Flight Control Laws
(PH 12.1.5):
Multiple failures are required to revert from normal law.
“Multiple failures of redundant systems”
|
on
ground |
takeoff |
inflight |
landing |
on
ground |
|
Ground
Mode |
Flight
Mode |
Flight
Mode |
Flare
Mode |
Ground Mode |
|
Direct |
blend
from Direct to Normal |
Normal |
Normal
with slight pitch down added at 50’ for flare |
Direct |
Normal
Law: for a given amount of sidestick deflection a given amount of
G loading (pitch, elevators) or roll rate (roll, ailerons, spoilers) regardless
of airspeed. Pitch is always kept in trim automatically. Flare mode gives
slight pitch down after 50’ for flare. Bank past 33° requires constant input or
will automatically return to 33°. “Hard” protections. Green equals signs “=”
Normal Law Protections (think of as “A320 mode”):
|
Bank |
Yaw |
Pitch |
Low
Speed |
High
Speed |
Load |
|
Roll
rate proportional to side stick deflection 67° Max (at 45°
autopilot disconnect) |
Turn
Coordination & Yaw Dampening |
Load Factor proportional to stick deflection Max 30° nose up Max 15° nose
down |
Non-overrideable
AOA protection α
Prot Low
energy warn. α
Floor α
Max |
Non-overrideable
nose up command prevents overspeed at Vmo/Mmo |
Clean/Flaps
1 +2.5G/-1.0G Flaps Extended +2.0G/-0.0G |
Alternate
Law: Flight control will revert to alternate law after multiple
failures of redundant systems. Autotrim still available. “Soft” protections. No
protection in roll, roll goes to direct. Pitch goes to direct for landing when
landing gear extended (no “flare mode”).
It is possible to be in Alternate law without speed Stability and/or Yaw
Dampening. Aircraft can stall. Amber “X’s”
Alternate Law Protections (think of as “737-300 mode”):
|
Bank |
Yaw |
Pitch |
Low
Speed |
High
Speed |
Load |
|
Roll
Direct No
protections |
Yaw
Dampening |
Load Factor proportional to stick deflection No flare
mode, goes to direct for landing |
Low
speed stability Overrideable
nose down command to prevent stall Stall
Warning |
High
Speed Stability Overrideable
nose up command to prevent overspeed |
Clean/Flaps
1 +2.5G/-1.0G Flaps Extended +2.0G/-0.0G |
Direct
Law: Lowest level of flight control law. Proportional movement
between sidestick deflection and flight control deflection. No autotrimming. No
protections. Overspeed and Stall warnings available. The default mode on the
ground in all cases (think about it, if you are on the ground you cannot have a
G load or roll rate). This mode is most like a regular airplane (“DC-9 mode”).
Amber “USE MAN PITCH TRIM”
Abnormal
Law: This is entered by the aircraft being in an extreme unusual
attitude (about double normal limits). When back to normal attitude aircraft is
in Alternate Law except does not go to direct law on landing and no pitch
protections. Computer reverts to Abnormal when it sees the aircraft in unusual
attitude because computer logic says aircraft should not have been allowed by
normal law protections into this attitude in the first place, therefore
computer sees something is wrong.
Mechanical
Backup: Pitch through horizontal stab trim, Lateral through
rudders, Differential power. Both stab and rudder use cables going to
controller and require hydraulic power. Bottom line here, very little “manual
reversion” and if no hydraulic power you are a lawn dart. Red “MAN PITCH TRIM
ONLY”
Fly-by-wire, no feedback except for rudder and horizontal
stab trim
Two ELAC’s – Elevator, aileron and stabilizer control
Three SEC’s – Spoiler and standby elevator and stabilizer
control
Two FAC’s – Electrical rudder control (other warning
functions also provided)
FCDC’s (Flight Control Data Concentrators) process
information from ELAC’s and SEC’s and send data to the EIS and CFDS.
Pitch –
Controlled by elevators and horizontal stab. Electrically controlled by ELAC or
SEC and hydraulically actuated.
Elevator – Each
elevator has two hydraulic power sources and two actuators (one active and one
in damping mode).
Elevator
priorities: (Note: unless required by Ground School instructor I would not
memorize which hydraulic system supplies which flight control, I add it for
reference only)
ELAC 2 à ELAC 1 à SEC 2 à SEC 1
Left Elevator – Blue and Green hyd. Right Elevator – Yellow and Blue hyd.
Horizontal
Stabilizer – Electrically controlled by one of three motors or
mechanically controlled by the pitch trim wheels (through cable) and
hydraulically powered by green or yellow hydraulic. After touchdown the stab
trim is reset automatically to zero.
Horizontal Stab. Priorities:
ELAC 2 à ELAC 1 à SEC 2 à SEC 1
(same as elevators)
Roll
Control – provided by ailerons and spoilers. Electrically
controlled by ELAC (ailerons) or SEC (spoilers) and hydraulically actuated.
Ailerons – Each
aileron is powered by Green and Blue hyd. and has two actuators (one active and the other damping). The
ailerons droop 5° when the flaps are extended. If both ELAC’s fail then droop
is deactivated and the ailerons streamline and only spoilers are used for roll
control.
Aileron priorities:
ELAC 1 à ELAC 2
Green and Blue hyd.
Spoilers – Five
spoilers are installed on each wing. From the wing root to wing tip they are
numbered 1 through 5. All are used as ground spoilers. Numbers 2 through 5 (the
4 outboard spoilers) provide roll control. The middle three (2 – 4) provide in-flight speed brakes. If a SEC
fails the spoiler(s) it controls is automatically retracted (if extended) and
that spoiler(s) deactivated. There is no reversion to other computers.
Spoiler priorities:
Spoilers 1 & 2 - SEC 3, Yellow and Green
Spoilers 3 & 4 - SEC 1, Yellow and Blue
Spoiler 5 - SEC 2, Green
Green SPD BRK memo on ECAM when speedbrakes extended.
Flashes amber when thrust is applied with speedbrake extended.
Speedbrake extension inhibited when (SAFE-T):
A - Angle of Attack protection active (α prot) or ALPHA
FLOOR active
F - Flaps at FULL setting (also config 3: A321)
E - Elevator (L or R) fails (spoilers 3 and 4 only)
T-TOGA on thrust levers (OK, really above MCT but you better
be in the TOGA detent if you are above MCT!)
If speedbrakes out when inhibited they will automatically
retract. Must restow speedbrake handle for 10 seconds to regain. Do not use
speedbrakes below 1000’ AFE.
If one speedbrake on one wing fails the corresponding one on
the other wing will be inhibited for symmetry.
Ground Spoilers are armed by raising the Speed Brake Lever.
The speed brake lever does not move with auto extension.
Ground Spoilers extend automatically:
Partial Extension – On landing –
Reverse selected on at least one engine with other at or
near idle –and– one main landing gear strut compressed
Full Extension – On landing or on takeoff above 72 kts.
(rejected takeoff) –
Both thrust levers at idle (spoilers armed) –or–
Reverse thrust selected on at least one engine with other at
idle (spoilers not armed) and both mains compressed.
Rudder – Rudder
controls yaw. FAC 1 & 2 provide electric control through trim motors and
hydraulically actuated. Mechanically controlled by rudder pedals if FAC’s fail.
Rudder deflection is normally limited according to airspeed but during dual FAC
failure full rudder deflection is available when the slats extend. Rudder trim
is automatic but can be done manually using electric RUD TRIM switch. A rudder
trim RESET pb will reset the rudder to 0 trim (not available during autopilot
operation).
ELACs sends signals to FACs and FACs compute yaw damper and
turn coordinations. No feedback (rudder pedal movement) during yaw damper
corrections or turn coordination.
FAC – think of a southern Dragnet, “just the FACs y’all”
A – Angle of Attack (flight envelope protection - AoA, High
and Low speed limits)
W – Windshear
L – Low Energy warning (speed, speed)
α Prot – Alpha Protection, Angle of attack protection
speed, top of amber tiger stripe
A – Angle of Attack instead of Load Factor (g’s)
S – Speedbrakes retract
A – Autopilot disconnects
P – Pitch trim inhibited
The flap handle has a “trigger” that must be squeezed to
allow the flaps to move out of detent with balks at 1 and 3 to prevent
“overshoot”. The flaps will only provide the configurations that are allowed
for each detent, there is no “in between the detents” positioning. The flap
handle controls both flaps and slats. Controlled by two Slat Flap Control
Computers (SFCCs).
Both flaps and slats are powered by two hydraulic systems,
flaps by green and yellow and slats by green and blue. If any hydraulic system
fails leaving only one hydraulic system powering either slats or flaps the
single powered control will extend and retract at half speed. If only one SFCC
is functional the flaps and slats will operate at half speed.
The flaps have 5 selected positions: 0, 1, 2, 3 and FULL.
Takeoff is allowed with 1, 2 or 3
Landing is allowed with 3 or FULL
Note: when landing with Flaps 3 the LDG FLAP 3 pb on the
GPWS overhead panel should be selected ON to prevent GPWS flap warnings when
landing and also CONFIG 3 selected in PERF APPR for proper approach numbers.
The flap position numbers are just that, position numbers,
they do not correspond to degrees of flaps (or slats) and in fact each model
(the A319, A320 and A321) has slightly different flap deflection schedules for
certain flap lever positions. For example, Flaps FULL for the A319 is 40°, A320
is 35° and the A321 is 25°. The A321 also has additional slots built into the
flaps to provide additional lift at slower speeds. Procedures remain the same
for all models except for higher flap speeds on the A321. The flap “indicator”
is in the E/WD and shows the amount of extension for both slats and flaps, with
three positions for the slats and four positions for the flaps.
Flaps 0 (zero) is flaps “UP” with all trailing and leading
edge flap devices fully stowed.
Flaps 1 is a “hybrid” with two separate configurations for
the same Flaps 1 handle position. However, from a pilot standpoint the
difference is transparent as the flap handle is treated the same. Flaps 1
position will provide flaps 1+F for takeoff and anytime you are retracting
flaps from a higher setting (2, 3 or FULL). Any other time Flaps 1 will provide
Flaps 1 (how about that?). OK, so what is the difference between Flaps 1 and
Flaps 1+F? Glad you asked, simply this, the trailing edge flaps. The trailing
edge flaps make up the +F as Flaps 1 is slats only in the initial position.
During Flaps 1+F the slats and flaps will extend to initial positions.
Now that I have you completely confused, here is the short
story:
Ø Flaps 1 on
ground extending for takeoff – Flaps 1+F (slats and flaps)
Ø Flaps 1
after takeoff during initial flap retraction from Flaps 2 or 3 – Flaps 1+F
(slats and flaps)
Ø Flaps 1
for landing extending from Flaps 0 – Flaps 1 (slats only)
Ø Flaps 1
for Go Around retracting from 2, 3 or FULL – Flaps 1+F (slats and flaps)
As you can see the only time Flaps 1 gives you Flaps 1
(slats only) is on extension for landing, the rest of the time Flaps 1 is Flaps
1+F (slats and flaps). The E/WD will show either Flaps 1 or Flaps 1+F depending
on configuration.
Flaps 2, 3 and FULL all have both slats and flaps extended
to some degree.
Flaps have overspeed protection at flap setting 1+F so that
at 210 KIAS the flaps will automatically retract to Flaps 1 (slats only).
Please note on the A321 it is possible at high gross takeoff weights that F
speed will exceed the flap speed for 1+F. In this case the flaps will
automatically retract and the pilot will select flaps 0 at S speed which will
retract the remaining slats.
Slats have an alpha lock function that inhibits them from
retracting from position 1 to 0 when at a high angle of attack or low airspeed.
There are 4 Wingtip Brakes (WTB) that will lock the flaps or
slats in case of asymmetry, overspeed, runaway or uncommanded movement. WTB’s
cannot be released in-flight. If flaps are locked out, slats can operate and
visa versa.
Sidesticks
(PH 12.2.2)
Perhaps one of the most distinctive and noticeable
differences in the Airbus 320 series from other airliners is the sidestick.
Most folks get comfortable with the sidestick within minutes. However, the
computerized flight controls that the sidestick activate require some new
features:
No feedback (feel) is given. Sidestick is spring loaded to
neutral.
System algebraically sums the signals from both sticks if
both are operated at the same time (dual input). However, the total input is no
more than the max input from a single stick.
A red Takeover pb in the sidestick (also serving as
autopilot disconnect) allows one pilot to override the other or to disable a
damaged sidestick. If priority is taken an audio “PRIORITY LEFT (or RIGHT)” is
sounded.
A red arrow light will illuminate in front of the pilot who
has been deactivated when one pilot has taken priority over the other. A green
CAPT or F/O light will illuminate in front of the pilot with priority if the
other sidestick is out of neutral.
Last pilot to press Takeover pb has priority.
Pressing Takeover pb for 40 secs. will latch the priority
condition (pilot does not have to continue to press Takeover pb). However, a
deactivated sidestick can be reactivated by momentarily pressing the Takeover
pb on either sidestick.
Green CAPT and F/O sidestick priority lights will flash
during dual input and an audio “DUAL INPUT” will be sounded.
The Takeover pb and dual input warning system are commonly
misunderstood. A green light in front of you means dual input or you have just
taken priority in a dual input situation and a red arrow means your sidestick
has been deactivated. These are two different things. Dual input is almost
always unintentional and unwanted. The takeover priority may be something that
needs to be done if a sidestick has gone bad or some other problem has
occurred. However, if YOUR sidestick is bad the OTHER pilot must latch it out
with their Takeover pb.
Sidestick “locks” in place when on autopilot. Pilot action on sidestick (or trim wheel) at any time will disconnect the autopilot.