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
- A/P or A/THR
• Manual
- Pilot activates as side sticks or thrust levers
- 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
- 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
The Auto Flight System (AFS) is divided into four main parts:
- Flight Management (FM),
- Flight Guidance (FG),
- Flight Augmentation,
- 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,
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.
- 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
Navigation database
- Provides necessary information for flight plan construction and follow up
- Database updated every 28 days
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
|
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
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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