A320 Auto Flight System Notes

ATA 22 Auto Flight

• Auto flight systems (AFS) calculates orders to automatically control flight controls (EFCS) and engines(FADEC)
• AFS is built around 4 computers,  two interchangeable Flight Management and Guidance Computers (FMGCs) and two interchangeable Flight Augmentation Computers (FACs). Each  consist of command and monitor channel.
• It is a FAIL OPERATIVE system.

Basic operational principles

 In normal operations

               • Automatic
                        - A/P or A/THR

    • Manual
            - Pilot activates as side sticks or thrust levers

Navigation principles:

• Calculated position of the A/C using several sensors
  • Inertial system
  • Radio navigation system
• Flight plan
  • Stored in the memory predetermined by the operator
  • Describe complete flight from T/O to landing
  • Vertical information
  • Intermediate way points

Operation:

Normal way

            • AFS uses flight plan automatically
                - Position and desired flight plan (chosen by crew), system will computed     orders then send to the surfaces and engines to follow the flight plan
                - During AFS side stick and throttle levers will not move

AFS fly by wire

            • When A/P system engaged, apply force on the side stick causes A/P disengage, after normalize the force on the side stick A/C will maintain actual attitude with manual flight

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The Auto Flight System (AFS) is divided into four main parts:

1. Flight Management (FM),
2. Flight Guidance (FG),
3.  Flight Augmentation,
4.  Fault Isolation and Detection System (FIDS).

1. FM (Flight Management )

- It can be made by different manufacturer than the FG part, and can be replaced separately

- Controlled/interfaced from the MCDU

Its responsible for:

• Flight planning
• Lateral Navigation
• Vertical Navigation

2. FG (Flight Guidance)

- Consist of 2 parts Command and Monitoring

           - Controlled/interfaced from FCU

    Its responsible for:

•  AP
• FD
• A/THR

3. Flight Augmentation

The basic functions of the Flight Augmentation Computer (FAC) are:
    a) yaw damper,
    b) rudder trim,
    c) rudder travel limitation,
    d)flight envelope protection,

- Fault Isolation and Detection System (FIDS).

a) The yaw damper provides:
        - dutch roll damping,
        - turn coordination in cruise,
        - engine failure compensation in auto flight,
        - yaw guidance order execution.

b) Rudder Trim

• Manual trim from the Rudder trim control panel
• Auto trim
•  Through FMGC via FAC to rudder trim actuator with A/P engaged

c)  Rudder Travel Limitation

• Limits rudder travel according to the A/C speed for structure Integrity (Speed information comes from ADIRUs)
• Prevents excessive deflection which penalize the A/C performance

d) Flight Envelope Protection:

• Speed
• AOA
• Wind Shear

4. FIDS (Fault Isolation and Detection System)

• Used as a system Bite to concentrate maintenance information and compare with all information from
  other AFS computers to filter unwanted gives most accurate faults to CFDS
• Receives commands from CFDS and sent to other AFS system Bites and receives malfunction report from
  Bites if applicable reports to CFDS
• If FIDS fails Bites continues to work and the result can be read in the shop or after FAC 1 change 

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Navigation database

• Provides necessary information for flight plan construction and follow up
• Database updated every 28 days

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AP and FD modes

Guidance	Managed modes	Selected modes
LATERAL	NAV, APP NAV LOC *, LOC RWY, RWY TRK GA TRK ROLL OUT	HDG - TRK
VERTICAL	SRS (T.O and G.A) CLB, DES ALT CST, ALT CST * ALT CRZ * , ALT CRZ G/S *, G/S FINAL, FINAL APP FLARE	OPCLB, OPDEC V/S, FPA ALT*, ALT EXPEDITE
SPEED	FMGC REFERENCE (ECON auto SPD LIM) Expedite	FCU REFERANCE

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A/P engagement

• Possible only 5 sec after lift off and only one at a time
• To select land mode allows both A/P to engage
• After T/O to rollout A/P remain engaged to control A/C on the runway center line
• A/P disengagement by pilot at low speed taxing
• On Gnd. can be engaged if engines are not running

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Flight Director

• Displays Guidance commands on both PFD to fly manually according to FMGC demand
• Two cases to be considered

• A/P not engaged

• F/D symbols display on PFD, gives orders to pilot to maintain the desired parameters
  (crew fly A/C as per the orders acting on flight controls)

• A/P Engaged

• FD function displayed symbol on PFD represent A/P orders to be monitored by pilots 

FD(Flight Directors)

Engaged:     

• with the Pushbutton at FCU
• During power Up(Automatic Engagement)
• During TCAS RA situation operation

Dis-engaged:

• with the Pushbutton at FCU
• When there is Failure

AP(Auto-Pilot)

Engaged:

• with the Pushbutton at FCU
• No Automatic Engagement

  Dis-engaged:

• with the Pushbutton at FCU
• Side Stick Disconnect switch
• Side stick Movement
• Not all conditions are met
• When there is Failure

A/THR(Auto-Thrust)

Engaged:

• with the Pushbutton at FCU
• When A/THR is moved to TO/GA
• During Alpha floor protection(Automatic Engagement)
• During TCAS RA situation operation

Disconnected:

• with the Pushbutton at FCU
• With the Pushbutton at the Thrust lever
• At IDLE power
•  When there is Failure

Some FAC functions:

• W/S Windshear
• Low Energy Warning (SPEED, SPEED, SPEED)
• ROPS(Runway Overrun prevention System)
• SRIW(Stop Radar Input)

• PWS(Predictive Windshear)

- Becomes active below 2300ft

- Visual warning becomes active below 1500ft: W/S AHEAD

- Aural warning becomes active below 1200ft: MONITOR RAD DISPLAY, WINDSHEAR       

  AHEAD  GO AROUND

Credit :    Rakesh Singh

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