This document provides an overview of flight control systems, engine control systems, and environmental control systems on aircraft. It discusses primary and secondary flight controls, control linkage systems using rods or cables, and flight control actuation methods ranging from mechanical to fly-by-wire systems. It also covers engine technology, fuel and air flow control, bleed air systems, and engine control parameters and examples of control systems. Finally, it discusses hydraulic system design and components, environmental control needs like cooling and pressurization, and methods for cabin temperature control and humidity control.

1. Module 1
Flight Control Systems

2. Primary and Secondary Flight Control

4. Flight Control Linkage Systems
The pilot’s manual inputs to the flight controls are made by moving the cockpit
control column or rudder pedals in accordance with the universal convention:
• Pitch control is exercised by moving the control column fore and aft; pushing
the column forward causes the aircraft to pitch down, and pulling the column
aft results in a pitch up
• Roll control is achieved by moving the control column from side to side or
rotating the control yoke; pushing the stick to the right drops the right wing
and vice versa
• Yaw is controlled by the rudder pedals; pushing the left pedal will yaw the
aircraft to the left while pushing the right pedal will have the reverse effect
There are presently two main methods of connecting the pilot’s controls to the
rest of the flight control system. These are:
• Push-pull control rod systems
• Cable and pulley systems

7. Cable and Pulley System

9. High Lift Control Systems

11. Flight Control Actuation
The key element in the flight control system, increasingly so with the advent
of fly-by-wire and active control units, is the power actuation. Actuation has
always been important to the ability of the flight control system to attain
its specified performance. The development of analogue and digital multiple
control lane technology has put the actuation central to performance and
integrity issues. Addressing actuation in ascending order of complexity leads
to the following categories:
• Simple mechanical actuation, hydraulically powered
• Mechanical actuation with simple electromechanical features
• Multiple redundant electromechanical actuation with analogue control
inputs and feedback
The examination of these crudely defined categories leads more deeply into
systems integration areas where boundaries between mechanical, electronic,
systems and software engineering become progressively blurred.

12. Conventional Linear Actuator
Blue channel
Green channel
Hydaulic power
Mechanical Signalling Summing link
Hydraulic
piston
actuator
Feedback link
SV SV

13. Mechanical Screwjack Actuator

14. Advanced Actuation Implementations
The actuation implementations described so far have all been mechanical or
electro-hydraulic in function using servo valves. There are a number of recent
developments that may supplant the existing electro-hydraulic actuator. These
newer types of actuation are listed below and have found application in aircraft
over the past 10–15 years:
Direct Drive Actuation
Fly-by-Wire (FBW) actuation
Electro-Hydrostatic Actuator (EHA)
Electro-Mechanical Actuator (EMA

15. Direct Drive Actuation
In the electro-hydraulic actuator a servo valve requires a relatively small elec-
trical drive signal, typically in the order of 10–15 mA. The reason such low
drive currents are possible is that the control signal is effectively amplified
within the hydraulic section of the actuator. In the direct drive actuator the
aim is to use an electrical drive with sufficient power to obviate the need for
the servo valve/1st stage valve. The main power spool is directly driven by
torque motors requiring a higher signal current, hence the term ‘direct drive’.
Development work relating to the direct drive concept including comparison
with Tornado requirements and operation with 8 000psi hydraulic systems
has been investigated by Fairey Hydraulics see reference [9]. This paper also
addresses the direct digital control of aircraft flight control actuators.

16. Fly-By-Wire Actuator

17. Electro-Hydrostatic Actuator (EHA)

18. Electro-Mechanical Actuator (EMA)

19. Module 2
Engine Control Systems

20. Engine Technology and Principles of
Operation
Illustrations of single
and multiple spool
engines

21. Two and three shaft
turbofans

22. Fuel Flow Control

23. Air Flow Control
Engine air
management

24. Bleed air control – RR Trent 800 example

25. Control Systems
The number of variables that affect engine performance is high and the nature of the
variables is dynamic, so that the pilot cannot be expected constantly to adjust the
throttle lever to compensate for changes, particularly in multi-engined aircraft. In the
first gas turbine engined aircraft, however, the pilot was expected to do just that.
A throttle movement causes a change in the fuel flow to the combustion chamber spray
nozzles. This, in turn, causes a change in engine speed and in exhaust gas temperature.
Both of these parameters are measured; engine speed by means of a gearbox mounted
speed probe and Exhaust Gas Temperature (EGT), or Turbine Gas Temperature (TGT), by
means of thermocouples, and
presented to the pilot as analogue readings on cockpit-mounted indicators. The pilot can
monitor the readings and move the throttle to adjust the conditions to suit his own
requirements or to meet the maximum settings recommended by the engine
manufacturer. The FCU, with its internal capsules, looks after variations due to
atmospheric changes.
In the dynamic conditions of an aircraft in flight at different altitudes, temperatures and
speeds, continual adjustment by the pilot soon becomes impractical. He cannot be
expected continuously to monitor the engine conditions safely for a flight of any
significant duration. For this reason some form of automatic control is essential.

26. Control System Parameters
Engine control
systems – basic
inputs and
outputs

27. 5 Input Signals
• Throttle position
• Air data – Airspeed and altitude
• Total temperature
• Engine speed
• Engine temperature
• Nozzle position
• Fuel flow
• Pressure ratio

28. 6 Output Signals
• Fuel flow control
• Air flow control

29. Example Systems
A simple engine
control system –
pilot in the loop

30. A simple limited authority engine control system

31. Engine control system with NH and TGT exceedence warnings

32. Full authority engine control system with electrical throttle signalling

33. The RB199 control system in the BAE Systems EAP

34. A modern simplified engine control system

35. Turbojet Engine (EJ200 in Eurofighter Typhoon)

36. Turbofan (Trent 1000 in Boeing B787) Turboprop (EPI TP400 in A400M)

37. Helicopter (T800 in EH101 & NH-90)

38. Engine Starting
To start the engines a sequence of events is required to
allow fuel flow, to rotate
the engine and to provide ignition energy. For a particular
type of aircraft this
sequence is unvarying, and can be performed manually
with the pilot referring
to a manual to ensure correct operation, or automatically
by the engine control
unit. Before describing a typical sequence of events, an
explanation of some of
the controls will be given.

39. Fuel Control
Typical location of LP and HP Cocks

40. Ignition Control
Engine ignition

41. Engine Rotation
APU functional diagram
APU – airborne
rating example

42. Throttle Levers
The throttle lever assembly is often designed to incorporate HP cock switches
so that the pilot has instinctive control of the fuel supply to the engine.
Microswitches are located in the throttle box so that the throttle levers
actuate
the switches to shut the valves when the levers are at their aft end of travel.
Pushing the levers forward automatically operates the switches to open the
fuel cocks, which remain open during the normal operating range of the
levers.
Two distinct actions are required to actuate the switches again. The throttle
lever must be pulled back to its aft position and a mechanical latch operated
to allow the lever to travel further and shut off the fuel valve.

43. Starting Sequence
A typical start sequence is:
Open LP cocks
Rotate engine
Supply ignition energy
Set throttle levers to idle – open HP cocks
When self-sustaining – switch off ignition
Switch off or disconnect rotation power source
Together with status and warning lights to indicate ‘start in progress’, ‘failed
start’ and ‘engine fire’ the pilot is provided with information on indicators
of engine speeds, temperatures and pressures that he can use to monitor the
engine start cycle.
In many modern aircraft the start cycle is automated so that the pilot has only
to select START for the complete sequence to be conducted with no further
intervention. This may be performed by an aircraft system such as Vehicle
Management, or by the FADEC control unit. In future this sequence may be
initiated by an automated pre-flight check list.

44. Engine Indications
Engine speed – NH and NL
Engine temperature
Pressure ratio
Engine vibration
Thrust (or torque)

45. Some examples of engine synoptic displays

46. Engine Oil Systems

47. Module 3
Hydraulic and Environment Control Systems

48. Hydraulic Circuit Design
Hydraulic system loads

49. • Pressure
• Integrity
• Flow rate
• Duty cycle
• Emergency or reversionary use
• Heat load and dissipation

50. A simple hydraulic system

51. Hydraulic Actuation

52. Hydraulic Fluid
The working fluid will be considered as a physical medium for transmitting
power, and the conditions under which it is expected to work, for example
maximum temperature and maximum flow rate are described.
Safety regulations bring about some differences between military and civil
aircraft fluids. With very few exceptions modern military aircraft have, until
recently, operated exclusively on a mineral based fluid known variously as:
DTD 585 in the UK
MIL-H-5606 in the USA
AIR 320 in France
H 515 NATO

53. Fluid Pressure
Fluid Temperature
Fluid Flow Rate
Hydraulic Piping

54. Hydraulic Pumps
Characteristic curve for a ‘constant pressure’ pump

55. Examples of hydraulic pump
technology

56. Working principle of a piston pump

57. Need for a Controlled Environment

58. Ram Air Cooling

59. Fuel Cooling

60. Engine Bleed
Use of fuel as a coolant for hydraulic or engine oil

61. Closed loop cooling system

62. Bleed Flow and Temperature Control
Mixing hot air with heat exchanger outlet

63. Cabin temperature control system

64. Air Cycle Refrigeration
• Humidity Control
• Hypoxia

65. Tolerance