A320 Emergency Electrical Configuration

The A320's emergency electrical configuration (EMER ELEC, shown on the ECAM as ELEC EMER CONFIG) is what is left when AC BUS 1 and AC BUS 2 have both lost their supply. Above 100 kt the ram air turbine (RAT) extends into the airflow and pressurizes the blue hydraulic system, which drives a small emergency generator. Until it couples, and whenever it cannot run, the two batteries and a static inverter carry the load. Only the essential buses stay powered, so the crew fly with the captain's instruments and one VHF radio, and without the protections of normal law.

Each of the three generators can supply all the bus bars on its own, so all three must be unavailable at once, but it does happen: Airbus and the NTSB have both reported cases. The network itself is described in A320 electrical system; this article follows what happens when it fails and how crews get out of it.

Loss of main AC generation

The generators are never connected in parallel. Engine generators 1 and 2 each feed their own AC bus, and bus tie contactors let the APU generator, external power or the other engine generator take over a bus that has lost its source. Both main AC buses go dead only when no source remains for either:

• Both integrated drive generators (IDGs) fail. Worn components inside the IDGs' constant speed drives can upset frequency regulation, and Airbus has had reports of both IDGs failing in sequence for that reason (see the reported events below). In the Spirit Airlines event investigated by the NTSB, generator 2 tripped at normal load and generator 1 after its load had doubled.
• Both engines fail. The NTSB notes that an IDG supplies power only above about 54 % N2, so the generators drop off as the engines run down. Without the APU generator, the aircraft goes into the emergency configuration; the ENG DUAL FAILURE warning comes with both GEN FAULT lights.
• The electrical smoke procedure sheds the main busbars deliberately. Its distribution is that of the emergency configuration, except that the fuel pumps are connected upstream of the GEN 1 line contactor, so that GEN 1 keeps feeding them.
• On the ground, the same Spirit Airlines A319 lost electrical power three times in January 2020 during single-engine taxi after landing, with one IDG carrying the whole electrical load (NTSB).

RAT extension and the emergency generator

With the MAN ON pushbutton at AUTO, the RAT extends automatically when AC BUS 1 and AC BUS 2 are both lost and the speed is above 100 kt. The crew can extend it at any time with the guarded MAN ON pushbutton on the EMER ELEC PWR panel; a RAT MAN ON pushbutton on the hydraulic panel also extends it to pressurize the blue system. The RAT is a drop-out turbine, stowed in the left belly fairing, coupled to a hydraulic pump on the blue system, which then works at 2,500 psi instead of the normal 3,000 psi. Once extended, it can be stowed only on the ground.

The blue system drives the constant speed motor/generator (CSM/G), the emergency generator, through a hydraulic motor. It delivers 5 kVA of three-phase 115/200 V, 400 Hz power. Its own generator control unit controls the start-up, keeps it at constant speed, regulates its voltage and protects the network through its line contactor; it is never synchronized with another source. After an automatic extension the generator couples about 8 seconds after the loss of the main buses; after a manual extension it couples 3 seconds after the RAT starts supplying it.

The indications follow the sequence:

• the red RAT & EMER GEN FAULT light on the EMER ELEC PWR panel comes on whenever the emergency generator is not supplying power while AC BUS 1 and 2 are unpowered;
• the ECAM shows the green EMER GEN memo once the generator runs, and the green RAT OUT memo while the RAT is not stowed;
• on the ELEC page AC BUS 1 and 2 are amber, and the emergency generator's voltage and frequency turn amber outside 110 to 120 V and 390 to 410 Hz; they are not shown while its line contactor is open;
• on the HYD page RAT appears in green when the RAT is out, and with an amber arrow if its pump is not available.

The guarded EMER GEN TEST pushbutton, held with the normal AC buses supplied, drives the emergency generator from the blue electric pump and connects the AC ESS and DC ESS buses, but not the shed buses, to it; on the ground the ELEC page appears automatically. Held with only the batteries supplying the aircraft, it lets the static inverter power the AC ESS bus.

Buses still powered

With the emergency generator running, the AC ESS FEED pushbutton no longer matters, and the essential transformer rectifier (ESS TR), unused in normal flight, turns the generator's output into DC for the DC ESS and DC SHED ESS buses. The essential loads, among them the captain's PFD and ND, key avionics and key lighting, sit on these buses; galleys, the DC entertainment bus and most cabin lighting are shed.

Batteries-only configuration

The batteries carry the emergency network on their own in four cases: during the roughly 8 seconds before the emergency generator couples, if the RAT stalls, if the emergency generator fails, and on the ground below 100 kt, when the RAT no longer drives it. Then:

• BAT 1 drives the static inverter, which turns its DC into 1 kVA of single-phase 115 V, 400 Hz AC for part of the AC ESS bus. Above 50 kt it runs automatically, whatever the BAT pushbutton positions; below 50 kt only if both BAT pushbuttons are on.
• BAT 2 supplies the DC ESS bus.
• The AC SHED ESS and DC SHED ESS buses are shed to save the batteries, and SHED appears against them on the ELEC page.

The AC ESS FEED FAULT light stays out while the static inverter feeds the AC ESS bus, because that bus is still supplied; if the static inverter itself has failed, the AC ESS bus is lost. Some loads switch over by themselves: once the static inverter is operating, igniter A of each engine moves to the static inverter bus, and the APU fuel pump runs from that bus if the AC SHED ESS bus has failed. On the flight deck only the right-hand dome light remains.

Each battery has a normal capacity of 23 Ah. The time they can carry the emergency network is given in the FCOM for the aircraft concerned.

Worked example: both generators lost in descent at 250 kt

1. GEN 2 fails, the APU is not running, and GEN 1 takes over both AC buses. Shortly afterward GEN 1 fails too: AC BUS 1 and 2 are lost.
2. The batteries take the essential network at once: BAT 1 through the static inverter for the AC ESS bus, BAT 2 for the DC ESS bus. The shed buses go dark.
3. Being above 100 kt, the RAT extends and blue pressure builds to 2,500 psi.
4. About 8 seconds after the loss, the emergency generator couples and takes the AC ESS and AC SHED ESS buses, and through the ESS TR the DC ESS and DC SHED ESS buses; the EMER GEN memo appears.
5. If the RAT were to stall, the network would fall back to step 2 and the shed buses would be lost again.

Effects on systems and flight controls

Without a main generator the flight controls leave normal law. The NTSB found that, had the captain of US Airways Flight 1549 not started the APU, the airplane would not have remained in normal law with its flight envelope protections. In the reconfiguration laws the protections are reduced or lost, and alpha floor is inoperative in both alternate and direct law (see A320 flight control laws and protections). The green and yellow hydraulic systems keep their engine-driven pumps as long as the engines run.

ECAM procedure and recovery

The ECAM alert is ELEC EMER CONFIG, and while it is active secondary failures are inhibited on the ECAM. Getting out of the configuration means getting a main source back; the FCOM procedure gives the exact sequence, and the means are these:

• Reset the generators. Selecting a GEN pushbutton OFF opens the generator line contactor and resets the fault circuit; back at ON, the line contactor closes if the generator's parameters are normal. After a differential fault, a reset has no effect after two attempts. Airbus's Safety First article also gives crews recommendations for avoiding the emergency configuration after a single generator failure.
• Start the APU. It can be started from the batteries or from the normal network, and starting it is permitted throughout the normal flight envelope; the US Airways Engine Dual Failure checklist quoted by the NTSB placed the APU start after the relight attempts, below FL 250. During the start the batteries are connected to the DC BAT BUS while the MASTER SW is on and APU speed is below 95 %; with the emergency generator running, that connection is limited to 3 minutes. Once on line, the APU generator can replace both engine generators.
• Reset FAC 1. In the US Airways Engine Dual Failure checklist quoted by the NTSB, turning FAC 1 off then on recovers the characteristic speeds on the PFD and permits recovery of the rudder trim even if no indication is available.

The same checklist told the crew to turn on emergency electrical power, that is, to extend the RAT manually with MAN ON, if the emergency generator was not on line.

The FAA's Flight Standardization Board report makes "total loss of electrical power, emergency electrical configuration" a flight maneuver for pilots converting from the A330 or the A340: it is trained at Level D, in a device that flies it in real time, and needs no separate check (Level A). This article follows the A320 FCOM as quoted in the v1prep question banks, which draw no ceo/neo distinction here; the A321neo XLR, which has no FACs, reconfigures its flight controls differently.

Reported events

Worn IDGs (Airbus, 2025). Airbus's Safety First article on preventing the loss of engine generators, as summarized on its web page, reports cases of emergency electrical configuration on A320 aircraft in which both IDGs failed in sequence because of worn components inside their constant speed drives. The article describes one of these events, explains why worn IDGs may have frequency regulation problems in certain circumstances, presents the preventive maintenance tasks introduced to detect worn IDGs in advance, and gives flight crews recommendations for preventing the emergency configuration after a single generator failure.

Spirit Airlines A319, Sacramento (NTSB, 2020). On 15 February 2020, Spirit Airlines Flight 1818, an Airbus A319-132 registered N521NK, was descending from 4,000 to 2,000 ft on approach to Sacramento when the crew saw ELEC GEN 2 FAULT and, about 11 seconds later, ELEC GEN 1 FAULT. AC BUS 1 and AC BUS 2 lost power, several flight deck displays and systems went with them, and the RAT extended automatically and drove the emergency generator. The crew declared an emergency and landed without further incident; none of the 117 occupants was injured. The aircraft had lost both generators on approach to Atlanta the day before. The NTSB found that a fixed cylinder block in each IDG had significant wear of its reworked brass liners, which made the IDGs' output frequency go outside its design limit.

Hudson River ditching (NTSB, 2009). On 15 January 2009 both engines of US Airways Flight 1549, an A320, lost thrust after the airplane struck a flock of birds, and the captain started the APU at once, an item the crew never reached in the checklist. The NTSB concluded that this ensured a primary source of electrical power and kept the airplane in normal law, with its flight envelope protections, before the ditching on the Hudson River; the RAT was found extended after the aircraft was recovered from the water (see forced landing and ditching).

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.