Systems - Electrics Flashcards
On an unpowered airplane, what instruments are powered when the Battery switch is turned on?
- Captain PFD
- Captain ND
- IFSD
- left CDU
- captain radio stack
- PA
How many batteries are on the 777?
2
- Main
- APU
Can the battery switch be turned off:
- in flight?
- on the ground?
- Inflight system logic prevents it from being turned off
- On the ground it will turn off
How long should the Main battery power the STBY system?
At least 10 minutes
You enter a cold dark airplane and find the EXT PWR AVAIL lights on. What must be done before selecting external power ON?
Interior safety inspection
When you arrive at the airplane, primary and secondary external power are both connected and selected on. As part of your preflight duties you start the APU. What bus does it automatically connect to?
Left main bus
What should you check before disconnecting external power?
APU running
When does the APU shut down automatically?
- In unattended mode for any parameter exceedance, no cool down period
- In attended mode for fire, overspeed/loss of overspeed protection/speed droop, APU controller failure, also for high EGT/oil temp or low oil press. No cool down period
When will the APU fire bottle discharge automatically?
In unattended mode fire bottle discharges for fire signal from either detector loop.
What does the APU fault light indicate during and after APU start?
-During a start an APU controller is doing a self test
-After a start an automatic shutdown occurred due to fault or fire
When does the APU start automatically?
Loss of both transfer busses
What is the altitude limit for APU start?
43,100
What is the purpose of the back-up generators?
- To house the PMGs
- To power one or both transfer busses when respective AC power is lost
- To provide redundancy for the AUTOLAND system
What is the STBY bus normally connected to:
- directly?
- abnormally?
- L XFR bus normally
- CA INST bus via inverter abnormally
What is the main purpose of the XFR buses?
To power essential Loads/Equipment
What causes the generator drive light to illuminate?
Low oil pressure
What causes the generator drive to disconnect?
High drive temp
How does the IDG provide constant level of output through the varying engine speed range?
Through a Constant Speed Drive
What is the source of DC power in normal flight?
Through the TRUs whenever the transfer busses are powered by their respective main AC busses.
What is the primary source of standby power during a dual engine failure and APU not working with all normal AC and DC power sources failed?
The RAT via C1 and C2 TRUs to the respective CA and FO instrument busses
What causes the RAT to extend automatically?
-During a dual enginge failure with a loss of Center Hyd press
-Both AC transfer busses unpowered
-All Hyd system pressures low
What system does the RAT prioritize electrical or hydraulic? How?
It prioritizes the hydraulic system by shedding electrical loads during low hyd pressure situations. Electrical power is supplied to the standby system by the main battery during shedding.
Without AC power, what is the source of fuel for an APU start? And with AC power?
With no AC power established a dedicated DC pump in left main tank. With AC power established left main tank forward AC pump
What batteries are required to start the APU?
Both main and APU battery
When does the backup AC system test?
After engine start
During a walkaround, an APU fire is indicated by an intermittent horn and red light on the aft panel of the nose wheel strut. What’s your action?
Back up the automatic system by shutting down the APU and discharging bottles.
Without external power, what will the APU power upon startup?
The entire electrical system.
With primary external power on-line and powering the left and right AC buses, what will happen when the APU is started?
APU will power the left main AC bus
What does the external power AVAIL light indicate?
Voltage and Frequency within limits
With no other power source, what is powered when the PRIMARY EXT PWR switch is pushed?
The entire electrical system
Which external power should be connected first?
Why?
Primary
because it powers the ground handling bus
What is on the ground handling bus?
- Cargo doors handling and lights
- Potable water servicing
- Maintenance access lights
What is on the ground service bus?
- APU and Main battery chargers
- left FWD main fuel pump
- galleys/outlets
What happens if in addition to Primary EXT you press the SECONDARY EXT PWR switch to ON?
The electrical system is split in half
How do ramp personnel know if the External power is in use by the cockpit crew?
Exterior panel NOT IN USE light not illuminated
How would you disconnect (or reset) the IDG from its main AC bus?
Gen control switch off then on
If you push the an IDG drive switch, can it be reset?
No, MX only function on the ground
An EICAS message and ELEC synoptic show the loss of both AC transfer buses. What automatic action will occur?
APU will start and RAT will deploy
How many backup generators can be used at the same time?
One at a time, because there is only one converter for both generators
How does the electrical system split the Autopilots during an Autoland operation?
The right autopilot electrical power is transferred from the right main AC bus to the right back up generator which powers the right transfer bus which powers the right autopilot
What powers the flight control buses if the backup generator PMGs fail?
Main DC buses, CA flight instrument bus, Hot batt bus, 1-minute batts during power transfer
What is the function of ELMS?
For load shedding logic
What equipment might be shed?
Galleys, outlets, recirc fans, various pumps
When would load shed normally occur?
With one source of electrical power and high electrical load demand
Where can verification of load shed condition be found?
ELEC synoptic page
If the RAT was deployed, what does it power?
C1 and C2 TRUs
What uses DC power on the 777?
- PFD
- ND
- GPS
- ADIRU
What is PSA and what is each PSA powered by:
- normally?
- backup?
PSAs are Power Supply Assemblies for the flight controls and are:
* normally powered by PMGs
* backed up by Main DC buses or Batt Hot bus
