SIT question bank (oral prep) Flashcards
(476 cards)
What does the “AVAIL” light mean on the external and APU PWR switches?
Power quality is acceptable
What bus is powered on the ground when APU GEN 1 or EXT PWR 1 is available?
Ground handling bus
When is the main deck cargo handling bus powered?
Whenever EXT 2 or APU 2 is plugged in and AVAIL (but not selected ON).
What electrical power source would you need to select if cargo handling is required?
EXT 1 or APU 1
When is the ground service bus powered?
Anytime AC bus 1 is powered.
Or, if AC bus 1 not powered, can be powered from APU 1 or EXT 1 by pressing the Ground Service switch (1L).
What is the function of the standby power switch in AUTO?
It allows the standby busses to be powered by available sources automatically. (Referring to main standby bus and APU standby bus).
Where would you find the electrical power up procedure?
FCOM Vol. 1
What does a bus isolation (ISLN) light illuminated indicate?
It means that the BTB is open and the AC bus is isolated from the synchronous bus. (bus still powered, just isolated.)
What happens when you press a generator drive disconnect switch? (DRIVE DISC)
Disconnects IDG from engine. Opens related GCB.
What condition would automatically disconnect the IDG if not manually disconnected?
High IDG oil temperature
How do you reconnect an IDG that has been disconnected?
You don’t. MX has to do it on the ground.
What does a generator DRIVE light indicate?
-High IDG oil temp
-Low IDG oil pressure
-Uncorrectable generator freq. fault
What are some of the equipment items powered on the utility busses?
-Forward main fuel pumps 2 and 3
-Forward overr/jett pumps 2 and 3
-Center overr/jett pump CWT L
-Galley equipment
Describe the electrical load shedding process.
ELCUs automatically control load shedding and shed utility busses as needed. Whatever order the ELCU removed items, it will restore them in reverse order.
What is the purpose of the electrical system overload protection?
So the main AC busses do not get overloaded. You have systems in place to prevent the loss of critical components due to an overload. The less important things are shedded to preserve the more important things.
During load shedding, would you expect to see an EICAS advisory message ELEC UTIL BUS L, R?
No
What are the main AC electrical power sources?
-2 APU gens
-2 EXT power
-4 IDGs
Describe the function of the split system breaker (SSB).
It divides the synchronous bus into 2 parts. It allows for segregation of non-synchronized power sources to power their own sides of the system, and also allows a single source or multiple synchronized sources to power the entire system.
Describe the electrical system sequence of events during an engine start with the SSB open.
APU GEN 1 and 2 are being used, SSB open. After 1 engine start, that side is all off IDG, SSB still open. After an engine started across the SSB, the SSB closes.
Describe the electrical system sequence of events with a single power source with the SSB closed during an engine start.
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Which bus powers the captain transfer bus and main standby bus?
AC bus 3
Which bus powers the First Officer transfer bus?
AC bus 2
Which bus provides power for both transfer busses?
AC bus 1
What are some items on the ground service bus?
-Battery chargers
-Fuel pumps for APU start
-Flight deck flood lights/service lights
-Nav lights
-Misc. outlets