Emergency Electrical Configuration: When the A320/A321 Loses Its Main Power

Imagine losing both engine generators simultaneously during flight. Your cockpit displays begin shutting down, automation disappears, and you're suddenly flying a very different aircraft. This is the Emergency Electrical Configuration (EMER ELEC CONFIG)—one of the most challenging scenarios you'll face as a pilot. Understanding how your aircraft responds and what systems remain available can differentiate between a manageable emergency and a catastrophic situation.

How the Emergency Electrical System Works

The EMER ELEC CONFIG automatically activates when AC BUS 1 and 2 lose power. This triggers a carefully staged sequence to keep you flying with essential systems powered. Close to 8 s, the Ram Air Turbine (RAT) deploys automatically, using airstream energy to drive the blue hydraulic system. This hydraulic pressure powers an emergency generator that produces 5 KVA of electrical power—enough for critical flight systems but far less than the 90 KVA each engine generator typically provides.

The emergency generator supplies power to the AC and DC ESS BUS through the essential transformer rectifier. This configuration maintains power to your most critical systems: Primary Flight Display (PFD) 1, basic flight controls in alternate law, essential navigation equipment, and primary communication radios. However, approximately 75 % of your aircraft's electrical equipment is automatically shed to preserve power for these vital systems.

Understanding the power hierarchy is crucial: The emergency generator takes priority over battery power when airspeed exceeds 100 kt, and the RAT functions properly. If the RAT stalls or you're below 100 kt, the system seamlessly transitions to battery power through the static inverter, giving you approximately 22 min of flight time once on batteries alone.

Managing Power Distribution and Speed Limitations

The system's logic revolves around maintaining minimum airspeeds to ensure power generation. At an airspeed of 140 kt, sufficient airflow is available to prevent any RAT from stalling and generate adequate power for the emergency generator. Below this speed (for some RAT types, 125 kt), you're relying solely on battery power with its 22-minute limitation. This explains why approach speeds become critical—maintaining 140 kt isn't just recommended; it's essential for continued electrical power.

When you lower the landing gear, the emergency generator automatically stops operating (on some aircraft types), and the system switches entirely to battery power. This design prevents hydraulic conflicts but creates a critical time limitation. You have approximately 22 min of battery power from gear extension to touchdown. The AC SHED ESS and DC SHED ESS buses are automatically disconnected to conserve power for essential systems.

As your speed decreases during landing, the system continues shedding non-essential equipment. Below 100 kt, the DC BAT BUS automatically connects to extend battery life. Even the AC ESS BUS is deactivated below 50 kt during the landing roll, causing all display units to shut down. This isn't a malfunction—it's the system preserving every possible amp of battery power.

When Things Go Wrong: System Failures and Responses

If the RAT stalls due to icing, damage, or insufficient airspeed, the emergency generator stops producing power. The system immediately transitions to battery backup, with the static inverter providing AC power to essential systems. The same automatic load shedding occurs—AC SHED ESS and DC SHED ESS buses disconnect, and the speed-based power management continues as described above.

Starting the APU can restore significant electrical capability, but each start attempt consumes approximately 3.5 min of battery life. If both engine generators have failed, avoid unnecessary APU start attempts unless you're confident of success. The APU generator can restore normal electrical configuration beyond the essential buses, but the emergency generator continues operating even after the APU starts, providing additional redundancy.

Critical decision point: If you're experiencing smoke or fumes of unknown origin, the EMER ELEC CONFIG can help isolate the problem by disconnecting most electrical equipment. However, this should be a deliberate decision based on the situation, not an automatic response to every electrical anomaly.

What This Means for Your Operations

Flying in EMER ELEC CONFIG fundamentally changes your aircraft's capabilities and operational procedures. Only PFD1 remains functional, making the left-seat pilot the designated pilot flying regardless of normal crew roles. The aircraft operates in alternate law with no autopilot, flight director, or autothrust available. When the landing gear extends, you'll be in direct law with significantly reduced flight envelope protections.

Navigation capabilities remain surprisingly robust: ND1, FMGC1, VOR1/ILS1, and DME1 continue operating. You can navigate precisely and fly instrument approaches, though you’ll need to manually tune the NAVAIDs in some aircraft using RMP1. Communication remains available through RMP1, RMP2 (e.g., neo aircraft), VHF1, HF1, and ATC1, ensuring you can coordinate with controllers and declare your emergency.

Critical systems lost may include one FAC, FMGC1 ILS tuning capability, BSCU (nose wheel steering and anti-skid), thrust reversers, and radio altimeters. The pilot monitoring must handle callouts for these lost systems. Alternate braking relies on yellow hydraulic pressure, modulated up to 1000 PSI, but without anti-skid protection.

Approach and landing considerations for some aircraft types include delaying landing gear extension until 1000 ft to maximize emergency generator operating time. Tune navigation aids in advance since you'll lose some automatic tuning capabilities. Maintain at least 140 kt on approach to keep the emergency generator operating—plan for manual braking with limited accumulator pressure and no anti-skid system.

The EMER ELEC CONFIG represents your aircraft's determination to keep you flying when major electrical failures occur. While it significantly reduces your aircraft's capabilities, understanding these limitations and the system's logic helps you manage the emergency effectively. Remember that this configuration isn't designed for extended flight—land as soon as practical at a suitable airport with adequate emergency services, avoiding marginal weather conditions even if ECAM displays "LAND ASAP" in red. Your aircraft will get you down safely, but success depends on understanding the available systems and how to use them effectively in this degraded configuration.

What remains when the A320 loses both generators – how the RAT, emergency generator, and battery power work, and what pilots need to know to land safely.