M11.9

Question 1

What are common types of trim systems?

Answer 1

Trim tabs; Servo tabs; Balance tabs; Spring tabs; Anti‑balance/anti‑servo

Question 2

How do modern aircraft control and trim flight surfaces?

Answer 2

Using electrical or hydraulic systems that move the main control surfaces; includes Mach Trim for high‑speed compensation.

Question 3

What are typical trim input sources?

Answer 3

Pilot controls via wheels/switches/knobs; Autopilot and sensors sent to FCUs.

Question 4

How is the horizontal stabiliser typically trimmed?

Answer 4

By an electrically commanded, hydraulically driven screwjack with position shown on EICAS/ECAM.

Question 5

How is lateral trim controlled?

Answer 5

By a centre‑console switch; electrically through the FCU to a servo; moves the control wheel and displays on EICAS.

Question 6

How is yaw trim controlled?

Answer 6

By a rotary knob on the centre console; purely electrical through FCU to servo.

Question 7

How can pilots manually control longitudinal stabiliser trim?

Answer 7

Using pitch trim switches on each control wheel sending signals to ACEs, or mechanical trim levers on the captain’s side.

Question 8

What is the purpose of stabiliser trim cut‑out switches?

Answer 8

To shut off hydraulic pressure to the Stabiliser Trim Control Modules (STCMs).

Question 9

What do stabiliser position indicators show?

Answer 9

Stabiliser angle and the green band for correct take‑off setting.

Question 10

Why is active load alleviation needed?

Answer 10

Light, flexible wings deform under aerodynamic loads, affecting performance; control systems counteract these effects.

Question 11

What are the two main types of active load alleviation?

Answer 11

Manoeuvre Load Control (MLC) and Gust Load Alleviation (GLA).

Question 12

What does Manoeuvre Load Control (MLC) do?

Answer 12

Uses ailerons/spoilers to move lift inboard and reduce wing‑root bending moment.

Question 13

What does the Gust Load Alleviation System do?

Answer 13

Uses sensors to detect gusts and deflects control surfaces to reduce gust‑induced loads and maintain ride comfort.

Question 14

Why are ailerons effective for GLA?

Answer 14

Their outer‑wing location strongly affects bending moments but minimally affects total lift.

Question 15

What is the purpose of trailing edge flaps?

Answer 15

Increase camber to provide more lift at slow speeds; allow slower landing and shorter takeoff/landing distance.

Question 16

What are common types of trailing edge flaps?

Answer 16

Plain, Split, Slotted, Fowler, Fowler‑slotted flaps.

Question 17

What is the purpose of leading edge flaps?

Answer 17

Increase wing camber and lift, used with trailing edge flaps; retract into leading edge.

Question 18

What are types of leading edge devices?

Answer 18

Fixed slots; Moveable slots; Slats; Leading edge cuffs; Krueger flaps.

Question 19

What do lift dump spoilers do?

Answer 19

Assist roll control and provide speed‑brake function to reduce lift and increase drag.

Question 20

What are speed brakes?

Answer 20

Secondary flight controls that increase drag to reduce aircraft speed; may deploy automatically on ground.

Question 21

What do manually operated flight control systems use?

Answer 21

Mechanical components: cables, pulleys, bell cranks, push‑pull tubes.

Question 22

Why are manual systems common in small aircraft?

Answer 22

Aerodynamic forces are low enough for mechanical control.

Question 23

What are gust locks?

Answer 23

Devices to lock control surfaces on the ground to prevent wind damage.

Question 24

What are typical aircraft control cables?

Answer 24

7×7 or 7×19 steel wire ropes handling high tensile loads.

Question 25

Why are control cables arranged in loops?

Answer 25

Because they pull only; loops enable two‑way movement.

Question 26

What do fairleads do?

Answer 26

Guide, align, reduce vibration, prevent wear, and seal bulkhead openings.

Question 27

What is the purpose of cable seals?

Answer 27

Prevent pressurisation loss between cabin and unpressurised sections.

Question 28

What does a tensiometer measure?

Answer 28

Cable tension by measuring deflection force.

Question 29

Why must cable tension be temperature‑corrected?

Answer 29

Temperature affects tension; rigging charts provide correction.

Question 30

What do tension regulators do?

Answer 30

Automatically maintain proper cable tension as structures expand/contract.

Question 31

How do tension regulators work?

Answer 31

Springs extend/compress to keep equal tension both sides.

Question 32

What is a push‑pull rod?

Answer 32

A rod transferring forces in both tension and compression.

Question 33

What are witness holes for?

Answer 33

To confirm thread engagement in adjustable rods.

Question 34

What do bell cranks do?

Answer 34

Change direction of movement and transfer control input.

Question 35

What are torque tubes for?

Answer 35

Transmit torsional motion to control surfaces, often using splines and universal joints.

Question 36

What is a screw jack?

Answer 36

A threaded device converting rotary motion to linear movement for high‑load surfaces.

Question 37

Why were hydraulic control systems developed?

Answer 37

Larger/faster aircraft needed assistance due to high aerodynamic loads.

Question 38

What is a hydraulic Power Control Unit (PCU)?

Answer 38

Assembly combining hydraulic components to position and structurally support control surfaces.

Question 39

What is in a servo control unit?

Answer 39

Power section (piston/cylinder) + distribution section (control valve + bypass valve).

Question 40

Active control mode function?

Answer 40

Hydraulic pressure moves actuator based on valve input.

Question 41

Damping mode function?

Answer 41

Depressurised PCU provides gust damping only.

Question 42

What is reversible power‑assisted control?

Answer 42

Hydraulic assistance but manual control still possible after hydraulic failure.

Question 43

What is fully powered (irreversible) control?

Answer 43

Pilot has no direct link; artificial feel required.

Question 44

Why are pneumatic systems limited?

Answer 44

Air is compressible; suitable mainly for backups or leading‑edge flap systems.

Question 45

What is an Electrical PCU?

Answer 45

PCU with electronically controlled servo valve (EHSV).

Question 46

Normal mode of electrical PCU?

Answer 46

ACE energises solenoids; EHSV controls actuator with LVDT feedback.

Question 47

Bypass mode of electrical PCU?

Answer 47

Hydraulic pressure isolated; adjacent PCU back‑drives actuator.

Question 48

Blocked/damped mode of electrical PCU?

Answer 48

Both solenoids off; actuator cannot extend, only slow retraction.

Question 49

What is fly‑by‑wire (FBW)?

Answer 49

Electronic interface replacing mechanical linkages to command control surfaces.

Question 50

What does FBW stability use?

Answer 50

Gyros sensing pitch/roll/yaw, computers move actuators without moving cockpit controls.

Question 51

What are control laws?

Answer 51

Software defining how pilot inputs become surface movements.

Question 52

What is normal law?

Answer 52

Full flight envelope protection with phase‑dependent behaviour.

Question 53

What is alternate law?

Answer 53

Reduced protections; may degrade to direct or mechanical law.

Question 54

What is fly‑by‑wireless?

Answer 54

Wireless signal networks reducing wiring weight and maintenance.

Question 55

What is artificial feel?

Answer 55

Mechanical/hydraulic systems simulating aerodynamic resistance.

Question 56

What is a Q‑pot feel system?

Answer 56

Uses pitot pressure + hydraulics to give airspeed‑proportional feel.

Question 57

What is a yaw damper?

Answer 57

System applying automatic rudder to suppress Dutch Roll.

Question 58

What is Mach trim?

Answer 58

Automatic nose‑up trim to counter Mach tuck in transonic flight.

Question 59

Why is a rudder limiter needed?

Answer 59

Limits rudder travel at high speeds to prevent structural overload.

Question 60

What is aircraft balancing?

Answer 60

Ensuring control surfaces are statically/dynamically balanced for safe handling.

Question 61

Static balance definitions?

Answer 61

Underbalance (+): TE drops. Overbalance (–): TE rises.

Question 62

What is rebalancing?

Answer 62

Adjusting counterweights after repairs/painting to restore proper balance.

Question 63

What is aircraft rigging?

Answer 63

Adjusting control systems for correct travel, tension, and alignment.

Question 64

Steps to check flight control movement?

Answer 64

Lock controls neutral → adjust tension → set stops → confirm full movement.

Question 65

What do manually operated flight control systems use?

Answer 65

Mechanical components: cables, pulleys, bell cranks, push‑pull tubes.

Question 66

Why are manual systems common in small aircraft?

Answer 66

Aerodynamic forces are low enough for mechanical control.

Question 67

What are gust locks?

Answer 67

Devices to lock control surfaces on the ground to prevent wind damage.

Question 68

What are typical aircraft control cables?

Answer 68

7×7 or 7×19 steel wire ropes handling high tensile loads.