If there is any conflicting information, your FCOM shall be the overriding reference.

Q1. There are four sources of AC power: GEN1, GEN2, APU GEN, & EXT PWR.

What is the normal priority of supply for AC BUS1?

A1. The normal priority of supply for AC BUS 1 is :-

(i) GEN 1

(ii) EXT PWR

(iii) APU GEN

(iv) GEN 2

Q2. After no 2 engine start, which generator is powering AC BUS 1?

{Consider APU GEN on- line.}


Q3. In flight, GEN 1 has failed and there is no APU. Which generator is powering AC Bus 1?

A3. GEN 2is powering AC BUS 1. There is automatic shedding of part of the galley load.

Q4. Name the different AC bus bars?

A4. The different AC BUS BARS are :-

(a) AC BUS 1

(b) AC BUS 2






Q5. Name the different DC Bus bars?

A5. The different DC BUS BARS are :-

(a) DC BUS 1

(b) DC BUS 2



(e) HOT BUS 1

(f) HOT BUS 2




Q6. What is TR?

A6. TR is short for Transformer Rectifier. A TR unit is used to convert AC into relatively smooth DC. Independently :-

(a) Transformer : A Transformer changes the AC voltage source, be it from a generator or power line, to a different voltage for any number of applications.

(b) Rectifier : A Rectifier changes AC electricity, which travels in two directions, to DC using components called diodes, which only pass the electricity in one direction.

Q7. Normally, how the TRs supply the electrical network?

A7. In normal configuration :

(a) TR 1 normally supplies DC BUS 1, DC BAT BUS and DC ESS BUS.

(b) TR 2 normally supplies DC BUS 2.

Q8. If in a flight, both TR1 & TR2 are lost, which buses are lost?

A8. If TR 1 and TR 2 are lost; DC BUS 1, DC BUS 2 and DC BAT BUS are lost. The DC ESS BUS is supplied by the ESS TR.

Q9. Normally, ESS TR does not supply a/c electrical network. True or False?


Q10. Name any three abnormal / emergency conditions in which ESS TR is supplying DC ESS Bus?

A10. In the following conditions, the ESS TR is supplying the DC ESS BUS :-

(a) AC BUS 1 failure.

(b) Single TR failure.

(c) Double TR failure.

Q11. What is the function of static inverter? And to which BUS will it supply?

A11. A Static Inverter transforms DC Power from Battery 1 in to One KVA of single phase 115 Volt 400 Hertz AC power, which is then supplied to part of the AC ESS BUS. When the aircraft speed is above 50 knots, the inverter is automatically activated, if nothing but the batteries are supplying electrical power to the aircraft, regardless of the BAT 1 and BAT 2 P/b positions.

When the aircraft speed is below 50 knots, the inverter is activated, if nothing but the batteries are supplying electrical power to the aircraft, and the BAT 1 and BAT 2 P/b’s are both on at AUTO.

The STAT INV supplies partly to the AC ESS BUS.

Q12. What does the amber FAULT light in BAT P/B indicate?

A12. The FAULT Lt. comes on AMBER in the BAT P/b, accompanied by an ECAM caution, when the charging current for the corresponding battery is outside limits. In this case, the battery contactor opens.

Q13. If the BAT pushbuttons are in AUTO position overnight without any other power, will the batteries discharge completely?

A13. No, the batteries will not discharge completely. A Battery Automatic cut-off logic prevents the batteries from discharging completely when the aircraft is on the groung (Parking).

Automatic battery contactors open when :-

–The a/c is on the gorund.

–The BAT P/b s/w’s are at AUTO

–The main power supply (EXT PWR+GEN) is cut off

–Battery Voltage is low.

Q14. If automatic cutoff has occurred, how can the crew re-establish battery power?

A14. The flight crew can reset the contactors by switching the BAT P/b switch to OFF and then to AUTO.

Q15. If the battery switches are at AUTO, when will batteries be connected to the DC BAT BUS?

A15. The batteries are connected to the DC BAT BUS in the following cases :-

(a) APU starting (MASTER SW at ON & N< 95%).

Note : The conn. is limited to 3 mins when the emergency generator is running.

(b) Battery voltage below 26.5 V (Battery Charge). The charging cycle ends when battery charge current goes below 4 Amps.

–On ground, immediately

–In flight, after a time delay of 30 minutes.

(c) Loss of AC BUS 1 and 2 when below 100 knots (EMERG. GEN not supplying).

Q16. Prior to the first flight of the day, what should the battery voltage be?

A16. 25.5 V.

Q17. During preflight, what options are available if the battery voltage for either battery is below 25.5 volts?

A17. If BAT voltage 25.5, a charging cycle of 20 minutes is required.

— BAT 1 & 2 . . . . . . . . . . . . . . . . . . . . . . . .AUTO

— EXT PWR. . . . . .. .. . . . . . . . . . . . . . . . . . . . ON

Check on ECAM ELEC page, battery contactor closed and batteries charging.

After 20 minutes,

— BAT 1+2 . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . OFF

— BAT 1+2 Voltage . . . . . . . . . . . . . . . . . .Check above 25.5

Q18. What is the meaning of green AVAIL light in EXT PWR p/b?

A18. AVAIL light in EXT PWR P/b comes on Green if :-

(a) External power is plugged in, and

(b) External power parameters are normal.

Q19. What is the meaning of blue ON light in EXT PWR p/b?

A19. The Blue light in EXT PWR P/b means that the external power line contactor is closed and thus, the external power is powering the aircraft’s electrical system.

Q20. If both engines are started at the gate using external electrical power, will blue ON light in EXT PWR p/b extinguish automatically after engine start?

A20. NO.

Q21. Can the APU generator power all the buses in flight?

A21. YES.

Q22. In flight, you get an ECAM, ELECT IDG1 OIL PR LO. As per the checklist, you have to disconnect IDG1. What are the cautions you will follow while disconnecting the IDG?

a) How will you know that IDG is disconnected?

b) In the above situations, how AC BUS 1 is powered?

c) Is Main Galley still powered in this situation?

d) Can you start APU and use its GEN in the above case?

e) Can this IDG be reconnected in flight if required?

A22. Cautions to follow while disconnecting the IDG :-

(i) If the associated engine is running, the IDG must be disconnected from the engine at or above idle to prevent damage to the disconnect mechanism.

(ii) Press the IDG P/b until the GEN FAULT Lt. comes on. However, do not press it for more than 3 seconds to avoid damage to the disengage solenoid.

(a) The IDG FAULT Lt. goes off when the IDG is disconnected.

On ECAM ELEC page.:

(i) IDG legend becomes Amber

(ii) DISC. legend appears in Amber.

(b) AC BUS 1 is powered by GEN 2.

(c) NO.

(d) YES.

(e) NO.

Q23. IDG label is normally displayed in white on ELECT page. Under what conditions, this turns into amber in color?

A23. The IDG label, normally white, becomes Amber if,

(a) Oil Outlet Temp. > 105 degrees centigrade.

(b) Oil Pressure gets too low.

(c) IDG becomes disconnected.

The 1 or 2 is white if the corresponding engine is running, Amber if it is not and the FADEC is powered.

Q24. What happens if GEN 2 also fails while GEN 1 is not available as its IDG is disconnected in flight? Consider APU not available.


If both main AC buses are lost with airspeed above 100 knots, what will happen?

A24. If AC BUS 1 and AC BUS 2 are lost and the aircraft speed is above 100 knots, the Ram Air Turbine (RAT) extends automatically. This powers the blue hydraulic system, which drives the emergency generator by means of a hydraulic motor. This generator supplies the AC ESS BUS & the DC ESS BUS via the ESS TR. If the RAT stalls, or if the aircraft is on the ground with a speed below 100 knots, the emergency generator has nothing to drive it. The emergency generation network automatically transfers to the batteries and static inverter, & the system automatically sheds the AC SHED ESS and DC SHED ESS busses.

Q25. What does the RAT & EMER GEN red FAULT light indicate when illuminated?

A25. When the ‘RAT & EMER GEN’ FAULT Lt. is illuminated Red, it means the emergency generator is not supplying power when the AC BUS 1 & AC BUS 2 are not powered.

Q26. What is the difference when you extend RAT manually from HYD panel and from EMER ELEC Panel?

A26. When the RAT is extended manually from the HYD panel, the RAT supplies only Blue system hydraulic pressure and no emergency electrical generation. Whereas, when extended manually from the EMER ELEC panel, it supplies emergency electrical power as well.

Q27. Which buses are supplied by EMER GEN?

A27. The following busses are supplied by EMER GEN :-

(a) AC ESS


(c) DC ESS


Q28. In case of ELECT EMER CONFIG, what are the important systems that are lost?




*ADR 2+3

*IR 2+3

*RA 1+2

*SPLR 1+2+5


*SEC 2+3


*AP 1+2





Q29. What is the main difference in ELECT EMER CONFIG due to failure of both AC BUS1 and AC BUS2 & ELECT EMER CONFIG due to smoke?

A29. The main difference is that the fuel pumps are connected upstream of the GEN 1 Line Connector.

Q30. What is the meaning of SMOKE light in the GEN 1 LINE p/b?

A30. The Amber SMOKE Lt. in the GEN 1 LINE P/b is triggered on when smoke is detected in the avionics ventilation duct.

Q31. If you put GEN 1 LINE p/b off, what happens? When do you have to switch off GEN1 LINE to OFF?

A31. When you put GEN 1 LINE P/b off, the GEN 1 line contactor opens. The AC BUS 1 channel is supplied from GEN 2 through bus tie contactors.

An electrical procedure is applied to eliminate the cause of the smoke if the smoke emission persists for more than 5 minutes.

–> EMER ELEC GEN 1 LINE . . . . . . . . . . . . . . . OFF

Q32. What is the normal source of power for AC ESS BUS?

A32. The AC ESS BUS is normally supplied from the AC BUS 1. It may be supplied by the AC BUS 2 through the AC ESS FEED P/b s/w.

Q33. What is the meaning of FAULT light in the AC ESS FEED p/b?

A33. The FAULT Lt. in the AC ESS FEED P/b comes on Amber accompanied by ECAM activation when AC ESS BUS is not electrically supplied.

Q34. Which buses are powered if GEN 1 fails when DC TIE p/b is OFF?

A34. The following busses are powered :-

(i) AC BUS 2

(ii) DC BUS 2

(iii) DC BAT BUS

(iv) DC BUS 1



Q35. What is the AUTO function of the GALLEY p/b? Or when is the main galley power automatically shed?

A35. When the GALLEY P/b s/w is in AUTO :-

(a) The Main and the Secondary galley are supplied.

(b) The Main galley is automatically shed when :-

— In Flight : Only one generator is operating

— On Ground : Only one engine generator is operating.

(All galleys are available when the APU GEN or EXT PWR is supplying power)

Q36. What is so special about green colored CBs?

A36. The Green colored S/B’s are the ‘monitored’ C/B’s. When out for more than one minute, the

‘C/B TRIPPED’ warning is triggered on the ECAM.

Q37. ELECT DC BAT BUS FAULT has appeared on ECAM. What are the consequences?


*Crew awareness


ECB is no longer supplied. >>INOP SYS : APU FIRE DET.



*Stick & rudder pedals lock (by AP)

*FWD(AFT) Cargo fire ext.

*FWD Cargo heat controller

*FWD Cargo ISOL. Valves.

*APU Fuel LP Valve

*Manual pressure control

Q38. In a flight, Electrical page has appeared on S/D and you see IDG temp is pulsing. What do you think of this situation? What will be your actions?

A38. The IDG Temp. flashes when :-

147 C < T < 185 C (Advisory)

Reduce IDG load, if possible (GALLEY or GEN OFF). If required, restore when the temperature has dropped.

Restrict generator use to a short time, if the temperature rises again excessively.

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2 thoughts on “ELECTRICAL SYSTEMS”

  1. Hi there, Q11. at below 50knots, it is stated that the STAT INV is ‘activated’, shouldn’t it be ‘deactivated’ instead? correct me if I am wrong, thank you…

    • static inverter activated because BAT 1 is supplying the AC ESS BUS (if AC BUS 1 and 2 are lost).At speeds below 50 knots, RAT is not deployed, thus EMER GEN is not operating.

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