Every flight depends on a continuous supply of electrical power—from the displays showing critical flight information to the computers managing your aircraft's systems. But what happens when generators fail? How does the A320/A321 ensure you always have electricity for essential systems? The electrical system solves this challenge through multiple layers of redundancy and intelligent power management that automatically prioritizes the most critical systems when power sources are lost.

How the Electrical System Works

Your aircraft operates on a dual-voltage electrical architecture: a primary 115/200 V AC system at 400 Hz constant frequency, with a secondary 28 V DC system derived from the AC power. Think of this like a city's power grid—AC power is the main transmission system, while DC power serves specific neighborhoods with specialized needs.

The Power Hierarchy

The system follows a strict priority order that ensures the most reliable sources always take precedence:

1. Engine generators (GEN 1 and GEN 2)—highest priority

2. External ground power—when connected and selected ON

3. APU generator—backup power source

4. Emergency generator—last resort for essential systems

Each engine-driven generator produces 90 KVA through an Integrated Drive Generator (IDG), providing enough power to run the entire aircraft. The APU generator can also power the complete electrical network, making it invaluable during ground operations and as an in-flight backup.

Normal Power Distribution

During normal flight operations, each engine generator powers its respective AC bus (AC BUS 1 and AC BUS 2) through generator line contactors. AC BUS 1 typically supplies the AC essential bus, which feeds the most critical systems. Transformer rectifiers convert AC power to DC, with TR 1 powering DC BUS 1, the DC battery bus, and the DC essential bus, while TR 2 handles DC BUS 2.

Managing Power Distribution

The system's intelligence lies in its Bus Tie Contactors (BTCs)—these smart switches automatically reroute power when needed. During single-engine operations or when powered by the APU or external power, both BTCs close to ensure power reaches all systems. When both engines run normally, the BTCs open, allowing each generator to power its side independently.

Automatic Load Management

When power becomes limited, the system automatically sheds non-essential loads to protect critical systems. Galley power, secondary galley systems, in-seat power, and entertainment systems are the first to go. This happens automatically in flight when only one generator operates, or on the ground when only one engine generator is running. The system is smart enough to keep all galley systems available if powered by the APU generator or external power, recognizing these sources have sufficient capacity.

Battery Operations

Your two 23 Ah batteries serve multiple roles beyond emergency backup. They're always connected to the hot buses, providing power for systems that must remain active even when the aircraft is completely shut down. During normal operations, batteries charge automatically when voltage drops below 26.5 V, with charging stopping when the current falls below 4 A. The system includes automatic cut-off logic to prevent battery depletion on the ground—if external power and generators are off and battery voltage is low, the contactors open to preserve the remaining battery power.

When Things Go Wrong

Single Generator Failure

When one engine generator fails, the system seamlessly transitions to either the APU generator (if available) or the remaining engine generator. Bus tie contactors automatically close to distribute power across both sides of the aircraft. You'll notice automatic galley load shedding as the system prioritizes essential systems over passenger comfort.

Total AC Power Loss—Emergency Electrical Configuration

This is where the system's emergency design becomes critical. When both AC BUS 1 and AC BUS 2 lose power above 100 kt, the Ram Air Turbine (RAT) automatically deploys. The RAT drives the blue hydraulic system, which powers the emergency generator, producing 5 KVA—enough for essential flight instruments and controls but not passenger systems.

The emergency generator powers the AC and DC essential buses, giving you Primary Flight Display (PFD) 1, basic engine parameters, and essential flight controls. However, you lose the autopilot, flight directors, autothrust, and most secondary systems. Only the left-seat pilot has a functioning display, making them the designated pilot flying.

Critical Speed Considerations

For some aircraft, the 140-knot minimum approach speed isn't arbitrary—it's the minimum speed needed to keep the RAT spinning fast enough to generate emergency power. Below this speed, you're relying solely on battery power with approximately 22 min available. On other aircraft variants, when the landing gear extends, the emergency generator stops, and you transition to battery-only power, making time management crucial.

Ground Operations and Low Speed

Below 100 kt, the DC battery bus automatically connects to provide power. Below 50 kt, the AC essential bus sheds, causing all display units to shut down during the landing roll. This explains why you must complete all essential actions before reaching these critical speeds.

What This Means for You

Operational Decision Making

Understanding the electrical system helps you make better decisions during abnormalities. When you see "LAND ASAP" in red after losing both generators, you know you have limited battery power once the gear extends on some aircraft. This knowledge helps you choose appropriate airports—avoid poorly equipped fields or marginal weather when your systems are degraded.

System Monitoring

When the generator control unit trips, differential faults occur, or line contactors open unexpectedly, the FAULT lights on the generator switches illuminate. These aren't just status lights—they're telling you about the health of your power generation system and helping you anticipate potential issues.

Emergency Procedures

In smoke situations, the electrical system can be configured to emergency mode to isolate potential sources. Understanding that this sheds about 75 % of electrical equipment helps you recognize why specific systems become unavailable and why you might need to restore normal electrical configuration before landing for systems like normal braking.

Maintenance Considerations

The IDG disconnect switches are guarded and spring-loaded because disconnection requires maintenance to reconnect. Never hold the switch longer than 3 s to avoid damaging the disconnection mechanism, and only disconnect when the engine is running or windmilling to prevent starter damage.

The electrical system's design philosophy centers on redundancy and automatic management, allowing you to focus on flying the aircraft while the system handles power distribution priorities. Understanding how these systems work together enables you to better anticipate system behavior during abnormal situations and make informed decisions about continuing flight or diverting when electrical problems arise.

From generators to the RAT, the A320’s electrical network ensures critical systems stay alive when power sources fail.