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Chapter 4. Electrical

Table of Contents

4.1. Emergency configuration
4.2. Battery only
4.3. IDG low oil pressure/ high oil temperature
4.4. Generator fault
4.5. Battery fault
4.6. AC Bus 1 fault
4.7. AC Bus 2 fault
4.8. AC Ess Bus fault
4.9. AC Essential Shed Bus lost
4.10. DC Bus 1 fault
4.11. DC Bus 2 fault
4.12. DC Essential Bus fault
4.13. DC Essential shed
4.14. Loss of DC Bus 1 and DC Bus 2
4.15. Generator overload
4.16. Loss of TRs
4.17. Battery bus fault
4.18. DC Emergency configuration
4.19. Static inverter fault
4.20. Generator 1 line off
4.21. Tripped circuit breakers

4.1. Emergency configuration

Attempt to restore normal power by recycling the main generators. If that fails, try again after splitting the systems with the BUS TIE button.

If normal power cannot be restored, ensure that the emergency generator is on line (deploy the RAT manually if required) and maintain speed >140kt to avoid RAT stall. Cycling FAC 1 will recover rudder trim. Once 45 seconds have elapsed and when below FL250, the APU can be started.

So much equipment is lost in the emergency configuration that QRH AEP.ELEC provides a table of surviving equipment. Notable losses are:

  • All the fuel pumps, requiring Gravity Fuel Feeding procedures to be used (see Section 7.4, “Gravity fuel feeding”) and making center tank fuel unusable.

  • The anti-skid, three fifths of the spoilers and the reversers. Combined with the higher landing speeds required to prevent RAT stall this results in significantly increased landing distances.

  • Alternate Law with reduced protections. Mechanical yaw becoming Alternate Law yaw with FAC1 reset. Anticipate Direct Law at gear extension and be prepared for a Direct Law go around. Manual pitch trim is available.

  • Anti-icing for probes supplying the standby instruments: in case of disagreement, go with the CM1 instruments.

  • Nose Wheel Steering. Use differential braking to clear the runway.

QRH AEP.ELEC also provides a paper summary which should be applied once ECAM actions are complete.


4.2. Battery only

Power is available for approximately 30 minutes.[17] QRH AEP.ELEC provides details of remaining equipment. This is very similar to the emergency electrical configuration (see Section 4.1, “Emergency configuration”) with the additional loss of FAC1 and FMGC1. An attempt should be made to bring the emergency generator on line by ensuring speed is >140kt and deploying the RAT with the EMER ELEC PWR MAN ON button.


4.3. IDG low oil pressure/ high oil temperature

The IDG should be disconnected. Assuming the associated engine is running, press the IDG button until the GEN FAULT light comes on. Do not press the button for more than 3 seconds.

The APU generator should be used if available.


4.4. Generator fault

Try to reset the generator by turning it off, then after a short pause, turning it on again. If unsuccessful, turn it back off.

If an engine driven generator cannot be recovered, the APU generator should be used if available.

Single generator operation leads to shedding of the galley. Loss of an engine driven generator leads to loss of CAT III DUAL capability.


4.5. Battery fault

The affected battery contactor opens automatically. APU battery start is unavailable with a single battery.


4.6. AC Bus 1 fault

Some or all of the equipment on AC bus 1 becomes unavailable, including TR1. DC Bus 1 is powered from DC Bus 2 via the battery bus. Power must be re-routed to the Essential AC bus via AC bus 2. This is automatic on some aircraft. Manual re-routing is achieved with the AC ESS FEED button. Once Essential AC is powered, the Essential TR powers the DC Essential bus.

Notable lost equipment includes the blue hydraulic system and associated services (including spoiler 3), radio altimeter 1 (and hence Cat III capability), half the fuel pumps, the nose wheel steering, the avionics blower fan and p1 windshield heat.


4.7. AC Bus 2 fault

Some or all of the equipment on AC bus 2 becomes unavailable, including TR2. DC bus 2 is powered from DC bus 1 via the battery bus. The majority of this equipment has a redundant backup, the loss of the FO’s PFD and ND and a downgrade to Cat I being the major issue. Landing distances are unchanged.


4.8. AC Ess Bus fault

It may be possible to recover the bus by transferring its power source to AC BUS 2 with the AC ESS FEED button. If this is unsuccessful, some or all of the equipment on the AC ESS bus will be lost. The majority of this equipment has a redundant backup, with the loss of the Captain’s PFD and ND and a downgrade to Cat I being the major issues. Landing distances are unchanged.

It is worth noting that loss of AC Ess Bus implies loss of Passenger Oxygen masks. Where appropriate, this loss of redundancy can be mitigated by flying at a level where descent to a safe altitude can be achieved without masks. The main form of guidance on altitude hypoxia comes in the form of “Time of useful consciousness” tables. Working on the principal that if you remain conscious you definitely remain alive, 25,000ft would seem to be a good compromise. This gives you 2 to 3 minutes of useful consciousness to dive to 18,000ft, where you would then have 30 minutes to clear any terrain.[18]


4.9. AC Essential Shed Bus lost

Some or all of the equipment on the AC ESS SHED bus is lost. The major issue is the loss of the passenger oxygen masks. Landing distances are unchanged.


4.10. DC Bus 1 fault

Some or all of the equipment on DC Bus 1 is lost. Most of the equipment loss causes loss of redundancy only. Landing distances are unchanged.


4.11. DC Bus 2 fault

Some or all of the equipment on DC Bus 2 is lost. The F/O’s static probe sensor is lost, so ADR3 should be selected on the F/O’s side. FCU2 is lost, so check that the baro ref on the FCU and PFD agree. Landing distance increases by up to 35% due to the loss of 3 ground spoilers per side and one reverser. Autobrake is also unavailable. Due to the loss of SFCC2, the slats and flaps will be slow and the engines will remain in approach idle. FAC2 is lost, so the characteristic speeds on both PFDs are provided by FAC1. F/O window heat, wipers and rain repellent are lost.

The other lost systems either have redundant backups or are non-essential. It should be noted that the only flight computers remaining are ELAC 1, SEC 1 and FAC 1.


4.12. DC Essential Bus fault

The major headache associated with DC Essential Bus failure is significant loss of communications systems. This is exacerbated by a design flaw which, at time of writing, affects MSNs 2037–2402 and MSNs 2471–3122. By design, ACP1 and ACP2 are lost, along with VHF1. This allows two-way communication to be recovered by one pilot using ACP3 (selected via the AUDIO SWTG rotary selector) with VHF2 or VHF3. Since speaker 1 is also lost, having P2 handle the radios with speaker 2 at high volume is the only method of both pilots having awareness of ATC communications. On the MSNs detailed above, however, the audio cards connecting cockpit mikes and headsets are all powered from the DC Essential Bus. It may be possible to receive transmissions with a combination of VHF2/3, ACP3 on FO and speaker 2 on, but transmission is limited to morse code on the transmit switch[19].

FCU1 is lost, so the baro refs should be checked. The GPWS is lost and should be turned off.

Landing distances are increased due to the loss of reverser 2 and the loss of the blue hydraulic system (and hence spoiler 3). Wing anti-ice is also lost, so landing distances will also increase significantly if ice is accreted and increased approach speeds are required.

Slats and flaps are slow due to the loss of SFCC1. This also leads to the engines reverting to approach idle.

Landing capability is Cat 2 due to the loss of the auto-thrust. The ECAM status page incorrectly reports Cat 3 single.

The FCOM lists additional systems beyond those listed on the STATUS page that are lost with DC Essential Bus failure. Of note among these is loss of HP fuel shutoff valves. This requires that the engines are shut down with the Engine Fire pushbutton switches.


4.13. DC Essential shed

The only major issue is the loss of wing anti-ice. Therefore, avoid icing conditions, and apply landing distance procedure if ice accretes.


4.14. Loss of DC Bus 1 and DC Bus 2

Some or all of the systems supplied by DC Bus 1 and DC Bus 2 are lost.

The implications are the same as for Section 4.18, “DC Emergency configuration” except that the RAT will not need to be deployed since ESS TR will be supplied from AC 1 instead of the emergency generator.


4.15. Generator overload

Shed some load by switching off the galleys.


4.16. Loss of TRs

No systems are lost as a result of failure of a single TR. If the fault is with TR1 or TR2, DC ESS will be supplied by the ESS TR via AC ESS; in this case only Cat 3 single will be available.

If TR1 and TR2 are both lost then DC Bus 1, DC Bus 2 and the DC Battery Bus will also be lost. DC ESS will remain powered by the ESS TR. The FCOM is not very forthcoming regarding this failure; there is only a description in the DSC section and nothing specific in the PRO section. The situation is, however, very similar to the “ECAM complete” phase of Section 4.18, “DC Emergency configuration”; the only difference is that AC 1 rather than the emergency generator is providing the power to the ESS TR, and hence you don’t need to worry about RAT deployment or RAT stall.


4.17. Battery bus fault

Some or all of the equipment on the Battery bus is lost. The only major items lost are APU fire detection and APU battery start.


4.18. DC Emergency configuration

Defined as the loss of DC BUSSES 1 + 2, DC ESS BUS and DC BAT BUS. Recovery assumes that the DC ESS BUS can be fully restored by deploying the RAT with the EMER ELEC PWR button.

Equipment powered or controlled through DC BUS 1, DC BUS 2 and the BAT BUS is lost. Loss of the equipment associated with the BAT BUS is fairly benign: mainly APU Battery Start is unavailable due to loss of the APU ECB and APU fire detection is inop. A lot of equipment is lost with the loss of DC BUS 1+2, but it is worth remembering that all three busses are also lost in Emergency Electrical Config, so you will have, at minimum, all the equipment detailed in QRH 24.1. The main items of note are:

  • A long runway is required. Minimum VAPP is 140kt to prevent RAT stall. Antiskid, reversers and 60% of the spoilers are lost. Loss of nosewheel steering adds to the difficulty. Braking is from the ABCU, so only manual braking is available.[20]

  • Flight computer redundancy is significantly reduced, with only ELAC 1, SEC 1 and FAC 1 available. This is, however, sufficient to keep Normal Law, so a CONF FULL landing and, indeed, CAT 3 SINGLE autoland (using AP1 and FMGS1) are available. The latter may be useful since wipers and window heat are lost. Only FCU 1 is available.

  • Deployment of lift devices is slow due do loss of SFCC 2, but they are all available. Normal gear operation is available through LGCIU 1.

  • Pressurised fuel is available from the #1 wing tank pumps, but center tank fuel is unusable.

  • Redundancy in the pressurisation system is seriously compromised. Manual pressure control and CPC 2 are lost, so you are reliant on CPC 1 for control. Pack 2, BMC 2 and cross bleed control are all lost, so you are reliant on ENG 1 Bleed and Pack 1 for supply. Ram Air remains available, so if required a slow depressurisation through turning off Pack 1 followed by a depressurised landing with Ram Air is achievable.

  • Communications are limited to VHF 1, controlled by RMP 1.

  • Redundancy in the fire detection and suppression systems is compromised. The engines each retain one detection loop and one fire bottle. APU fire detection and cargo fire extinguishing are lost.

  • Heating for all static ports is lost, so be alert for unreliable airspeed and altitude.


4.19. Static inverter fault

Normal operations are not affected.


4.20. Generator 1 line off

Pressing the GEN 1 LINE button on the emergency electrical panel has much the same effect as pressing the GEN 1 button on the main electrical panel, with the difference that GEN 1 continues to supply its associated fuel pumps. It is primarily used for the smoke drill. If it’s not meant to be off, turn it on.


4.21. Tripped circuit breakers

It is generally not recommended to reset circuit breakers in flight. It is, however, acceptable to attempt a single reset if it is judged necessary for the safe continuation of the flight.

On the ground, any circuit breakers other than those for the fuel pumps may be reset as long as the action is coordinated with MOC.

The ECAM warning will be triggered if a green circuit breaker trips.


[17] This information was part of Airbus CBT training. There is no figure available in the FCOM.

[18] These tables are obviously not designed to be used in this way – the exposure to hypoxia in the descent will likely impact the TOUC at 18,000ft, and we are really more concerned with survivability than useful consciousness – but they can at least give a feeling for the parameters involved.

[19] I am only inferring this solution from the list of equipment lost; there is no specific documentation to indicate that it will work.

[20] easyJet aircraft automatically modulate to 1000psi, but the sim may not.