questions

Question 1

CS25 mandates aircraft must be able to fly and land safely after what 2 events in relations to the flying controls?

Answer 1

• a jam

- a severance

Question 2

how are control systems arranged to allow for jamming and severance?

Answer 2

• duplicated
• interconnected
• routed separately

Question 3

if a control system becomes jammed what two methods enable disconnection of the two parts of the system?

Answer 3

• manual disconnection by the pilot or first officer

- disconnection by the disconnect unit separating if a predetermined force is exceeded

Question 4

how is differential aileron movement achieved?

Answer 4

the bell crank on the down side is positioned below the horizontal so an equal angular movement creates a smaller linear movement

Question 5

how many switches need to be pressed to operate a typical electrical aileron trim system, what are they called and what do they do?

Answer 5

• two switches
• arm and command
• arm powers up the system, command supplies and moves the actuator

Question 6

how does the roll disconnect unit work and and when can it be reset?

Answer 6

• a predetermined force overcomes a spring
• disconnects left and right ailerons in event of jam
• provides indication on flight deck but can only be reset on ground

Question 7

what type of motor is used to operate the autopilot servo?

Answer 7

• a reversible motor

- or a split field motor

Question 8

briefly describe how a gust damper works

Answer 8

• damper attached at rear spar and at flying control

- movement of fluid from one side of actuator piston to the other restricted so slows movement of flying control

Question 9

where are the primary and secondary stops in a control rod system?

Answer 9

primary stops on the control column, secondary stops on the control surface

Question 10

briefly describe the operation of a solenoid brake

Answer 10

• electrical power releases brake held on by spring
• this enables motor to rotate and move flying control system
• when electrical power is removed, spring applies brake and system is locked in required position, providing irreversibility

Question 11

list 2 advantages and 2 disadvantages of a control rod system over a cable operated system

Answer 11

• control rods more robust and do not suffer differential expansion issues
• control rods heavier and more difficult to route

Question 12

what speed does the stall warming operate at?

Answer 12

5% above stall speed for that configuration and phase of flight

Question 13

if the stall protection operates what happens when the aircraft reaches a safe speed?

Answer 13

the stick pusher/nudger is disengaged and the control return to neutral at a safe speed

Question 14

in a power assisted system, what happens to the pilots input?

Answer 14

it is amplified by a hydraulic actuator

Question 15

in a power assisted system, what ‘nulls’ the servo valve?

Answer 15

the movement of the actuator body provides negative feedback and nulls the servo valve input by covering the hydraulic transfer ports

long answer: the pilot’s input moves a servo valve, which directs hydraulic pressure to one side or another of a piston which is anchored to the aircraft structure. this moves the actuator body providing negative feedback and nulling the pilots input

Question 16

in addition to being safe, positive and instinctive, powered flying control systems must also provide… (5)

Answer 16

• sensitivity
• stability
• irreversibility
• feedback
• redundancy

Question 17

what is meant by a control surface being irreversible?

Answer 17

once positioned, the aerodynamic forces acting on it cannot move it, it stays where it is until it receives an input to move

Question 18

what does the interconnecting valve do and when?

Answer 18

connects both sides of the cylinder to prevent a hydraulic lock when system pressure fails

Question 19

what five things does the servo valve control?

Answer 19

• size
• magnitude
• speed
• direction
• rate of movement
  of the actuator

Question 20

how does a stuck valve detector strut operate and what does it operate?

Answer 20

• in event of stuck servo valve, the strut ‘breaks’
• this allows other control inputs to keep operating in compression or tension
• this operates a microswitch which informs the pilot and operates the hydraulic clutch to isolate the hydraulics to the stuck servo valve

Question 21

what should the maximum freeplay on a trim tab not exceed?

Answer 21

2.5% of the average chord length of the tab

Question 22

in addition to the speed, attitude and altitude of the aircraft, list two other factors the stall warning system considers?

Answer 22

• position of high lift devices
• undercarriage position
• possibly altitude

Question 23

what does the transfer valve do?

Answer 23

• turns electrical inputs from autopilot into proportional hydraulic flow via flexible pipe
• to direct pressure to operate the input linkage to the servo valve to operate the PCU

Question 24

describe a tandem hydraulic actuator

Answer 24

• two separate hydraulic inputs
• two pistons
• two servos
• one cylinder

Question 25

what is the simplest form of artificial feel device?

Answer 25

a spring

Question 26

briefly describe a Q feel system that does NOT use hydraulics

Answer 26

• pitot and static pressures are on either side of a diaphragm and the diaphragm is connected to the control run
• as the pilot moves the stick he does so against the resistance of the diaphragm to move which is proportional to static and pitot pressure

Question 27

what should a Q feel system do when the pilot releases the control column?

Answer 27

return the control column to neutral

Question 28

name four ways to operate a hydraulic pump to pressurise an aircraft system in normal and emergency conditions

Answer 28

• engine driven
• electrical
• ram air turbine
• reversible motor

Question 29

on a variable incidence stabiliser, list five inputs to the elevators

Answer 29

• neutral shift rod
• pilots input
• autopilot
• mach trim
• trim

Question 30

what is neutral shift?

Answer 30

ensuring the elevator remains streamlined to the stabiliser when it moves

Question 31

what are the conditions to extend the speedbrakes on a rejected take off (RTO)?

Answer 31

• throttles at idle
• thrust reverse selected
• wheel rotation

Question 32

in a typical fly by wire system, if there are two PCU’s on a elevator and one is active and the other idling, what will make the other active?

Answer 32

if the active actuator fails or stalls under load

Question 33

list four advantages of a FBW control system over a mechanical control system

Answer 33

• lighter
• less maintenance
• more economical
• better manoeuvre protection
• gust load alleviation

Question 34

what three types of loads on the wings does active load control deal with?

Answer 34

• aero elastic loads (when gusts are encountered)
• manoeuvring loads (reduce wing bending)
• high lift loads (reduce wing bending under conditions of high lift, ailerons are raised a few degrees when the flaps are not fully up and the speed less than a specific value)

Question 35

what would you use to carry out a static friction check on an aileron control system and what part of the system might have to be disconnected to get a true reading?

Answer 35

a spring balance and disconnect any feel springs

Question 36

in ah hydraulically operated flap system, what does the bypass valve do if there is an asymmetry?

Answer 36

operates to remove the hydraulic lock so the alternate system can operate

Question 37

what value will a torque limiter operate at?

Answer 37

system torque+ 20%

Question 38

describe briefly the operation of the auto slat system

Answer 38

• slats deploy as part of the stall protection system depending on speed, AOA, config etc
• retract when the forward speed is at a safe level