aircraft auxilary electrical systems

Question 1

briefly explain the system of the colours used in the CWS

Answer 1

captions are red for important failure,

amber for cautionary failures and

green for advisory information

Question 2

9 steps

explain how first line test is carried out on the CWS

Answer 2

1. press test button
2. checks all captions illumiminate
3. check every filament is servicable
4. ensure attention getters operate
5. check cancel facility
6. check audio warning operates
7. check dimming switch
8. release test button
9. ensure all lights that should extinguish do

Question 3

how is the pilot made aware of important aircraft system failures

Answer 3

red warning captions

accompanied by flashing attention getters

and an audio tone

Question 4

list 5 different types of sensors used to detect system faults

Answer 4

pressure switch

micro switch

thermal switch

relay contacts

limit switch

firewire

Question 5

describe the construction of the fire wire element

Answer 5

stainless steel tube surrounding an aluminium oxide sintered glass coating for the central electrode nickel chromium steel conductor

Question 6

explain how the fire wire in No 1 engine is detected by the firewire and indicated to the pilot

Answer 6

a fire would cause the impedance of the fire wire to decrease,

this would increase the amplitude of the detector waveform relative to the reference waveform of the control unit,

causing a relay in the control unit to energised, sending a signal in the AMS

the AMS will cause a ENG BAY 1 FIRE caption to illuminate on the WCA and attention getters to flash on the MWL

the ENG 1 lamp and switch 1 lamp will also illuminate, and an audio tone will sound in pilots helmet

Question 7

explain how the flotation circuits react when electrical power is applied and the MASS and flotation switches set to live and armed

Answer 7

power on causes flot armed relays to 1,2,3 and flot degrade relay to energise

PSU capacitors will charge up and green LEDs will illuminate

MASS and flot switches will allow man/auto operation of flot system

Question 8

explain how the flot system is auto activated (even with the MASS set to safe)

Answer 8

the flot will activate when the PSU senses water for 2.5 secs

this will cause the flot bottles to be fired by the crossfire circuit and all flotation bags to be inflated

with the rear bags inflating 3 secs before fwd bags to prevent damage to fwd bags

Question 9

explain the need for NVG lighting

Answer 9

used for tactical flying at night and to prevent pilots being blinded by internal lights

Question 10

what is the difference between active and passive lights

Answer 10

active lights illuminate the legends on push buttons that show a change in status or selection

passive lights illuminate background labels, names and switches

Question 11

explain how the pilots/co-pilots wipers can be operated in intermittent mode

fast

slow

Answer 11

w/s wipers switch set to both wiper rotary control switch selected to (intermittent, fast or slow) mode

wiper motor relays energise, contacts change over and feed AC power to w/s wiper motor

the ECU controls the speed of the wipers and intermittent setting

Question 12

explain how ice and snow is detected by the ice and snow detection system (ISDS) and how the severity is displayed to the pilot

Answer 12

during iceing conditions air passes through the measuing head, forming ice on the bar

the rate at witch ice forms is measured by infra red sensors whose beam path becomes obstructed by ice forming

when an upper limit is reach, the bar is heated to melt off the ice and process is repeated

snow is detected using the same beams becoming temporarily obstructed

ice is indicated by the word ICE in yellow on the PFD

Yellow with box around the word ICE shows moderate build up

Red ICE with box shows severe icing

snow is shown in the same manner and if there is ice and snow together ICE/SNOW is indicated in the same boxes

Question 13

using the diagram explain pitot anti icing system when pitot systems are switched on

Answer 13

the heater monitor units control the current flowing in each of the four heater circuits,

the heater elements have a positive temp coefficient and are self regulating

Question 14

pitot anti icing when on the ground

Answer 14

the pitot strut heating is inhibited on the ground by the WOW relay which prevents possible overheating in still air

Question 15

pitot anti ice when faults are detected and how are they displayed

Answer 15

the heater monitor units monitor the current flowing in each of the four heater circuits

if the current drops below pre-determined levels, failure signal are fed to the AMS

the fault is diplayed on the SMD WCA window

Question 16

diagram

fully explain the operation of the undercarriage system and the indication from the time that the pilot selects undercarriage down and the aircraft landing

Answer 16

when the undercarriage control lever is selected down, the control valve down solenoid is energised and the hyds pressure is fed to remove the uplocks and lower the undercarriage

during transiton the red u/c indicators lights will illuminate

when the u/c is fully down and locked the down lock microswitch causes downlock relay contacts to change over to the lock position

green indicator light illuminate and hyds will be removed form the u/c system

when the aircraft is back on the ground, the WOW microswitch will change over and the u/c control solenoid will lock down

Question 17

diagram

Expalin how the ECS keeps cockpit and cabin air temp controlled

Answer 17

master switch on ECS control panel selected on (auto pos) and the cockpit temp selected by the pilot using the temp control switch

the digital controller (14) controls the operation of the valves according to the pilots selection and inputs from temp sensors

the conditioned air from the cooling pack (7) is fed through the distribution ducting to the cockpit (12) the mission booth and rear cabin

hot air is mixed with the cool air by the temp control valve (8) according to the cockpit temp inlet and outlet sensors (10,11)

the temp selector is a manually controlled potentiometer, normally the setting will be within the AUTO selector and the cockpit temp will be kept at the selected datum

reversionary selection is available if a fault develops in the auto system allowing manual override

Question 18

explain how the components purpose of the tail lock actuator and its indication flag

Answer 18

the tail lock actuator is used to lock and unlock the tail extension or extraction of the spade locks which extends into the tail lugs

extraction of the locks causes the ‘PIN OUT’ flag to show that spades are unlocked

Question 19

explain the purpose of the tail fold actuator and its mechanical drive option and microswitch

Answer 19

tail fold actuator on the tail hinge is used to fold and spread the tail

a mechanical drive on the actuator body can be used in the event of an electrical failure

two microswitches (fitted on the upper part of the tail top hinge) are used to indicate to the FMU that the tail is fully folded or fully spread

Question 20

briefly explain the ACSR

Answer 20

active control of structural response is a vibration reduction system

sensors are mounted at key locations on the airframe to monitor vibration and feed signals to an ACSR

ACSR causes the actuators within the gearbox struts to vibrate in opposition to the original vibration thereby cancelling the original vibration

Question 21

diagram

state the occasions when a BIT test is carried out on the rotor break

Answer 21

BIT test is carried out whenever the test switch on the rotor break control panel is pressed and when the rotor brake handle is repositioned (selected from (off to on)

Question 22

when the FAIL caption illuminates on the rotor brake control panel

Answer 22

if any of the rotor brake component are unservicable a FAIL caption will illuminate on the RBCP

Question 23

when will an INHIBIT caption illuminate on the rotor break control panel

Answer 23

if any of the systems, engines or WOW interlocks are incorrect then an INHIBIT caption will illuminate on the RBCP

Question 24

briefly describe 4 (of the possible 7) electrical sensors of fault switches fitted to the No 3 IHPS and how each fault or indication is displayed

Answer 24

oil pressure transducer and oil temp sensors, displayed on SMP and SPSD

displayed as a yellow caution caption on the WCA window;

hot oil (HYD HOT)

oil high level switch (HYD MAX)

oil low level switch (HYDS LOW)

oil alert level switch (HYDS ALT)

oil refil level switch (HYDS RF)

Question 25

# diagram state the type of extingusher used and how it works to extingush the fire

Answer 25

halon 1301 an (BTM) bromotrifluromethane works to cool the engine compartment and remove oxygen

Question 26

# diagram state how many fire bottle are fitted in the merlin and how they are allocated

Answer 26

4 bottles with a cross feed system linking the engines and bottles bottle 1 + 3 feed to ENG 1 + 3 Bottle 2 + APU feed to ENG 2 + APU

Question 27

# diagram explain the operation of the fire bottle circuit for No 1 and No3 engines if the inertia switch operates (include the effect of the Xfeed/manual switch)

Answer 27

if No1 **crash switch** operates, all **crash relays** will **energise** and after a short delay, their **contacts change** over to supply **power to energise** all **normal relays** and all **crossfeed relays** if the xfeed/normal switch is **normal**, the **normal cartridge fires** in each fire bottle, if set to **xfeed** the **xfeed cartridge fires** in each fire bottle when the **pressure** in the fire extinguisher bottles **decrease**, the **low pressure switch operates** causing the **low pressure indicators** to illuminate

Question 28

explain how the purpose of egress lighting and where it is fitted

Answer 28

egress lights are strips **fitted** around the **cockpit, cabin doors and release handles** they will **illuminate** in the event of a **crash or** **ditching** to indicate the emergency **exits**

Question 29

how is egress lighting powered and activated

Answer 29

powered by individual **batteries** operated **manually/automatically** by **inertia** switches **water** activated switches **loss of power**

Question 30

# diagram (rotor ice protection unit) describe how the heater matts are arranged

Answer 30

**two sections** an **inner** and an outer with **5 metallic heater elements** embedded between layers of **GRP**

Question 31

RIPU explain how and why the power is fed to them in a controlled sequence

Answer 31

the RIPU feeds **electrical power via a slip ring assembly** to the same **heater element** of **each** main rotor **blade simultaneously** and in a **cyclic sequence** to each group of heaters to provide **symmetrical ice shedding**

Question 32

# diagram explain the operation of the RIPU system when switched on and selected to auto

Answer 32

when RIPU is switched **on**, the master **contactors are energised** and the RIPU **fans run up**, the system then performs a **self test** and if satisfactory puts system into **standby** when temp below **0ºC** the system **automatically comes on**, and **power is applied** by the controllers to the **heater elements** in the **sequence** according to the weather condition from the **OATs** if the system goes above 0ºC the system will revert to standby

Question 33

explain the operation of the RIPU system when switched on and selected to manual

Answer 33

pressing the **man/fail** button on the ice protection panel will cause the **manual caption to illuminate** and the **controller will supply power** to the main rotors **in sequence** determined by the **OATs** but there will be **no off time** between sequences in **both modes** of operation the controller feeds a **constant supply** of power to the **tail rotor**

Question 34

RIPU when the test switch is operated

Answer 34

when the **test switch is operated** a **full test** is carried out, the rotor ice **fail caption illuminates** on the WCA window and **fail lamp on the anti ice panel**. all lights are extingushed when a satisfactory test is complete

Question 35

# diagram explain how the undercarriage is prevented from retracting on the ground

Answer 35

the undercarriage **control lever** is **locked** in the **down position** by the **WOW** microswitchs when the aircraft is on the **ground** and by the use of **ground lock safety pins**

Question 36

how is the pilot made aware that the undercarriage is up when coming to land

Answer 36

if the aircraft is **below 30 ft** (RAD ALT) with **landing gear retracted** the CDS will display a **LANDING GEAR caution** caption and an **audio warning** wheels wheels will be heard by the pilot

Question 37

what lights are used to show the pilot and ground crew that the aircraft is safe to land

Answer 37

**undercarriage panel and U/C repeater lights should be showing three greens.** lights illuminate don either side of the nose wheel to indicate to ground crew that the U/C is down and locked

Question 38

what facility is used if the undercarriage fails to extend by normal means and how is it operated

Answer 38

if the normal method fails, the **emergency selector** is pressed and rotated to the **DOWN EMERGENCY position.** **EMERG DOWN indicator** will **illuminate** on the instrument **panel repeater group**

Question 39

# diagram Explain the switch selection options of the ECS switching panel

Answer 39

there are 3 AVCS and ACCS fans, fan selction is 1/2, 2/3 and 1/3 only two fans can be selected at one time air is drawn in through ACCS inlet and vent through the ACCS exhaust the third fan is available if either of the other two fail AIR SWITCH has 3 pos RECIRC/AUTO/AMBT this controls the recirculated air CREW FAN switch manual selection of the crew fan on/off MASTER SWITCH has 3 pos marked ON/OFF/REV on is auto and REV is manual TEMP SELECTOR is a manually controlled potentiometer, normally the setting will be within AUTO sector and cockpit, temp will be kept at datum REV selection is available if a fault develops in the auto system allowing a manual override

Question 40

# diagram with reference to the blade fold system fully explain the purpose of the rotor index actuator

Answer 40

this consist of a linear actuator which extends to engage with the main gearbox rotary actuator motor which turns the main rotor head to align No1 main rotor blade (RED BLADE) 3 degrees to the left of the tail

Question 41

with reference to the blade fold system fully explain the purpose of the blade fold actuator

Answer 41

blade fold actuators consist of a **linear actuator** which is used to **insert and withdraw** the blade **lock pins** and a **rotary actuator** which is used to **fold and spread** the main rotor **blades**

Question 42

# diagram with reference to the blade fold system fully explain the purpose of the main rotor head resolver

Answer 42

main rotor head resolver provides position info of the main rotor head to the FMU

Question 43

briefly explain the transmission vibration monitoring system (TVM) used in the transmission gearboxes

Answer 43

the TVM system consist of **accelermoneters and azimuth sensors** fitted on the transmission **gearboxes** which sense any **vibration** vibration **signal** are fed to the **VDAM** in the **AMMC** if vibration exceeds a threshold **limit,** a **caution** caption will **display** on the WCA

Question 44

# diagram describe all indications displayed to the pilot relative to the position and condition of the rotor brake system

Answer 44

RBCP has a **gated lever** marked **ON OFF PRK** and **displays** the **RTR BRK ON INHIBIT FAIL** indications RB system **info** is displayed on the **left** hand side window of the **SMP** RB system **faults and advice** are displayed as **caution captions and advisory captions** on the WCA

Question 45

5 precautions when servicing fire wire

Answer 45

when a fire wire is disconmected protective caps must be fitted elements found uncapped must be treated as contaminated grease must be kept clear of the couplings when reconnected, new copper crush washers must be fitted all firewire couplimg must be correctly torque loaded all bends must exceed 1" radius bends must not commence less then half an inch from any clip or connection replacement elements must be off the correct type securing clips should be no more than half inches apart an insulation test must be carried out for the minimum time to prevent polarisation of the fire wire element

Question 46

3 precations of the external aircraft lighting system

Answer 46

anti-coll lights **can blind** if too close white anti-coll lights and **ultra violet radiation** can **damage eyes** at less than **2 mtrs** **do not** switch on anti-coll lights **without** the **glass head fitted**, as this provides complete **protection** from ulta violet due to the **height** of the anti-coll lights ensure correct staging is used with **raised guards** ensure **power is removed** from anti-coll lights due to the high power **capacitor used**, and wait **2 mins** before working on them **steerable landing lights** are powerful and **damage** to the **filament** can occure if operated facing **downwards** steerable landing light is **extremely hot** ensure no combustable **material** is present when operating

Question 47

EA system when switched off

Answer 47

when the **master** switch is **off**, the **engine select switch and the bleed valve select switch** are all **off**, **no heat** is applied to the intake **mats** the engine **bleed valve** will be energised **close** and **no hot air** is fed into the **engine**

Question 48

EA is switched on with manual control set

Answer 48

system on, all engine **air-intake** and **bleed valves** switch/indicators are set to **on** when the master switch is set to the **MAN position,** the **manual control relay will energise** and the **bleed valve will de-energise** in the open position and will remain **open continuously** the anti-ice **control** will monitor and control the **electrical supply** to the intake **mats,** keeping the **intake surfaces** within the range of **60\*C to 140\*C**

Question 49

explain operation of EA system when auto control set

Answer 49

if engine ant-ice master switch is set to the auto position the AMS will control the DC supply fed to the anti-ice controller and bleed valves according to the outside temp if outside temp drops below 6ºC the auto control relay will energise, causing the bleed valve control relay to energise, removing the supply to the bleed valve which opens to allow the hot air into the engine

Question 50

explain operation of EA system when system is tested

Answer 50

the system can be tested by selecting the **test switch to TEST** this will cause **A/ICE TEMP A/ICE HOT A/ICE HEAT captions** to be displayed on the WCA window and the **fail lamps** to illuminate on the **intake and bleed switches** all lights should **extinguish after 5 sec** any lights that **remain on indicate a fault**

Question 51

# diagram explain pilots andf co pilots wash bottle operation

Answer 51

when the windscreen is selected to fast or slow and the washer bottle relay will be energised its contacts will be in position to allow DC power to the washer bottle pump, then operated by pressing the pilot/co-pilots cyclic wash/wipe push switch

Question 52

# diagram explain the undercarriage test facility

Answer 52

selecting the test switch on the control panel green, red and yellow indicator lights should illuminate on the control panel repeater display

Question 53

explain the purpose of the ECS

Answer 53

environmental control system provides cockpit and cabin ventilation, cooling and heating consists

Question 54

briefly explain the six system of the ECS

Answer 54

instrument panel radar cooling avionics cabinet mission console (displays and LRU's) active dipping sonar (if notfitted becomes troop cooling) compartment conditioning (cooling and heating)

Question 55

how is the rotor brake selected, operated and powered

Answer 55

the rotor brake is selected by the control lever, electrically operated and hydraulically powered

Question 56

explain how operation of the rotor brake is normally prevented from operating in the air and in what emergency circumstances could this normal prevention be overridden

Answer 56

operation of the rotor brake when the aircraft is airborne is normally prevented by the WOW switched, WOW override switch allows operation of the rotor brake if the aircraft is to ditch in water or if the WOW switch fails

Question 57

how many hydraulic pumps are fitted in a modern helicopter and explain how they are driven and what system they supply

Answer 57

there are **3 hyds pumps** used to supply 3 hyds systems 1,2,3 they are driven by the **main gearbox** and the **accessory gearbox** **hyds systems 1,2** feed the **flying controls** and if one systems fails the other will continue to do the work **hyds system 3** normally **feeds** the aircraft system which are the **rotor brake, sonar winch, rescur hoist, ACRS, decklock, nosewheel stearing, landing gear and brakes,** but will crossfeed into systems 1 and 2 in emergency

Question 58

explain operation when pilot fires both extinguishers into No1 ECU

Answer 58

fire occures in No 1 ENG (1 FIRE) indication illuminates if Xfeed/normal switch is normal, Normal 1 relay will energise and fire normal cartridge in No 1 engine fire extinguisher bottle when the cartridge fires, it ruptures the frangible disc in the discharge outlet of the fire extinguisher bottle allowing the extinguishant to be released into the engine No 1 bay when the pressure decreases the low pressure switch operates causing the low pressure indicator to illuminate if fire is not extinguished by the normal system, the xfeed/normal switch is selected to xfeed. the same switch/indicator is pressed and energises the crossfeed relay, the Xfeed cartridges (ENG 1) in No 3 engine fire extinguisher bottle and the contents of No 3 bottle is discharged into No 1 engine bay when the pressure i No 3 fire extinguisher bottle decreases, the low pressure switch operates causing the low pressure indicator illuminate

Question 59

normal operation of windscreen de-icing

Answer 59

pilots/co-pilots w/s controllers energise w/s heating and overheat relays, this feeds 3 phase AC power to w/s heater elements, the normal sensors cycle heaters on at 24\*C and off at 30\*C by de-energising the relays at the temps keeping the w/s free of ice

Question 60

name and number the components of the blade fold system

Answer 60

1. FMU 2. bladefold control panel 3. rotor index actuator 4. swash plate actuator (FCPA) 5. blade fold actuator x 5 6. rotor head resolver 7. tail lock actuator 8. tail fold actuator 9. pitch lock rotating actuators x 3 10. pitch lock linear actuator x 3

Question 61

briefly explain the QDM system of the transmission system

Answer 61

QDM uses sensors inside the **gearbox** which constantly **monitors** the **circulating oil** in the gearbox for **ferrous** debris particles the sensors retain any particles collected and feed **detection signals** to the **AMS** for data recording and will initiate a **caution** caption on the WCA window if a threshold **limit is reached**

Question 62

explain how supply failure to one PSU would affect the system

Answer 62

loss of power to a PSU due to broken wire or PSU means that the PSU could not initiate auto-op, the fault would cause relay 1-2-3 to de-energise causing the flot degrade relay to de-energise and an earth loss would cause the 'flot degrade' caption to illuminate on WCA manual operation is unnaffected by loss of PSU and remaining PSU's would still fire manually

Question 63

summarise the test procedure carried out on the flotation circuits

Answer 63

disconnect all operating heads fit test lamps to disconnected head disconnect the submersion actuators switch on 28 volts DC switch ESSB to live operate manual flot switch and check that all test lamps illuminate carry out a no vaults checks reconnect the submersion actuators select ESSB to safe remove the earthing caps and reconnect the operating heads

Question 64

explian the operation of the BLADE/FOLD/TAIL switch

Answer 64

selects operation of main blades only, tail only or both blades

Question 65

explain the FOLD/OFF/SPRD switch

Answer 65

selects operation of fold cycle or spread cycle

Question 66

explain purpose of the master switch

Answer 66

on off switch which feeds electrical power to the system

Question 67

fully explain the four indication/captions that illuminate on the blade fold control panel

Answer 67

the on light illuminate when master switch is pressed once, extinguishes when pressed a second time secure light will illuminate when FMU has performed a 12 sec installation (after the master switch has been pressed) it will also illuminate after a fold or spread operation has been completed fail light will illuminate when ever system develops a fault

Question 68

what is the construction of the pilots and co-pilots windscreen

Answer 68

laminated screen with metal-oxide film heater 3 temp sensors windscreen heating is selected by switches on the w/s control interseat panel

Question 69

purpose of static discharge box

Answer 69

static discharge boxes are fitted in the system to prevent build up of static when w/s heating is off

Question 70

explain w/s operation if one of the normal sensors fails

Answer 70

if the normal sensors fail, the affected w/s will heat up to 50\*C, the combined effect of the overheat sensors will cause the w/s to cycle on at 44\*C and off at 50\*C

Question 71

explain the w/s test facility

Answer 71

when the w/s test button is selected to A/B the w/s test relay is energised and contacts change over to test overheat sensor circuit A or B during the test discrete logic signals are fed to the AMS

Question 72

describe the purpose of the rotor brake on a modern helicopter with automatic bladefold

Answer 72

stop rotors during normal engine shutdown or during an emergency, when parked with blades spread used during automatic blade fold and spread cycles to allow positioning of the blades as required

Question 73

briefly describe the purpose of the hydraulic control panel

Answer 73

used to make switch selections and test change over valves and display system indication

Question 74

what is the purpose of the change over solenoid valve

Answer 74

allows the hydraulic system o be routed to thier correct system during normal operations and during faults

Question 75

electrical pump (AUX PUMP)

Answer 75

used during ground maintenance operations and to charge the accumulator

Question 76

purpose of the accumulator

Answer 76

provides emergency pressure for the rotor break, undercarriage and main wheel brakes

Question 77

fully explain the operation of the undercarriage system and the indication from the time the aircraft takes off and the undercarriage is fully retracted

Answer 77

3 green indicator light on the undercarriage control panel and repeater lights illuminate while on the ground and after take off to show wheels are down and locked when airborne WOW switch activates to energise the undercarriage control handle solenoid and remove the control handle lock when the undercarriage is selected up, (if stearing is centred) the control valve up solenoid will be energised and hydraulic pressure will be fed to remove the downlocks and retract the undercarriage red light illuminate to show wheels in transition when the undercarriage is up and locked the uplock microswitch will cause the uplock relay contacts to change over to lock in position all green and red light will extinguish and hydraulics are removed from the undercarriage

Question 78

explain the operation of the ECS cooling pack, explain the operation of the air cycle cooling machine

Answer 78

hot high pressure bleed air from the engine compressor is fed through the PRSOV (1) and the FCSOV(6) to the primary heat exchanger (7b) which reduces the tempurature the air is fed through the compressor (C) which raise the temperature and pressure of the air and feeds it to through the secondary heat exchanger (7c) where it is removed the air is then used to drive the turbine (T) which release the energy of the air allowing it to expand and reduce it temperature. at this temp, moisture in the air is removed by water seperator (7e) the turbine drives the compressor and the fan which are all on the same shaft. the fan draws external ambient air through the heat exchangers and vents it out. water collected by the water separator (7e) is injected into the heat exchanger to improve cooling efficiency