Airbus Flight Control Systems

All modern Airbus aircraft (except for the A300 and A310) utilize a “Flight Control System” that enforces Airbus flight control laws, which are a set of protocols defining how the aircraft responds to pilot inputs.

The A330 aircraft has a total of five flight control computers, including three primary computers (PRIM1, PRIM2, PRIM3) and two secondary computers (SEC1, SEC2). If necessary, the aircraft can be operated by any single flight control computer, adhering to the simplest Airbus flight control law—the “Direct Law”.

Flight control surfaces are manipulated electronically or hydraulically, and the computers’ role is to prevent the aircraft from exceeding safe flight envelope limits regarding pitch, roll, angle of attack, and airspeed.

Three flight control laws are supported: Normal Law, Alternate Law, and Direct Law. Alternate Law is further subdivided into Alternate Law 1 and Alternate Law 2.

Normal Law During normal flight, Normal Law provides control for pitch, roll, and yaw.

1 Ground Mode When the aircraft is on the ground, Ground Mode is active. There is a direct relationship between sidestick pitch input and elevator response.

2 Flight Mode Once the aircraft is airborne and remains below 100 feet during the landing phase, Flight Mode gradually replaces Ground Mode over a 5-second interval. Flight Mode includes pitch attitude, angle of attack, load factor, high speed, and bank angle protections. When the sidestick is neutral, the flight control system maintains a load factor of 1g. During a turn, the load factor is automatically adjusted in proportion to sidestick deflection. Additionally, during a turn, the flight control system automatically corrects as needed to maintain Level Flight (for bank angles up to 33°). If the aircraft climbs or descends during a turn, the system attempts to maintain the original 3D geometric path. This means the pilot does not need to apply back pressure on the sidestick during a turn. However, if the bank angle exceeds 33° or the load exceeds 1.3g, the automatic correction is disengaged. The flight control system ensures the load factor remains within the range of -1g to +2.5g, and the pitch angle is between -15° and +30°. Therefore, regardless of sidestick input, the pilot cannot exceed these limits. At the lower end of the speed range (amber band), the system ensures the angle of attack does not exceed the maximum allowable value (marked as a-max). High-speed protection activates automatically when the maximum operating speed (Vmo) is exceeded. The system reduces the sidestick’s pitch authority and applies a continuous pitch-up command until the speed drops below Vmo, at which point Normal Law is restored. During a turn, the system will not allow the aircraft to exceed a bank angle of 67°; even with maximum sidestick deflection, when pressure is released, the aircraft will return to a 33° bank angle.

3 Flare Mode This mode activates automatically when the radio altimeter indicates an altitude of 100 feet or lower. Sidestick pitch input is converted directly into the corresponding movement of the elevator. When the altitude reaches 50 feet or lower, the system issues a pitch-down correction command, requiring the pilot to increase pitch-up to achieve the desired flare (nose-up) attitude upon touchdown.

Alternate Law Alternate Law becomes effective in the event of one or more critical flight control component failures.

Alternate Law 1 (ALT1) This law is activated when there are faults in two of the following: elevators, yaw dampers, flaps, or slats. Lateral control is unaffected and still follows Normal Law. However, the system no longer provides automatic pitch protection.

Alternate Law 2 (ALT2) This law is activated when two IRS/ADR units fail, or there are faults in the ailerons or spoilers, or a loss of Thrust on two engines. Lateral control no longer follows Normal Law but instead adopts Direct Law (see below). The system provides neither automatic pitch protection nor bank angle protection.

Direct Law This law is activated in the event of total failure of flight computers or IRS/ADR units, failure of two elevators, or loss of Thrust on two engines. Pilot inputs are converted directly into the corresponding movement of the control surfaces.

Cockpit Walkthrough

In this section of the manual, the cockpit is broken down into different functional areas, identifying and describing the controls within them. This will aid in locating the necessary instruments and controls for later use of aircraft checklists and flying the aircraft.

Forward Overhead Panel The Forward Overhead Panel consists of a series of smaller panels used to manage the aircraft’s electrical, pneumatic, lighting, pressurization, engine start, and other systems. In the three-crew era, many of these were the responsibility of the flight engineer.

Note: Not all functions within these panels are fully simulated in the X-Plane A330-300 model. The Aft Overhead Panel is not included as it supports secondary functions that are not modeled.

1. ADIRS This panel controls the aircraft’s three Inertial Reference System (IRS) units and three Air Data Inertial Reference (ADR) units.

IRS units are gyroscopic accelerometers that detect acceleration on the lateral and vertical axes. The IRS system provides independent data sources for onboard navigation systems to determine the aircraft’s position in 3D space. This is necessary without external references, such as satellites or ground navigation aids.

ADR units collect data from aircraft probes and sensors, providing information on airspeed, barometric altitude, temperature, and angle of attack.

ON BAT = The IRS system is operating on battery power before flight. IR1 / IR2 / IR3 Indicator Lights ALIGN: The IRS unit is calibrating and is not yet ready for navigation. FAULT: The IRS unit is unable to provide data. OFF: The IRS unit is powered off.

Knobs: OFF: Sets the IRS unit to off. NAV: Normal navigation mode. ATT: Attitude and Heading Only mode. ADR1 / ADR2 / ADR3 Indicator Lights FAULT: The ADR unit is unable to provide data. OFF: The ADR unit is powered off.

2. APU Fire If a fire occurs in the Auxiliary Power Unit (APU), this annunciator light will illuminate accompanied by an aural warning. Lifting the guard and clicking the “FIRE” button cuts off the fuel supply to the APU. This also illuminates the “AGENT” button. Clicking this button will discharge the fire extinguishing agent.

3. Flight Control Panel (Left) 【See: 12. Flight Control Panel (Right)】 The A330 employs a computer-controlled “Fly By Wire” system (see Airbus Flight Control Systems) that translates pilot commands into the required movements of control surfaces (ailerons, elevators, rudder, and flaps). This panel and its twin panel on the top right control which computer systems are active. There are three primary systems for redundancy, and two secondary systems provide additional redundancy with reduced automation levels. TURB DAMP: Enables the (automated) Turbulence Damping System. PRIM1: Activates Primary Flight Control Computer system 1. SEC 1: Activates Secondary Flight Control System 1, which supports only Direct Law.

4. Multi-Purpose Panel INR TK SPLIT: Not simulated. EVAC COMMAND: Activating this guarded switch notifies the crew to begin evacuating the cabin during a ground emergency. EVAC HORN OFF: Stops the evacuation warning sound in the cockpit. EVAC CAPT & PURS: The position of this switch determines whether the evacuation warning can be triggered by both the Captain and cabin crew, or solely by the Captain. EMER GEN TEST / LAND RECOVERY / EMER GEN / MAN ON: Not simulated. TERR: Defaults to ON. When turned off, it inhibits automatic “TERRAIN” (proximity) voice callouts. SYS: Defaults to ON. When turned off, it inhibits all automatic voice callouts. G/L: Defaults to ON. When turned off, it inhibits automatic “GLIDESLOPE” (deviation) voice callouts. FLAP MODE: Defaults to ON. When turned off, it inhibits automatic “TOO LOW FLAPS” voice callouts. MASK MAN ON: Defaults to AUTO. This guarded switch deploys passenger oxygen masks. PASSENGER: Clicking this button deploys additional oxygen masks in the passenger cabin. CREW SUPPLY: Defaults to ON, providing supplemental oxygen to the crew in case of cabin pressurization emergencies. Manually toggling this button to OFF stops the oxygen flow. CALL buttons: These buttons call crew members and ground services. Not simulated. RAIN RPLNT: Clicking this button injects rain repellent fluid onto the windshield in flight. Not simulated. WIPER (Knob): Activates the two speed modes of the windshield wipers.

5. Engine Fire Panel If a fire occurs in the left or right engine, the relevant warning light will illuminate and an aural warning will sound. Lifting the guard and clicking the “FIRE” button cuts off the fuel supply to that engine. This also illuminates the “AGENT” buttons. Clicking these buttons discharges the fire extinguishing agent, and if necessary, a secondary agent.

6. Hydraulic and Fuel Control Panel There are three hydraulic systems used to control wing surfaces - Blue, Green, and Yellow. In normal operation, each system is responsible for different control surfaces, but redundancy can be provided for a failed system in the two remaining systems. Normal operation utilizes two engine-driven pumps and three electric pumps for redundancy.

ENG Buttons: Indicate the status of the two engine-driven pumps. When unlit, they default to ON. If a fault occurs, the relevant button will illuminate. Clicking one of these buttons toggles the mode to OFF, shutting down that pump.

ELEC Buttons: Indicate the status of the three electric pumps. When unlit, they default to OFF. Clicking one of these buttons toggles the mode to ON, starting that pump.

There are four fuel tanks - Left (Wing), Center, Right (Wing), and (Tail) TRIM tank. The wing tanks have three fuel pumps supplying the engines (L1, L2, L STBY), and the center tank has two fuel pumps (CTR L and CTR R). The T TANK XFR pumps are used to transfer fuel between the TRIM tank and the center tank.

These buttons default to ON or AUTO when unlit. If a fault occurs, the relevant button will illuminate. Clicking one of these buttons toggles the mode to OFF, shutting down that pump.

Clicking an XFR button toggles the mode to Manual (MAN). In manual mode, fuel is no longer transferred automatically between the center tanks.

Clicking a MODE button toggles the mode to Manual (MAN). The adjacent guarded switches can then be used to control fuel transfer from the Trim Tank at the rear to the center tank.

Clicking the WING X FEED (Cross Feed) button opens a valve, allowing fuel to be fed from a wing tank on one side to the engine on the opposite side. This is used if the normal fuel supply for that engine fails.

7. Electrical System Control Panel BAT: Displays the voltage of the selected electrical bus (BAT 1, BAT 2, or APU). BAT 1 / BAT 2: Default to OFF. Clicking these buttons powers up the electrical buses fed by Battery 1 and Battery 2. APU BAT: Defaults to OFF. When the aircraft is not connected to external power, clicking this button toggles the mode to ON to start the Auxiliary Power Unit (APU). AC ESS FEED: Clicking this guarded button switches the power source for the AC (Alternating Current) Essential bus from BAT 1 to BAT 2. GALLEY: Clicking this button cuts power to the galley areas. COMMERCIAL: Clicking this button cuts power to the commercial electrical bus, which powers systems supporting commercial operations (e.g., passenger cabin amenities, cargo holds, etc.).

IDG: Clicking any of these guarded buttons disconnects the Integrated Drive Generator (IDG) associated with the relevant engine. These generators convert some of the mechanical energy from the engine into electrical energy. If the IDG’s oil cooling system fails, it must be disconnected from the engine before further damage occurs. Once disconnected, it cannot be reset in flight, and that engine will no longer produce electricity.

GEN: Clicking any of these buttons stops the relevant engine’s generator from supplying power to the main electrical buses. APU GEN: Clicking this button stops the APU’s generator from supplying power to the main electrical buses. EXT A / B: Clicking these buttons draws power from external ground power connected to port A or B.

8. Air Conditioning Panel RAM AIR: Opens an external vent to provide emergency ventilation to the cockpit and cabin.

PACK 1 / 2: Default to OFF. Clicking these buttons activates the relevant pneumatic air cycle machine (PACK). This provides pressurized and conditioned air to the cockpit and cabin using surplus “bleed” air from the engines or APU.

ENG BLEED 1 / 2: Default to OFF. Clicking these buttons opens valves to supply surplus “bleed” air from the relevant engines to PACK 1 and PACK 2.

APU BLEED: Default to OFF. Clicking this button opens a valve to supply surplus “bleed” air from the APU to PACK 1 and PACK 2.

PACK FLOW: This knob controls the rate at which bleed air enters the cabin. COCKPIT / CABIN Knobs: Control the temperature for the cockpit and cabin, respectively.

Cross Bleed Knob: When set to AUTO, automatically transfers bleed air between PACK 1 and PACK 2 as needed. The crew can override this function by setting this knob to OPEN or CLOSED.

9. Lighting Panel APU MASTER SW: Opens a flap to direct external air to the Auxiliary Power Unit (APU).

START: Starts the APU. The startup process takes a while to reach 100% RPM, at which point “Avail” illuminates on the button, indicating bleed air is now available for engine start.

ICE IND & STBY COMPASS: Illuminates the ice indicator located on the outside of the center windshield post. Visible by the crew through the windows. This switch also illuminates the standby magnetic compass located on the inside of the center windshield post.

DOME: Illuminates the dome light in the cockpit ceiling. The switch on the right controls brightness.

ANN LT: Controls the brightness of cockpit annunciator lights. Test mode illuminates all lights.

SEATBELTS / NO SMOKING: Illuminates the respective signs in the cabin.

EMER EXIT LT: Defaults to ARM (Armed), meaning emergency exit lights will illuminate in case of power failure. The crew can manually switch to ON and OFF positions to override this setting.

STROBE: This switch controls the external flashing lights installed on the wingtips and tail assembly. When set to AUTO, lights will be active when the struts are not compressed (aircraft is airborne).

BEACON: Illuminates the red flashing light on top of the fuselage.

WING: Activates lights installed on the fuselage to illuminate the wing leading edges for ice inspection.

NAVE & LOGO. In position 1, illuminates the white, red, and green navigation lights. In position 2, illuminates lights on the horizontal stabilizer to highlight the logo on the vertical stabilizer.

LAND: Illuminates the landing lights installed on the wings.

TAXI: Illuminates the taxi lights installed on the nose landing gear, with a choice between taxi mode or takeoff mode (higher brightness).

10. Audio Control Panel This panel replicates the functions of the dual audio control panels located on the central console for the Captain and First Officer, respectively. The aircraft is equipped with two Very High Frequency (VHF) transceivers, two High Frequency (HF) transceivers, an interphone system between flight crew, and an interphone system between cockpit and cabin crew.

The top row of buttons controls which transceiver is currently being used for transmission. When a button is illuminated, it indicates that the corresponding transceiver is transmitting.

The second row of knobs controls which transceivers can be heard. By default, if a transceiver is selected for transmission, it can also be heard. However, it is possible to listen to other transceivers by clicking the relevant knob (it will illuminate). The knobs are also used to control the volume for that audio channel.

VOR 1/2: Click this knob to enable the (Morse) audio from the currently tuned VOR 1 or VOR 2 receiver. Rotate the knob to adjust the volume.

ADF 1/2: Click this knob to enable the (Morse) audio from the currently tuned ADF/NDB 1 or ADF/NDB 2 receiver. Rotate the knob to adjust the volume.

11. Radio Management Panel This panel replicates the functions of the dual Radio Management Panels located on the central console for the Captain and First Officer, respectively. The aircraft is equipped with two Very High Frequency (VHF) transceivers, two High Frequency (HF) transceivers, an interphone system between flight crew, and an interphone system between cockpit and cabin crew.

VHF 1 / VHF 2: These buttons select the VHF transceiver controlled by this panel. HF1 / HF 2: These buttons select the HF transceiver controlled by this panel. Multi-function Knob: The outer knob adjusts the integer part of the standby radio frequency, and the inner knob adjusts the decimal part of the standby radio frequency.

The “<->” button toggles the standby and active radio frequencies. ON/OFF: This switch toggles the power for the entire panel. STBY NAV switch: Not modeled.

Note: The MCDU supports tuning navigation aid frequencies (ILS/VOR/ADF). This is detailed in the Central Console section. Additionally, a separate manual for the Airbus MCDU will be published in the future.

12. Flight Control Panel (Right) [See: 3. Flight Control Panel (Left)] The A330 is equipped with a computer-controlled “Fly By Wire” system (see Airbus Flight Control Systems) that translates pilot commands into the required movements of control surfaces (ailerons, elevators, rudder, and speed brakes). This panel and its twin on the top right control which computer systems are active. There are three primary systems for redundancy, and two secondary systems for additional redundancy with reduced automation levels.

PRIM2: Activates Primary Flight Control Computer system 2. PRIM3: Activates Primary Flight Control Computer system 3. SEC 2: Activates Secondary Flight Control System 2, which supports only Direct Law.

13. Multi-Purpose Panel ISOL VALVES: Default to open. Clicking these buttons isolates the relevant cargo compartment from the heating and ventilation system. Typically done when the cargo hold is empty. COOLING Knob: Sets the temperature for the cargo compartment. HOT AIR: Defaults to open. Clicking this button closes the hot air duct to the cargo compartment. CARGO SMOKE buttons: Not modeled. AVNCS: Not modeled. EXTRACT: Defaults to auto. Clicking this button turns off the exhaust fan for avionics/electronics (air cooling). CAB FANS: Defaults to open. Clicking this button turns off the fans circulating air in the cabin. ENG Buttons: Not modeled. WIPER Knob: Sets the speed of the windshield wipers.