Electrical

Question 1

The Boeing B777 is equipped with generators : (type and capacity)

Answer 1

• 2 Engine driven generators - 120 KVA
• 1 APU generator - 120 KVA
• 2 back-up generator - 20 KVA (engine housed)
• 1 RAT - 7,5 KVA
• 2 PMA supplying EEC
• 4 PMA supplying Flight controls

Question 2

What are the conditions for RAT deployment ?

Answer 2

The RAT is deployed :
• automatically if both AC transfer busses lose power in flight.
• manually by pushing the RAM AIR TURBINE switch on the overhead panel.

Question 3

What are the different type of electrical power ?

Answer 3

• main AC power (2 IDGs+ APU generator + PRI/SEC ext. power)
  * backup power (2 variable speed, variable frequency generator + 1 converter)
  * DC power (DC elec. system + main BAT + APU BAT + towing system)
  * standby power (main BAT + standby inverter + RAT generator + C1/C2 TRUs)
  * flight controls power (4 PMGs + 3 flight controls Power Supply Assembly)

Question 4

IFE/PASS SEATS power switch is powering :

Answer 4

• In-Flight Entertainment system
• Passenger seat system
• flight deck entry video surveillance systems
(773 only expect F-GZNH to F-GZNU)
• ground maneuvering camera system
(773 only)

Question 5

CABIN/UTILITY Power switch is powering :

Answer 5

• cabin lighting,
• utility bus,

FCOM 2 / 6-Electrical / 6-20: System Description / AC Electrical System / AC Electrical Distribution / AC MAIN busses

IE : forward galley heater, chiller boost fan, gasper fan, captain’s and first officer’s foot and shoulder heaters, door area heaters, lavatory water heaters and shavers

• galleys.

Question 6

Under which conditions Backup power is automatically selected to provide power to AC Transfer BUSses ?

Answer 6

• only one main AC generator (includes APU) is available, or
• power to one or both of the main AC busses is lost, or
• approach (APP) mode is selected for autoland.

Question 7

When all main AC generators (IDGs + APU) are unavailable, Backup power is providing power to the entire aircraft. To reduce electrical loading on the backup generator, which systems are inoperative :

Answer 7

• TCAS
• SATCOM
• Right HF radio
• Center tank override/jettison pumps : center tank fuel is unusable and cannot be jettisoned.
• Exterior lights (except nose gear landing lights)
• All non-essential cabin equipment (galleys, entertainment systems, etc.)
(773 only)
• Passenger cabin lighting (except night, galley and cross-aisle lights)
(77X only)
Supernumerary cabin lighting (except night, galley and cross-aisle lights)
Cabin temperature control (remains operative, but in degraded mode)

Question 8

In case of a total electrical failure (RAT and APU included), how long can the battery provide electrical power to the Stanby system ?

Answer 8

The main battery can power the standby system for a minimum of 10 minutes.

Question 9

Which equipment is powered by the Ground Handling bus ?

Answer 9

The Ground Handling Bus powers :
• Cargo handling (doors, lights…),
• fueling / defueling operations,
• ground equipments for ground handling.

Question 10

Where is the switch for the Ground Handling Bus ?

Answer 10

The Ground Handling Bus is automatically powered when on ground, there is no manual control.

Question 11

The Ground Handling Bus is powered when…

Answer 11

Ground Handling Bus is automatically powered ON GROUND ONLY when :
• PRI Ext. Power is plugged in, or
• APU is running.
PRI Ext. Power has priority over the APU.

Question 12

When is the Ground Service Bus powered ?

Answer 12

The Ground Service Bus is powered on ground AND in flight when :
• the R MAIN AC BUS is powered via the main AC system,
• the PRI Ext. Power is plugged in AND the “Ground Service” power switch is pushed on the door 2L Attendant Switch Panel (ASP).

Question 13

Which equipment is powered by the Ground Service Bus ?

Answer 13

The ground service bus powers:
• the main battery charger,
• the APU battery charger,
• miscellaneous cabin and system loads.

Question 14

Describe the autoland electrical reconfiguration :

Answer 14

When passing 1500 ft, AUTOLAND reconfiguration activates as follow :
• L IDG -> L Main AC + L Transfer BUS + CAPT. Flight instruments DC BUS
• one of the Backup generator -> R Transfer BUS
•

Question 15

Taking into account the following :
B773-F-GZNU
MEL 24-11-01 : L IDG INOP, maintenance proc. done
NOT TAKEN INTO ACCOUNT BY DSPCH

LFPG-KJFK forecast ETOPS
TRIP 50029...06:00
CONT 3% 1724...00:25
ALTN 3170...00:25
FINAL 2983...00:30

MINI T/OFF FUEL 85906

what is the minimum fuel to go ?

Answer 15

24-11-01 -> dispatch OK ETOPS 180
ground apu +240kg/h
flight APU + 90kg/h

total fuel + 2,5%
mini block fuel = taxi time (h) x 240
+ total endurance (h) x 90
+ total OFP fuel (kg) x 1,025

Question 16

what is the priority for ELMS AC MAIN BUS

Answer 16

FCOM 2 / 6-Electrical / 6-20: System Description / AC Electrical System / AC Electrical Distribution / AC MAIN busses

The source order for powering left and right main busses in flight is the:

respective IDG
APU generator
opposite IDG.

Question 17

what are the condition for an in flight APU autostart :

Answer 17

FCOM 2 / 6-Electrical / 6-20: System Description / AC Electrical System / AC Electrical System Power Sources / APU Generator

APU Automatic Start

In flight, if both AC transfer busses lose power, the APU automatically starts, regardless of APU selector position. The APU can be shut down by positioning the selector to ON, then OFF.

Question 18

where can we find APU consumption ?

Answer 18

QRH / Performances In-Flight / acft. type / Text / Engine Inoperative / APU Operation during Flight