part, like the generator
    • Control and protection may include simple devices like fuses and circuit breakers or elaborate electronic circuits
    • Reverse current protection, overvoltage protection, and under voltage protection may be incorporated
    • Frequency wild alternator systems were commonly used before CSD development

    Starter-Generators

    • Fitted to some DC powered aircraft to save cable and component weight
    • They are permanently coupled via a drive shaft and gear train
    • For starting, it runs as a fully compounded motor with the shunt winding supplied via a field change-over relay
    • When the relay is de-energized, it connects the shunt field to the voltage regulator### Electrical and Avionics
    • Differential protection system: uses two transformers (hot and cold) to detect short circuits in the protected zone (generator, wiring, or GB/BTB)
    • Line to line fault protection: if a short circuit occurs, the two generated phases connected by the fault will have a potential difference, causing current flow between them, which is unlikely to reach the distribution point
    • Over-current protection: supplements the differential protection system to trip the G.B. if the system places excessive load on the generator
    • Three additional current transformers may be fitted to monitor the current of each phase (or the "hot" differential transformers may serve a dual role)

    Emergency Power Generation

    • The A320 uses an emergency generator called CSM/G (Constant Speed Motor/Generator)
    • The CSM/G is driven by the blue hydraulic system via the Ram Air Turbine when the electrical emergency condition is met
    • The Ram Air Turbine has no internal generator, it only provides hydraulic pressure (blue system) to the CSM/G
    • The A320 emergency generator can be configured to automatically deploy the Ram Air Turbine if AC BUS 1 and 2 are lost above a given airspeed (100 kts)

    A320 Electrical System Emergency Configuration (Overview)

    • If AC BUS 1 and 2 are lost, the Ram Air Turbine will extend automatically
    • The AC ESSential BUS and DC ESS BUS are respectively supplied by the STATic INVerter and battery 2
    • The emergency generator via the blue hydraulic system takes place only if the landing gear is not compressed
    • When the emergency generator is available, it supplies the AC ESS BUS and via ESS Transformer Rectifier (TR), the DC ESS BUS

    Rat Generator (B777)

    • The Ram Air Turbine (RAT) generator supplies 115 Volts three-phase emergency AC power when normal power sources are not available
    • The generator has a capacity of 7.5 KVA
    • The frequency range is from 392 Hz to 510 Hz

    Transformers and Rectifiers

    • Roles of transformers:
      • Increasing voltage to supply fluorescent tubes
      • Supplying 28 V.A.C. bus bars (mainly for lights and instruments)
      • Supplies "built-in" to avionic equipment
      • Monitoring voltage or current for control or indication ("metering")
      • Saving cable weight by "stepping down" with local transformers at equipment
    • Roles of rectifiers:
      • "BLOCKING": isolation of one circuit from another whilst allowing a common function to be served
      • D.C. supply: stepping down by transformers and then rectifying in combined transformer/rectifier units (TRU) to supply 28V.D.C. bus bars for battery charging and other D.C. loads

    Power Distribution

    • Multi-generator distribution: a typical switchgear arrangement to connect alternators to loads
    • Non-paralleled system: operates with the (GB,GCB)GLC's closed and the (BTB)BTC's open
    • Paralleled and synchronized system: most constant frequency aircraft systems have a synchronized bus bar system, with loads equally shared by each alternator

    External/Ground Power

    • The connected light illuminates when the truck supply is available on the aircraft
    • The truck supply is connected to the aircraft through a relay on the truck and a switch on the truck
    • The truck's relay should disengage before the three-phase supply pins' contact is broken

    Later Generation System Example

    • Modern aircraft combines the CSD and Generator into an integrated unit called Integrated Drive Generator (IDG)
    • The A320 is equipped with two IDGs
    • The generator portion delivers 3 phase, 400 Hz, 115 Volts ac at 90 KVA
    • The CSD portion maintains the generator at a constant 12,000 rpm during normal operating conditions

    No Break Power Transfer (NBPT)

    • Allows transfer of supply from one generator to another without any power interruptions
    • Two generators are allowed to be synchronized for a very short period of time before one of them disengages to allow transferring of supply without any interruptions

    Pitot-Static System

    • Senses the total pressure generated as a result of forward movement of the aircraft and the static pressure of the atmosphere surrounding it
    • Outputs these data to different instruments in terms of speed, altitude, and rate of change of altitude (vertical speed)

    Basic Pitot-Static System

    • Consists of a pitot-static tube (combination), or pressure head, three primary flight instruments (airspeed indicator, altimeter, and vertical speed indicator), and interconnected pipelines and drains

    Pitot-Static Tube (Principle)

    • Supplies the dynamic (pitot) and/or static pressure to the airspeed indicator, altimeter, vertical speed indicator, and Mach meter
    • Installed outside the aircraft in a region of undisturbed air (near the nose or leading edges)

    Static Vents

    • Air disturbances causes the static-pressure measuring section of a pitot-static system to measure higher pressure than free-stream static pressure, resulting in what is known as a position error
    • Hence, the straightforward and logical solution is to remove them from the pitot probe and locate elsewhere on the aircraft
    • The static vent for some light aircraft is simply a hole drilled in the fuselage skin, while for more complex aircraft systems specially contoured metal vent plates are fitted to the skin

    Altimeter

    • Indicates the altitude at which an airplane is flying by measuring atmospheric pressure
    • Similar to an aneroid barometer
    • The height of the column of air above an aircraft decreases as an aircraft climbs away from the earth's surface
    • The weight of the column decreases and hence exerts less pressure; therefore, atmospheric pressure decreases with height

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