AUTOMATIC FLIGHT SYSTEM DESIGN PHILOSOPHY
AUTOPILOT PRESENTATION
GENERAL
The AP is engaged from the Flight Control Unit (FCU) by the related
pushbuttons. AP engagement is indicated by the illumination of the AP
1 P/BSW or/and the AP 2 P/BSW (Three green bars) and by the white
"AP1", "AP2" or "AP1+ 2" indication on the top right corner of each
PFD. The AP guidance modes are selected from the FCU or the Flight
Management and Guidance Computers (FMGCs). The AP function is a
loop where, after a comparison between real and reference parameters,
the FMGC computes orders, which are sent to the flight controls. The
loop is closed by real values coming from sensors and given by other
systems (e.g. ADIRS) to the FMGCs. When the AP is engaged, the load
thresholds on the rudder pedals and the side sticks are increased. If a
pedal or side stick load threshold is overridden, the AP disengages.
MODES
There are lateral modes and vertical modes. Basically, one of each is
chosen by the pilot or by the system. The AP being engaged, one lateral
mode and one vertical mode are simultaneously active.
According to flight phases, the lateral mode controls:
- the ailerons via the ELevator Aileron Computers (ELACs),
- the spoilers via the ELACs and the Spoiler Elevator Computers (SECs),
- the rudder via the Flight Augmentation Computers (FACs),
- the nose wheel via the ELACs and the Braking/Steering Control Unit
(BSCU).
The vertical mode controls the elevators and the THS via the ELACs.
GROUND
For maintenance purposes, the AP can be engaged on ground with both
engines shut down. Hydraulic power is not required.
When an engine is started, the AP disengages.
TAKE-OFF
The AP can be engaged in flight, provided the aircraft has been airborne
for at least 5 seconds.
CRUISE
In cruise, only one AP can be engaged at a time, priority given to the last
engaged. Engaging the second AP disengages the first one. The ailerons
and the spoilers execute the orders of lateral modes; the elevators and
the THS execute the orders of vertical modes.
NOTE: The rudder is controlled not by the AP but directly by the FACs.
LANDING
If the airfield is equipped with ILS installations, the AP can perform a
complete landing with approach, flare and roll out. A second AP can be
engaged (AP 1 active, AP 2 in standby).
NOTE: The rudder is controlled by the AP via the FACs.
During roll out, the AP gives steering orders to the rudder and the nose
wheel. These orders depend on the aircraft speed. Aileron and spoiler
AP orders are null. The THS is reset to 0.5 nose up.
NOTE: The spoilers are directly controlled by the SECs as airbrakes.
During roll out, at low speed (about 60 knots), the pilot normally
disengages the AP by pressing a takeover pushbutton located on the side
stick.
FLIGHT DIRECTOR PRESENTATION
ENGAGEMENT
The Flight Director (FD) functions are engaged automatically as soon as
the system is electrically supplied and logic conditions are fulfilled.
FD engagement is indicated on the Flight Control Unit (FCU) by the FD
P/BSW green bars and on the top right of each PFD. 1FD2 indication is
displayed on each PFD to show that FD1 is engaged on the CAPT side
and FD2 is engaged on the F/O side.
NOTE: On ground, as long as no AP/FD mode is active, there are no
FD symbols on the PFDs.
PRINCIPLE
The FD displays the Flight Management and Guidance Computer (FMGC)
guidance commands on both PFDs. In manual flight, the FD displays
guidance orders to help the pilots to apply commands on the controls in
order to follow the optimum flight path, which would be ordered by the
AP if it was engaged. When the AP is engaged, the FD helps the FMGC
demands to be checked.
The FD modes are the same as the AP modes and are selected the same
way. The FMGCs calculate AP/FD orders which are transformed into
symbols by the Display Management Computers (DMCs). There are two
types of symbols: the FD bars, the Flight Path Director (FPD) and Flight
Path Vector (FPV) symbols. The central HeaDinG-Vertical Speed
(HDG-V/S)/TRacK-Flight Path Angle (TRK-FPA) P/BSW on the FCU
makes the pilots switch between these two types of symbols.
FD PUSHBUTTONS
Upon FCU power up, in go around, or when losing the AP during the
roll out phase of the landing, the three green bars of the FD P/BSWs
come on automatically. A lit FD P/BSW means that the FD symbols can
be displayed on the corresponding PFD: PFD 1 for the CAPT FD P/BSWand PFD 2 for the F/O FD P/BSW. If a lit FD P/BSW is pressed, the
green bars go off. Pressing the P/BSW again puts the green bars on again.
A non lit FD P/BSW means that no FD symbols can be displayed on the
corresponding PFD. -FD2 is displayed on each PFD to show that no FD
symbols can be displayed on PFD 1 and FD 2 is engaged on the F/O side.
FD BARS
The FD bars can be displayed provided HDG-V/S is selected on the FCU.
HDG-V/S is automatically selected at system power up.
NOTE: At certain system configuration changes, the FMGCs send a
command to the DMCs to make the FD bars flash for 10
seconds.
AP/FD modes are correctly followed when the FD bars are centered on
the fixed aircraft model of the PFDs.
There are three FD bars:
- the pitch bar,
- the roll bar,
- and the yaw bar.
The horizontal pitch bar can be displayed if a vertical mode is active
except during the roll out phase of the landing. The vertical roll bar can
be displayed if a lateral mode is active. Below 30 feet RA at take-off
when a LOCalizer (LOC) signal is available and during landing, the roll
bar is replaced by a yaw bar index. This bar is then centered when it is
just below the central yellow square.
FPD/FPV SYMBOLS
The FPD and the FPV symbols can be displayed provided TRK-FPA is
selected on the FCU.
NOTE: At certain system configuration changes, the FMGCs send a
command to the DMCs to make the FPD and FPV symbols
flash for 10 seconds.
AP/FD modes are correctly followed when the FPD and FPV symbols
are superimposed. The FPD symbol supplies command signals to intercept
and fly the lateral and vertical flight path as defined by the FMGCs. The
FPD symbol is removed if no guidance mode is provided by the FMGCs.
The FPV symbol represents lateral and vertical flight path informationin terms of current track and FPA actually being flown. The FPV symbol
position is computed by the Air Data Inertial Reference System (ADIRS).
NOTE: The yaw bar is identical to the FD bar case and appears with
the same conditions.
AUTOTHRUST FUNCTION
The A/THR function sends a computed thrust command (thrust target)
to the Full Authority Digital Engine Control (FADEC) for automatic
engine control.
The A/THR functions are:
- acquisition and holding of a speed or a Mach number,
- acquisition and holding of a thrust,
- reduction of the thrust to idle during descent and during flare in final
approach,
- protection against excessive Angle-Of-Attack (AOA) called alpha-floor
protection, by ordering a maximum thrust when an alpha-floor detection
signal is received from the Flight Augmentation Computers (FACs).
AUTOTHRUST LOOP PRINCIPLE
To get the A/THR function, the thrust target computed by the Flight
Management and Guidance Computers (FMGCs) is chosen by the Flight
Control Unit (FCU). Then each FCU processor sends, along its own bus,
the thrust target to the FADEC via the Engine Interface Units (EIUs).
AUTOTHRUST ENGAGEMENT
The engagement of the A/THR function can be manual or automatic. The
A/THR is engaged manually by pressing the A/THR P/BSW on the FCU.
This is inhibited below 100 feet RA, with engines running.
The A/THR is engaged automatically:
- when the AP/Flight Director (FD) is engaged in Take-Off (TO) or Go
Around (GA) modes,
- or in flight, when the alpha-floor is detected; this is inhibited below 100
feet RA except during the 15 seconds following the lift-off.
NOTE: To effectively have A/THR on the engines, the engagement of
the A/THR is confirmed by a logic of activation in the FADEC.
When A/THR is engaged:
- the FCU A/THR P/BSW is lit,
- the engagement status is displayed on the Flight Mode Annunciator
(FMA).
When engaged, the A/THR can be active or not depending on the position
of the thrust levers. When engaged and not active, the thrust control is
manual. The thrust is commanded according to the position of the thrust
levers. When engaged and active, the thrust control is automatic. The
thrust is commanded according to the A/THR computed thrust target.
AUTOTHRUST DISCONNECTION
A/THR disengagement can be manual or automatic.
A/THR is manually disconnected:
- either by pressing the A/THR instinctive disconnect switch on any thrust
lever,
- or by setting all thrust levers to idle position,
- or through the dedicated FCU P/BSW,
A/THR is automatically disconnected in case of failure detection.
Tags:
AUTOMATIC FLIGHT SYSTEM