Electrical Flashcards
What causes the IDG drive to automatically disconnect from the engine?
High generator drive temperature
If electrical loads exceed the power available (airplane or external), ELMS automatically sheds the
C2 electric pump
How does the APU generator compare to the IDGs?
It is electrically identical to the IDGs
The entire airplane AC/DC electrical load is supplied by
any two main AC power sources
What does the main DC electrical system use to produce DC power?
TRU’s
The backup generator system automatically powers one or both transfer busses when
approach mode (APP) is selected
The ground handling bus powers the
The forward and aft cargo doors
Secondary external power can power the
Left and right main buses
United SOP concerning connecting external power dictates that primary external power
Is connected prior to secondary external power
Can you turn the battery off in flight?
No, the switch is inhibited
When will the backup generators automatically operate?
When power to one or both main AC buses is lost
Once one engine is started, with no other electrical source providing power and the BUS TIE switches are in AUTO, the _____ powers both main busses
IDG
If an IDG is manually disconnected in flight with the DRIVE DISC switch, can you reconnect it?
No, maintenance action is required on the ground
The _____ powers the AC standby bus if the left transfer bus is not powered.
Standby inverter
What is the maximum altitude for APU start?
43,100 feet
What happens to the APU and RAT when both transfer busses are lost in flight?
The API automatically starts and the RAT automatically deploys
When may the flight crew establish power to an unpowered airplane?
ONLY with maintenance approval
Each engine mounted backup generator contains _____ permanent magnet generator(s) (PMG).
2
The primary power sources for the flight control system are the ____ backup generator PMGs.
Left and right
If demand from the RAT exceeds capacity to provide hydraulic and electrical power, which has priority?
Hydraulic power - electrical load is shed until satisfactory hydraulic pressure can be maintained
If the electrical loads exceed power available (airplane or external), ELMS
Automatically sheds nonessential systems
The main battery provides standby power to the
Hot battery bus, battery bus, and standby inverter.
What are the components of the standby electrical system?
The main battery, standby inverter, RAT generator, and the C1 and C2 TRUs
The main battery charger, when powered, will power the
Hot battery bus
The ground service bus is normally powered by the right main bus. The _____ and _____ are alternate sources of power.
APU generator, primary external power
Which of the following is NOT powered by the ground service bus?
Refueling panel
If primary external power is powering one or both main busses, and then the APU is started, the APU automatically connects to _____ after reaching operating speed.
The left main bus
The _____ normally supply power to the flight control DC electrical system
PMGs
During power source transfers (such as switching from the APU generator to an engine generator) operating sources are momentarily paralleled to prevent power interruption
On the ground
While on the ground, normally the IDG can be electrically disconnected from the main busses by selecting an external electric power source or
by selecting the GEN CTRL switch to OFF
What does the illumination of a generator DRIVE light indicate?
Low IDG oil pressure
The primary external power AVAIL light illuminates when th
Primary power source voltage and frequency are within limits
The external AVAIL light means power is plugged in and
Voltage and frequencies are within limits but no yet selected / connected
When the GEN CTRL switches are ON, the generator breaker is armed to close automatically when generator power is
Available
Inflight, when both BUS TIE switches are set to AUTO, the priority for powering the left and right main busses is the
Respective IDG, APU generator, opposite IDG
Pushing the CABIN/UTILITY power switch to OFF removes power from the
Ground service bus
On the ground, power transfers are made without interruption, except when
Switching between primary and secondary external power sources
When closed, the cockpit door locks automatically if electrical power is available and the Flight Deck Access System switch is powered. If pilots are inadvertently locked out of the cockpit, the only means of entry is to
Use the emergency access code or de power the airplane
The BACKUP GEN OFF Light illuminated indicates
A backup generator failure, a circuit fault or the switch is off
Pushing the IFE/PASS SEATS power switch to OFF removes power from what
All inflight entertainment components
If the Emergency Lights are ARMED, they will automatically illuminate with the
Loss of DC power
The emergency lighting system is powered by remote batteries that are charged by the airplane electrical system. Fully charged, the batteries can provide at least ____ minutes of operation.
15
A white sterile cockpit light is located in the hallway on the ceiling panel above the cockpit door. The light automatically illuminates when altitude is _____ feet MSL and below, and the parking brake is not set.
10,000
Emergency Lights that illuminate the cabin escape path and exits are controlled by the guarded EMER LIGHTS switch on the cockpit overhead panel and the guarded EMERG LIGHTS switch on the flight attendant panel at Door 1L. Which switch has priority?
When pushed ON, the flight attendant switch bypasses the cockpit switch regardless of the cockpit switch position (OFF, ARMED, or ON).
Which EMER LIGHTS switch position(s) will allow the emergency lights battery packs to be charged?
All three positions
The cabin FASTEN SEAT BELTS signs illuminate automatically when the SEAT BELTS selector is set to AUTO and which of the following conditions exist?
Landing gear not up and locked
The IND LTS switch, when held in the TEST position, illuminates all annunciator lights to _____ brightness. After the switch has been held for 10 seconds, the lights _____ .
Full, dim
