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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.
Make 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’
US Airways Airbus A319, A320, A321 Notes
55
Missing Link or AP/FD & A/THR interaction
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.
US Airways Airbus A319, A320, A321 Notes
56
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!
Airbus Gotcha: or How to be an Airshow Pilot: You are hand flying with the
flight director on (bad thing!). You are getting ready to level off just prior to the
Final Approach Fix on an approach. However, you are not quite level at the set
altitude and the FMA does not yet show ALT* for capture. You are slowly leveling
off just a little high without realizing it and as you have been in Open descent the
thrust remains in the commanded idle. Speed decays to below VLS. Suddenly
climb thrust is commanded even though you are now wanting to continue
descent. Sounds like a flyby to me!
US Airways Airbus A319, A320, A321 Notes
57
FMA – Flight Mode Annunciator
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
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