First, a little general autoflight theory! The Airbus has
three “layers” or levels control if you wish to call it that. The first or
lowest level is manual control. This would be the pilot controlling through the
sidestick and the thrust levers.
|
Pilot |
|
|
Flight
Controls |
Thrust |
In this case the pilot is controlling any flight control
movement by use of the sidestick, which sends its signals through the
appropriate computers to the hydraulic actuators and finally the flight control
itself. The pilot can command any flight control movement that stays within
Flight Control Normal Law. The same holds true for thrust. The pilot can
manually control the thrust levers to command any thrust level that stays within
the normal engine operating parameters. This is hand flying as you have always
done. Do not confuse the flight control computers (i.e. ELAC, SEC and FAC) with
the flight management guidance computers (FMGC).
Level 2 –
“Manual with Flight Director”
|
Pilot |
|
|
Flight
Director |
|
|
Flight
Controls |
Thrust |
In this example the pilot maintains manual control of the
flight control but is being guided by the flight director. The flight director
(F/D) may be getting its cues from the FMGC or from the settings on the FCU.
The next level of control is autoflight. This is when the
autopilot and autothrust are engaged. In this case the pilot is controlling the
aircraft through the settings on the FCU for the autopilot and the thrust
levers. The pilot is telling the autopilot and autothrust directly what is
wanted. For example, if a heading of 90 is required the pilot just sets a
heading of 90 in the FCU and the autopilot holds that heading. If the pilot
wants a climb of 1000 fpm then the pilot sets 1000 fpm in the FCU.
|
Pilot |
|
|
Flight
Director |
|
|
Autopilot |
Autothrust |
|
Flight
Controls |
Thrust |
This level is basically the same as any other aircraft you
have flown with autopilot and autothrust. The autopilot and autothrust are
controlling through the same flight control system that the pilot uses when
hand flying.
The final and most sophisticated level is computer guided.
In this case the pilot enters the desired settings in the FMGC and the computer
calculates the proper flight path and track. The FMGC then commands the
autopilot and autothrust to properly maintain the computed track and path. If
the pilot wishes to make changes or revisions to the flight plan then it is
done to the FMGC which then recalculates the needed information. For example,
if the pilot wishes to change the flight plan route to go direct to a new fix,
the new fix is typed into the MCDU and entered into the DIR page. The FMGC now
computes the new course and commands the autopilot to turn to the new heading.
|
Pilot |
|
|
Flight
Director |
|
|
FMGC |
|
|
Autopilot |
Autothrust |
|
Flight
Controls |
Thrust |
Each higher level uses all the previous levels. In other
words computer guided flight is also using the autoflight and manual levels.
The pilot can always “drop down” from one level to a lower level by disengaging
the appropriate equipment. For example, the pilot may be climbing under
computer control in Managed Climb. By selecting a vertical speed of 1500 fpm on
the FCU the pilot has now put the vertical path in autopilot control. The FMGC
is not controlling the climb rate. If the pilot then disengages the autopilot
the aircraft is now under manual control and the pilot is now manually
controlling the climb rate.
Two things that should be pointed out. You can have various
levels of control at one time. For example, the track may be computer guided by
the FMGC while the vertical path is under autopilot control. Another example is
when the pilot is hand flying but using autothrust (which is very common). In
this case the flight controls are in manual but the thrust is in autoflight.
The other thing to point out is that when hand flying the pilot may use the
Flight Director so that while the aircraft is under manual control the pilot is
still getting autoflight or computer guided assistance.
Autopilot (PH
14.1.6)
There are two autopilots installed. Normally you will only
use one autopilot at a time (Capt. using A/P 1 and F/O using A/P 2). However,
for every ILS approach you will engage both autopilots (except, of course, when
the second is inop.).
iMake your flight instructor happy!: Use
Noun/Verb when commanding changes on the FCU (Flight Control Unit) (POH 18.1.3).
For Example:
“Speed Select 170” – pilot selects new speed of 170
“Speed Engage” – speed controlled by FMGC, known as managed
speed.
“Heading Select” – selects heading to previously dialed or
current heading “Heading Select 280” – pilot selects new heading of 280.
“Nav Engage” – track controlled by FMGC route
|
Autopilot |
“Autopilot
Off” or “Autopilot
1 (2)” |
|
Flight
Directors |
Flight
Directors Off or Flight
Directors On |
|
Speed |
“Speed
Select” or “Speed
Engage” |
|
Heading/Nav |
“Heading
Select” or “Nav
Engage” |
|
Open/Managed Climb
(Descent) |
“Open
Climb (Descent) Select” or “Climb (Descent) Engage” |
|
Vertical
Speed |
“Vertical
Speed Plus (Minus)” or “Altitude
Hold” |
Ø Select is
always knob pulled to you (pilot is “taking” the control of the autopilot).
When using select if you are changing the amount from what is in the window
then say amount after saying select.
The big picture on Airbus autothrust; During ground
operations handle the thrust levers as on a “normal” aircraft. At takeoff push
the thrust levers up to 50% on N1 until both engines stabilize, then push the
thrust levers up to FLX/MCT (two clicks) or TOGA (three clicks). When LVR CLB
flashes (normally about 1000’) on the FMA reduce the thrust lever back to CL
(one or two clicks). The thrust will now be controlled through the FMGC or the
FCU. The thrust levers in normal operation will not move again until landing
when at about 30 to 50’ the PF will reduce the thrust lever to idle and the
autothrust will automatically disconnect at that point. There is no physical
connection between the thrust levers and the powerplant. It is all done
electronically which is called FADEC (Full Authority Digital Engine Control).
Thrust is now set by selecting Open Climb (OP CLB) or Open
Descent (OP DES) or Managed climb or descent. Managed climb or descent means
that the FMGC is controlling in either. Open mode simply means using either
full climb thrust for climb or idle thrust for descent. Autothrust controls to
a limit in Open, either the climb limit or the idle limit.
The other “FCU”
method to control thrust is to set vertical speed (V/S) which allows the thrust
to maintain speed and climb rate is controlled through pitch. In this case
autothrust is maintaining speed and is in Speed mode. Of course, during cruise
and approach the altitude or glide slope is held through pitch with the
autothrust maintaining the required speed. Managed thrust is controlled by the
FMGC.
If you don’t get anything else out of this little discussion
please understand that the autothrust works in one of two modes, Open
(controlling thrust) and Speed (controlling speed). Further, Open mode can be
either climb or idle thrust.
Most of the time if you are going to have a problem it is in
the Open mode (controlling to thrust). If you are having problems with thrust
doing something other than what you think it should you can possibly try:
Ø Turn off
flight directors (if hand flying), this will cause autothrust to go to Speed
mode
Ø Select
vertical speed (if in Open climb or descent), this will cause autothrust to go
to Speed mode
Ø Select
Speed Select (if in Managed speed), this will force the commanded speed to what
you desire.
Arm A/THR (autothrust):
Arm on ground (with at least one FD on):
Ø Set thrust
lever in FLX/MCT if FLX temp is set
Ø Set thrust
lever to TOGA
Arm in flight:
Ø Press on
the A/THR pb on FCU when thrust levers not in active range or setting thrust
levers out of active range. Blue A/THR in FMA.
Activate
A/THR:
Note: on ground
you will set takeoff thrust to either FLX/MCT or TOGA which are manual thrust
settings. When coming back to the CL detent after takeoff you are putting the
thrust levers to the A/THR active range, thus activating autothrust.
Ø A/THR pb
pressed on when autothrust in active range
Ø Set thrust
levers to active range when A/THR pb armed
Ø ALPHA
FLOOR protection activated (not a great way to activate!)
Disconnect A/THR:
Ø Press
instinctive disconnect pb on thrust levers
Ø Place both
levers to idle detent
Ø Press off
the A/THR pb on FCU when system active (green light goes out)
Ø Set one
thrust lever beyond MCT or both beyond CL detent when RA is below 100’
Ø A FLOOR in
green with flashing amber box on FMA and in amber on E/WD
Ø TOGA LK in
green with a flashing amber box around it on the FMA when the A FLOOR condition
is left. TOGA thrust is frozen.
To cancel ALPHA FLOOR or TOGA LK disconnect the autothrust.
ALPHA FLOOR is available in NORMAL law only.
ALPHA FLOOR is enabled at liftoff and active during flight,
disabled at 100’ RA on approach to let you land the aircraft.
ALPHA FLOOR is disabled if you press the instinctive
disconnects for 15 secs.
Please note that Alpha Floor has
to do with autothrust while Alpha (α) Prot and Alpha (α) Max are
actually to do with flight controls.
THR LK – Thrust Lock occurs if the autothrust system fails.
THR LK flashes on the FMA and ECAM memo displays AUTO FLT A/THR OFF. The thrust
will be frozen at the last commanded setting until the pilot moves the thrust
levers, then thrust will follow the movement of the thrust levers and be
controlled manually.
iMake your flight instructor happy!: The
following is in bold print because it will make your life easier. Always match the TLA to the thrust before
disconnecting (using instinctive disconnect pb), no matter what kind of thrust
situation you are in. This works in normal autothrust, THRUST LOCK and TOGA
LOCK. Although not always technically necessary, by matching TLA to thrust you
always avoid any unintentional thrust “excursions” and use good practice. Think
“Match and Mash”.
During every approach you will need to confirm autothrust is
in SPEED mode on FMA or off by 1000’
Missing Link or AP/FD & A/THR interaction (PH14.1.5)
Well, OK, it isn’t that missing link but there is a
link between the autopilot and/or flight director and the autothrust. The A/THR
and the AP/FD work together to maintain speed and trajectory (altitude, glide
slope, vertical speed). If one is maintaining speed the other will maintain
trajectory and visa versa. If you think
about it you are used to doing this yourself when flying manually. On climb you
set climb power and maintain speed with pitch but when leveling for cruise at
altitude you use pitch to maintain altitude and power to hold speed. The Flight
Guidance acts in the exact same way. There are two basic ways the autoflight
maintains control.
AP or FD
in trajectory mode (example:
altitude hold, V/S, G/S) |
A/THR in
SPEED mode maintain
speed or MACH in cruise and approach |
Or
|
AP or FD
in SPD/MACH AP or FD
adjust pitch to hold speed |
A/THR in
THR mode Steady
thrust set to either THR CLB
(OPEN CLB) or THR IDLE
(OPEN DES) |
There are times that the autoflight cannot hold what has
been set and will have to change modes. This is called mode reversion when the
modes change automatically without the pilot calling for it. This is both a
part of normal flying and also part of the system to prevent flight outside the
envelope.
An everyday example is during a climb the autopilot normally
will control pitch to keep speed in OPEN CLB and the autothrust will maintain
climb thrust (THR CLB). On approaching level off at the target altitude pitch
will now revert from speed to vertical speed and thrust will revert from climb
thrust to speed. This will be true even if the pilot reselects a new altitude
before the level off is complete. The vertical speed mode will remain until the
pilot reselects something else.
Basically, be aware that if the autopilot is controlling
pitch then the autothrust is controlling speed and visa versa. Only one
controls pitch or speed at a time, never both controlling the same thing
together.
A common reversion mode is if the aircraft is climbing in
Open Climb or Managed Climb and the pilot is suddenly given a new altitude. The
new altitude is below the current altitude. The mode will revert to V/S set to
the current vertical speed upon reversion. The pilot can then change the
vertical speed to a descent or select Open Descent.
Reversions can also happen when hand flying if you don’t
follow the flight director. If in Open climb or descent and you allow the speed
to hit max or min the autothrust will go to SPEED mode and attempt to regain
the selected speed while the flight director bars will be removed! Turn OFF FD
when hand flying!
The FMA allows the pilot to know what modes the autoflight
systems are in and what can be expected. There are times when changes will
occur in the modes without pilot action. This mode reversion cannot be tracked
on the FCU, you must look at the FMA to know what is actually happening. The
FMA is broken into columns as shown below:
|
THRUST |
VERTICAL |
LATERAL |
APPROACH CAPABILITY STATUS |
AUTOFLIGHT ENGAGEMENT STATUS |
Each column has rows for messages and memos. There are up to
three rows available for each column to use. The first three columns, Thrust,
Vertical and Lateral have have the following rules:
Top row, Green – Active or Engaged, White - Armed
Middle row, Blue or Magenta – Armed (Magenta shows ALT CSTR
from FMGC)
Bottom row, Messages about flight control first priority
Bottom row, Messages about FMGS have second priority
|
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|
|
THR |
VERT |
LAT |
APP STAT |
ENGAG STAT |
|
ACTIVE, ENGAGED MODES |
MAN THR |
ALT* |
NAV |
CAT 3 |
AP 1+2 |
|
ARMED MODES |
|
G/S |
LOC |
DUAL |
1FD2 |
|
MEMOS, SPECIAL MESSAGES |
LVR ASYM |
SET HOLD |
SPEED |
||