OPERATIONAL PHILOSOPHY

FLIGHT CONTROLS

The relationship between the Pilot Flying’s (PF’s)
input on the sidestick, and the aircraft’s response,
is referred to as control law.

This relationship determines the handling
characteristics of the aircraft.

There are three sets of control laws,
and they are provided according to the
status of the: Computers,
peripherals, and hydraulic generation.

The three sets of control laws are:

• Normal law
• Alternate law
• Direct law.

OBJECTIVES

The aim of normal law is to provide the
following handling characteristics within the
normal flight envelope
(regardless of aircraft speed,
altitude, gross weight and CG):

• Aircraft must be stable and maneuverable

• The same response must be consistently obtained from the acft

• The Actions on the sidestick must be balanced in pitch and in roll.


The normal law handling characteristics,
at the flight envelope limit are:

• The PF has full authority to achieve Maximum aircraft Performance

• The PF can have instinctive/immediate reaction,
in the event of an emergency

• There is a reduced possibility of overcontrolling or
overstressing the aircraft.

Normal Law is the law that is most commonly available,
and it handles single failures.


CHARACTERISTICS IN PITCH

IN FLIGHT

When the PF performs sidestick inputs, a constant
G-load maneuver is ordered, and the aircraft
responds with a G-Load/Pitch rate.

Therefore, the PF’s order is consistent with the response
that is "naturally" expected from the aircraft:

Pitch rate at low speed; Flight Path Rate or G, at
high speed.

So, if there is no input on the stick:

• The aircraft maintains the flight path, even in case of speed changes

• In case of configuration changes or thrust variations,
the aircraft compensates for the pitching moment effects

• In turbulence, small deviations occur on the flight path.
However, the aircraft tends to regain a steady condition.

AIRBUS PITCH CHARACTERISTIC

Operational Recommendation:

From the moment the aircraft is stable and auto-trimmed,
the PF needs to perform minor corrections on the sidestick,
if the aircraft deviates from its intended flight path.

The PF should not force the sidestick, or overcontrol it.
If the PF suspects an overcontrol,they should release the sidestick.

AT TAKEOFF AND LANDING

The above-mentioned pitch law is not the most appropriate
for takeoff and flare, because the stable flight path is
not what the PF naturally expects.

Therefore, the computers automatically adapt
the control laws to the flight phases:

• GROUND LAW: The control law is direct law
• FLARE LAW: The control law is a pitch demand law.

Operational Recommendation:

Takeoff and landing maneuvers are naturally achieved.
For example, a flare requires the PF to apply permanent aft pressure on
the sidestick, in order to achieve a progressive flare.

Whereas, derotation consists of smoothly flying the nose gear down,
by applying slight aft pressure on the sidestick.


LATERAL CHARACTERISTICS

NORMAL CONDITIONS

When the PF performs a lateral input on the sidestick,
a roll rate is ordered and naturally obtained.

Therefore, at a bank angle of less than 33 °,
with no input on the sidestick, a zero roll rate is ordered,
and the current bank angle is maintained.

Consequently, the aircraft is laterally stable,
and no aileron trim is required.

However, lateral law is also a mixture of roll and yaw demand with:

‐ Automatic turn coordination

‐ Automatic yaw damping

‐ Initial yaw damper response to a major aircraft assymetry.

In addition, if the bank angle is less than 33 °,
pitch compensation is provided.

If the bank angle is greater than 33 °,
spiral stability is reintroduced and pitch
compensation is no longer available.

This is because, in normal situations,
there is no operational reason to fly
with such high bank angles for a long period of time.

AIRBUS LATERAL CHARACTERISTIC

Operational Recommendation:

During a normal turn (bank angle less than 33 °), in level flight:

• The PF moves the sidestick laterally
(the more the sidestick is moved laterally, the greater
the resulting roll rate - e.g. 15 °/s at max deflection)

• It is not necessary to make a pitch correction

• It is not necessary to use the rudder.

In the case of steep turns (bank angle greater than 33 °), the PF must apply:

• Lateral pressure on the sidestick to maintain bank

• Aft pressure on the sidestick to maintain level flight.