Airbus A320 Master Question Bank Study Guide

Electrical and Lighting Systems

The Airbus A320 electrical system utilizes engine-driven and APU generators, each rated at a maximum continuous load of $90\,KVA$. The normal priority for supplying electrical power to the AC buses is as follows: engine generators, followed by external power, and finally the APU. Under normal operations, the BATTERY BUS is powered by DC bus 1 through a DC tie contactor. In the event of a total loss of AC power while airspeed is above $50\,kts$, an inverter connects to the HOT BATTERY BUS to supply AC power specifically to the AC ESS bus.

The AC ESS FEED switch, located on the overhead panel, allows the power source for the AC ESS bus to be shifted from AC bus 1 to AC bus 2. If airspeed is above $100\,kts$, the emergency generator is capable of powering the AC ESS bus. Regarding internal lighting, the FASTEN SEAT BELT, NO SMOKING, and EXIT signs activate automatically whenever the cabin altitude exceeds $11,300\,feet$, regardless of the physical switch positions on the flight deck.

Operational protections for electrical components include a limit on the IDG DISCONNECT switch; it should not be pressed for longer than approximately $3\,seconds$ to prevent damage to the disconnect mechanism. A FAULT indication on the BAT pushbutton signifies that the charging current is outside its established limits. For the IDG pushbutton, a FAULT indication identifies either an IDG oil overheat or low oil pressure. Automatic load shedding occurs if a generator exceeds $100\%$ of its rated output: the main galley buses and in-seat power supplies are shed. If the aircraft is operating with only a single generator (either on the ground or in flight), all galley buses and in-seat power supplies are shed. The RAT & EMER GEN indicator on the EMER ELEC PWR panel displays a red FAULT if AC BUSES 1 & 2 are not powered and the emergency generator is failing to supply electrical power. If avionics smoke is detected and the GEN 1 LINE pushbutton is selected OFF, GEN 1 is isolated from the aircraft except for powering one fuel pump in each wing tank.

Fire Protection and Smoke Detection

Engine fire detection is comprehensive, with sensors installed in the pylon nacelle, the engine core, and the fan section, though not in the fuel/oil heat exchanger. Each engine's system utilizes two loops, with each loop containing three heat sensing elements. If both fire loops fail within $5\,seconds$ of each other, a FIRE warning is triggered. In the case of general component failure, the ECAM system issues appropriate alert messages. If an APU fire occurs in flight, the APU will automatically shut down, but the pilot must manually discharge the fire bottle. On the ground, the APU fire protection involves automatic shutdown and automatic bottle discharge.

Cargo compartment protection features two extinguisher bottles that can be discharged into either the forward or aft compartments. The engine fire extinguisher squib is armed only when the ENG FIRE pushbutton is pushed and released. Smoke detection in the cargo area is signaled by a red SMOKE light if both channels detect smoke, or if one channel detects smoke while the other is inoperative. When the APU FIRE pushbutton is activated (pushed and released), it closes the HP fuel valve, the APU bleed valve, and the crossbleed valve. A DISCH light on the AGENT pushbuttons indicates that the extinguisher bottle has lost pressure. A GEN 1 LINE smoke light on the EMER ELEC PWR panel specifically indicates smoke within the avionics ventilation duct.

Powerplant and FADEC Management

The Full Authority Digital Engine Control (FADEC) manages fuel metering, start sequencing, and engine operating limits for both forward and reverse thrust. It computes thrust rating limits based on the measured thrust lever angle (TLA). FADEC is powered by a dedicated alternator that is independent of the primary aircraft electrical system. During an automatic start sequence, FADEC will abort if it detects a hot start, no ignition, a stalled start, or a start valve fault. The system features three idle modes: modulated idle, approach idle, and reverse idle.

Engine ignition consists of two independent circuits (A & B) alternated by FADEC during each autostart. Continuous ignition is provided automatically when the Engine Mode selector is in NORM if engine anti-ice is ON, a flameout is detected, or the EIU fails. Thrust levers feature $5\,detents$: TOGA, FLX/MCT, CLimb, IDLE, and MAX REVerse. A manual start differs from an automatic start in that the pilot must manually open the start valve via the ENG MAN START pushbutton. For thrust reverse deployment, the system requires a signal from at least one SEC detecting ground spoiler deployment, a TLA reverse signal from at least one SEC, left and right main gear compression signals from the LGCIU, and at least one operating FADEC channel coupled with a thrust lever reverse signal. The APU has its own dedicated fuel pump and can be started via batteries, external HP air, or normal aircraft power; the sequence is fully automatic.

Navigation, Instruments, and FMGS

The Electronic Instrument System (EIS) displays data across $6\,identical$ display units. Three Display Management Computers (DMCs) process inputs to generate these images. The aircraft is equipped with $3\,Air Data Inertial Reference Units (ADIRUs)$. The Flight Management Guidance Computers (FMGCs) handle flight management and flight guidance, operating in independent, single, or dual modes. Aircraft position is determined using a hybrid IRS/GPS calculation. Flight guidance has two modes: Managed (following long-term profiles set by the FMGS) and Selected (following short-term targets set on the FCU). Navigation aids are typically autotuned by the FMGC.

Visual cues on the Flight Mode Annunciator (FMA) use color coding: engaged modes appear in Green, while armed modes appear in Blue or Magenta. Radio Height is shown on the PFD whenever the aircraft is below $2,500\,feet$. The ON BAT light on the ADIRS CDU indicates that one or more ADIRUs are running on battery power alone. If ADR 1 or 2 fails, the AIR DATA selector allows the pilot to switch to ADR 3. A critical takeoff limitation is the FLEX TEMP; if it is not entered in the MCDU, a FLEX takeoff becomes unavailable. The ECAM EMER CANC pushbutton cancels warnings/cautions but cannot cancel OVERSPEED or L/G NOT DOWN alerts.

Flight Controls and Laws

A320 flight control surfaces are electrically controlled and hydraulically actuated. ELAC 2 is the primary computer for the elevators and horizontal stabilizer. If both sidesticks are operated at once, the inputs are algebraically summed, accompanied by a "DUAL INPUT" aural message. Roll control uses ailerons assisted by the four outboard spoilers on each wing. When flaps are extended, the ailerons droop $5\,degrees$. If a SEC (Spoiler Elevator Computer) loses power, its associated spoilers retract automatically. Speed brake extension is inhibited if angle of attack protection is active or if flaps are in the FULL configuration.

The aircraft features mechanical backup for the horizontal stabilizer and the rudder. In Normal Law, pitch trim is automatic regardless of autopilot engagement. If the angle of attack exceeds alpha prot, the system enters alpha protection mode. Alpha floor protection provides TOGA thrust regardless of the thrust lever position. In Direct Law, the PFD displays the message "USE MAN PITCH TRIM." When landing gear is extended while in Pitch Alternate Law, the system degrades further to Pitch Direct Law. If all electrical flight control signals are lost, the aircraft reverts to Mechanical Backup, though hydraulic power remains necessary for operation.

Fuel and Pneumatic Systems

The fuel system contains $6\,main$ pumps (excluding the APU pump). Suction feeding is only possible from the wing tanks if the pumps fail. Fuel transfers from outer to inner wing cells when inner cell levels drop to $1,650\,lbs$. The center tank pumps in AUTO mode run for $2\,minutes$ after engine start, stop when slats are extended, and run for $5\,minutes$ once the center tank is empty. The fuel crossfeed valve is driven by $2\,motors$. Low-pressure fuel valves are controlled by either the engine MASTER switch or the ENGINE FIRE pushbutton.

Pneumatic air comes from IP or HP engine bleeds. The HP bleed valve closes automatically if upstream pressure is too low or too high, or if closed electrically. The APU bleed valve is electrically controlled and pneumatically operated. Leak detection uses a single loop in the wings, pylons, and APU. The crossbleed valve features two electric motors, allowing for both automatic and manual modes. If an ENG BLEED FAULT light illuminates, it will extinguish when the switch is selected OFF, even if the fault persists.

Air Conditioning and Pressurization

Temperature is regulated by one zone controller and two pack controllers. If an air cycle machine fails, the affected pack operates purely as a heat exchanger. If both channels of a pack controller fail, the pack valve closes. If the zone controller fails entirely, the packs deliver fixed temperatures ($68\,^{\circ}F$ from Pack 1 and $50\,^{\circ}F$ from Pack 2). Airflow defaults to HI if the APU is supplying bleed air or if one pack fails. Selecting the RAM AIR switch to ON opens the outflow valve, provided the differential pressure ($\Delta p$) is less than $1\,psi$.

The pressurization system uses two automatic controllers that alternate after each landing. There are $3\,motors$ that drive the outflow valve. Manual pressurization is engaged by selecting the MODE SEL pushbutton to MAN. In cargo heating, selecting the AFT ISOL VALVE to OFF shuts the inlet/outlet valves, the trim air valve, and the extraction fan. The lavatory/galley extract fan runs continuously as long as electrical power is available.

Hydraulic Systems and Landing Gear

The A320 uses three hydraulic systems: Green, Blue, and Yellow. Green and Yellow have engine-driven pumps, while Blue and Yellow have electric pumps. The Ram Air Turbine (RAT) powers the Blue system and deploys automatically if AC 1 & 2 are lost and airspeed is above $100\,kts$. The PTU transfers power between Green and Yellow when the pressure differential exceeds $500\,psi$. Landing gear operation is managed by LGCIUs that alternate roles after each gear cycle. Gear hydraulics are cut off by a safety valve when airspeed exceeds $260\,KIAS$.

Autobraking initiates above $72\,kts$ upon ground spoiler extension. The DECEL light illuminates when the actual deceleration reaches $80\%$ of the selected rate. In the alternate brake system, anti-skid and autobrake are inoperative. The alternate brake accumulator provides at least seven full brake applications. Nose wheel steering via tillers allows $+/- 75\,degrees$ of movement; via pedals, steering reduces from $20\,kts$ until it reaches $0\,at\,130\,kts$. Emergency gear extension requires $3\,clockwise$ turns of a handcrank, which shuts off hydraulic pressure and unlocks the gear for gravity extension.

Ice, Rain, and Oxygen Systems

Wing anti-ice uses pneumatic bleed air to protect the three outboard slats; valves close automatically if a leak is detected. On the ground, wing anti-ice valves only open for a $30\,second$ test. Engine anti-ice valves fail to the OPEN position if electrical power is lost, while wing valves fail CLOSED. Engine anti-ice activation increases minimum and idle $N1$. Probe heat is automatic whenever an engine is running or the aircraft is in flight.

Cockpit oxygen is supplied by a high-pressure cylinder, while passenger oxygen uses chemical generators. Passenger masks drop automatically at $14,000\,feet$ cabin altitude and provide oxygen for approximately $15\,minutes$. Air begins flowing to passengers only when a mask is pulled toward the seat. Thermal discharge of the oxygen system is signaled by a green disk on the fuselage. Cockpit masks provide $100\%$ oxygen automatically above $35,000\,feet$.

Communications Systems

Radios are controlled via three Radio Management Panels (RMPs). In the Emergency Electrical Configuration, only RMP 1 is functional. The Flight Deck Voice Recorder (CVR) and Digital Flight Data Recorder (DFDR) operate on the ground for $5\,minutes$ after power-up or whenever an engine is running. The CVR can be erased on the ground if the parking brake is set. The loudspeaker volume knob does not control the volume of aural alerts or voice messages. A white SEL light on the RMP indicates that a transceiver associated with that RMP is being tuned by a different RMP.

Normal Operating Procedures and Limitations

During cockpit preparation, batteries must show a minimum of $25.5\,volts$; if lower, a $20\,minute$ charge via external power is required. Battery charging current should be less than $60\,amps$ and decreasing within $10\,seconds$ of being set to AUTO. ADIRS fast alignment is performed if ground speed exceeds $5\,kts$. After engine start with the parking brake OFF, depressing the pedals should result in $0\,pressure$ on the indicators. T.O. INHIBIT suppresses low-priority alerts from $80\,kts$ until thrust reduction altitude or $2\,minutes$ after lift-off. LDG INHIBIT occurs below $800\,feet\,RA$. A flex thrust takeoff is prohibited on contaminated runways, defined as having $1/8\,inch$ of standing water.