Systems PT1

Question 1

what is the function of the electrical system on a large transport aircraft?

Answer 1

generate, regulate and distribute electrical power throughout the aircraft

Question 2

how many electrical systems are there

Answer 2

there is usually more than one system and comprise of a mixture of AC and DC circuits

Question 3

what is the normal config of a electrical system

Answer 3

will have a separate AC circuit powered by the alternator fitted to each engine and each circuit will feed a specific bus

Question 4

why is AC more common in use than DC

Answer 4

AC alternators are more light than DC generators of similar capacity

Question 5

explain the basic bus system

Answer 5

power supply is routed to a common bar, off which several components or services can be powered.

this splits the electrical system into channels so that some parts can be prioritized in the event of a supply breakdown

Question 6

what are the different types of bus system

Answer 6

parallel type
split bus type
split parallel type

Question 7

how is DC power provided on an aircraft

Answer 7

AC power is rectified using a full wave rectifier
(AC can be produced from DC using an INVERTER also)

DC circuits have their own bus system isolating them from the AC bus

Question 8

what must be determined before AC generators are connected in parallel

Answer 8

output voltage, frequency, and phase rotation are the same

Question 9

how does emergency lighting work in an aircraft

Answer 9

it’s armed and will automatically activate after the failure of primary lighting power

Question 10

explain how the CSD works

Answer 10

the AC alternator requires power at a constant 400hz. the frequency is determined by the rotation speed of the armature, which is driven by the engine. The engine however doesn’t output a constant speed so a constant frequency can’t be delivered unless a device (CSD) is installed so that no matter what the speed of the engine is, the alternator can still output 400hz.

Question 11

explain the implications of generator failure

Answer 11

in an electrical fault, the circuit breakers protect the system, however a mechanical failure can cause serious engine damage is rotation is not stopped

The GEN DISC switch disconnects the engine drive from the gearbox and CSD using a DOG CLUTCH and cannot be reset after broken

Question 12

what are CSDs that are built into generators called

Answer 12

IDG (Boeing) integrated drive generator

ICSD (airbus) integrated constant speed drive

Question 13

what purposes do air conditioning and pressurisation have on an aircraft

Answer 13

• conditioned air for heating/cooling cabin/cockpit
• prevent condensation on a/c equipment and protect avionics
• provide conditioning for cargo as animals sometimes stored

Question 14

what is PD

Answer 14

pressure differential, the difference between pressure inside the hull and the ambient pressure.

the system maintains a cabin alt of 8,000ft regardless of the altitude the aircraft is flying. if the a/c climbs beyond 8,000ft then PD will increase

Question 15

how is PD controlled

Answer 15

controlling outflow of air from the fuselage. as air con flows in, the outflow is regulated at a lesser rate by a a rate controller. it also controls cabin VS.

when desired PD is achieved, outflow is increased again at a rate that will maintain the desired PD level

Question 16

how does the outflow valve work?

Answer 16

outflow valve position is controlled by a cabin pressure controller either automatically or manually w a target of 8.9 PSI diff.

Question 17

how is the environmental system controlled from the cockpit

Answer 17

simple systems have a OFF-NORMAL-RAM setting

most modern aircraft have a panel where individual temps can be set in the cabin and cockpit.
- also will have individual pressure controls on the panel incl. emergency controls and warning lights

Question 18

what are the safety features of the environmental system

Answer 18

• pressure control valve
• pressure relief valve (used to ensure pressure does not build up beyond max operating pressure)
• negative pressure valve ( ensures pressure outside cabin never exceeds pressure inside the cabin and operates automatically
• emergency depressurisation valve (activated by WOW switch)
• emergency cabin altitude control

Question 19

explain how vapor cycle air conditioning works

Answer 19

on the principle of latent heat

the refrigerant changes state from liquid to vapor, and in doing so absorbs heat from the cabin. this heat is sent outside the aircraft as the refrigerant returns to a liquid state.

Question 20

explain the requirements and behavior of refrigerants

Answer 20

almost any liquid can be a refrigerant

for max effectiveness:
- low vapor pressure and boiling point

Question 21

how does the continuous flow oxygen system work

Answer 21

• used in the cabin where it is automatically actuated and a flow of oxygen is immediate and continuous

Question 22

how does the pressure demand oxygen system work

Answer 22

has a diluter demand regulator, which delivers oxygen to persons lungs when person sucks in to breathe.

oxygen is automatically diluted in regulator with some atmospheric air which only takes place below 34,000ft

found on the flight deck where it is more essential for the crew to be functioning than the cabin until the aircraft gets down to a safe altitude

Question 23

when is 100% oxygen used?

Answer 23

in the event of smoke or other contaminants in the cockpit

Question 24

what is the requirement for oxygen supply on large transport aircraft

Answer 24

enough for the aircraft to descend from cruising altitude to 14,000ft in less than 4 minutes without exhausting the oxygen supply

Question 25

what are the advantages and disadvantages of chemical oxygen systems

Answer 25

advantages:
- lightweight
- less equipment
- less maintenance

disadvantages:

• fire hazard higher
• not tamperproof
• won’t turn off

Question 26

what systems protect an aircraft from fire

Answer 26

overheat, smoke and fire protection systems

Question 27

a complete fire protection system includes:

Answer 27

fire detection and fire extinguishing systems

Question 28

what are the characteristics of automatically fired extinguishing systems? where are they found?

Answer 28

usually found in toilets

• the fire bottle is fitted with a squib which melts at 70-75 degrees, allowing the extinguishing agent to exit the bottle

Question 29

what are the 4 types of extinguishing agents

Answer 29

1. Water (cools fire and excludes oxygen)
2. carbon dioxide (displaces surrounding oxygen)
3. dry chemical (smothers the fire excluding oxygen)
4. halogenated hydrocarbons (chemically interferes with combustion)

Question 30

how does the pneumatic fire protection system work

Answer 30

a gas inside tube inside a cylinder expands when heated. when the trigger temp is reached, the gas pressure moves the tube (check valve) which hits the alarm contact causing the alarm to sound.

when the temp falls below the trigger temp, the valve will move back into place and can be used again.

Question 31

how does the smoke detector work

Answer 31

uses photoelectric cells with a light beam directed toward them. if enough smoke is present, the light beam refracts light to the cells causing the alarm to sound.

Question 32

how does fire extinguishing work inside the engine nacelle

Answer 32

• bottle is powered at 500-600psi.
• has a relief valve that will rupture if the bottle were to overheat
• the bottle is discharged from the cockpit by an electrical current applied to contactor which detonates an explosive cartridge and shatters a disk at the bottle outlet letting the agent flow

Question 33

what speed do turbine engines spin at

Answer 33

7,000-10,000 rpm

Question 34

why is halon 1301 the ideal agent used for fire extinguishing in the air

Answer 34

• low concentration and very effective
• may be used in occupied personal compartments
• effective on all 3 fire types
• no residue remaining after use

Question 35

how does fire extinguishing work in the engine nacelle

Answer 35

• fire bottle pressurized to 500-600 psi
• relief valve is a fusible disk that will rupture if bottle overheats
• electrical current is applied to contactor which detonates an explosive cartridge which shatters a disk in the bottle outlet, allowing the agent to flow

Question 36

what callouts are there for lockout system failures

Answer 36

• rudder ratio
• all lock
• EICAS

Question 37

when are high lift devices employed

Answer 37

only at low speeds

form part of aerofoil when not in use

Question 38

what are the common lift augmentation devices

Answer 38

• slot, slat flaps (LE and TE), fowler flaps

Question 39

what is the problem of the power boosted control system

Answer 39

during transonic flight, shock waves form on control surfaces causing buffeting

Question 40

how are buffeting forces dampened

Answer 40

power operated irreversible control system

cockpit controls actuate control valves which direct hydraulic fluid to control surface actuators (PCU)

• artificial load is built into the system so pilot has more control feel

Question 41

how does the fly by wire system work

Answer 41

crew command inputs are translated into electrical signals

signals go to actuator control electronics

signals converted to digital format and sent to primary flight computer

inputs are analyzed, and if outside flight control envelope the signals are modified so they stay inside

can be operated with IFS providing auto flight control and feed flight control data to the FDC