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Describe the main batteries
24V DC 44 Amp-Hr Nicads
Where are the main batteries located?
On the Left, below the cockpit, forward of the main cabin door.
How are the main batteries cooled?
Via a vent on the front of the battery compartment door, and air exits on the back side of the door.
What do the GCU's (Generator Control Units) do?
Provides electrical system ptotection from the generators in case of an overcurrent by segregating the affected generator from the system and deenergizing and disconnecting it from the Bus if necessary.
What is the Maximun Batt. Temp. limitation?
70 degrees C, and if exceeded, a Master Warning and EICAS message will be generated - BATT 1(2) OVTEMP
What is the minimum voltage required to start the APU?
Where is the backup battery located?
Forward electronic compartment, via the nose wheel well, right side of the aircraft.
Where do you normally want to leave the Backup Battery Swith on the overhead panel?
What is the purpose of the backup battery?
Provides a safe source of power for the GCU to allow the protective function to operate, even in case of a short.
How is the backup battery warmed?
There is a heater connected to battery in the forward electronic component acces panel.
Describe the backup battery.
24V DC 5 Amp lead acid
What does the backup battery power?
GCU's via the Backup Hot Bus
If you are down to Essential Power, how long will aircraft have power?
Approx. 30 min. (Do NOT attempt an APU start) You may drain in the batteries in an unsuccessful attempt at starting the APU.
What will you have on Essential Power?
- RMU 1 and 2
- EICAS screen
- Stdby Airspeed, Att., Alt., Mag.Compass
- Nav 1, Comm 1
What happens if the engines are running and you push the Essential Power switch?
- Generators power the DC Busses
- Batteries power the Essential Busses, hence draining the batteries
- EICAS Caution "ELEC EMERG ABNORM"
If down to Essential Power, how will you stop the aircraft?
Normal brakes with antiskid only down to 10 kts, then Emergency Brake.
If the Battery switch is off and the Essential Bus switch is pressed, will the Essential Busses be powered?
YES (overrides battery switch)
What are the only Busses that are NOT powerded when the batteries are the sole source of power?
Shed Bus 1(2), Ground Service Bus
What systems are AC powered?
Where does AC power originate?
From DC Bus 1, via an inverter
How can the APU be powered for start?
- Battery #2
- Battery #2 with generator assist
Can you start the APU with Batt. #1?
No. Batt. 1 is isolated from the rest of the electrical system anytime an engine or the APU is started.
Will the APU normally power the Shed Buses?
No. To power the Shed Busses move the the Shed Bus switch to "Override" on the ground.
If you are flying and #2 Engine quits and the APU is off, will you be able to power the Shed Busses?
No. Unless you start the APU. The Shed Bus Override operates only on the ground and in flight with 3 or more Generators.
What Battery powers the APU?
The Batteries don't power the APU, they only provide power for starting. In that case #2, minimum of -20 degress C & 23.5 Volts
If the APU is running and the 4 engine generators are also running, what will the APU generator do?
Operate in parallel with generators #2 and #4.
What happens if Gen # 1 fails and the APU is not running?
- BTC 1 closes, and the remaining 3 generators operate as one system.
- EICAS message "Gen. 1 Off Bus"
What happens if you lose Gen. #1 and APU is powered?
- - GLC #1 Opens
- - BTC #1 Closes - Both Batt. powered via #1 side.
- - BTC #2 Opens
- - EICAS message "Gen. #1 Off Bus"
What happens if you have all engine generators fail and the APU is not running?
- Airplane enters Essential Power mode.
- - BTC #1 Opens
- - BC #1 Opens
- - BC #2 Closes to power Central Bus for APU start.
- - EBC #1 and #2 switch ti the alternate position, allowing the Essential Buses to be powered via the HOT Busses.
- - BBR #1 and #2 opoen, EIC closes
Describe what happens with the Electrical System when the APU is started.
- - BC #1 is going to open to isolate transients from Batt. #1.
- - ASC closes (allowing power from Batt.#2 to power the starter generator).
- - 0% in-flight or 3% on the ground, ignition and main fuel.
- - ASC will open at 70% operating speed, ignition off.
- - After the APU reaches 95% operating speed and seven seconds, the maximum fuel selenoid is energized, the ALC will close and connect to the Central DC Bus.
- - BC #2 closes
If the APU is the only generator bus powered in flight, will the Shed Busses be powered?
No. APU Override is a GROUND, Generator switch only.
How many engine driven generators?
4. 1 and 3 from engine #1 and 2 and 4 from engine #2.
What is the maximum amps. for the generator?
What happens if the generator goes above 400 amps?
EICAS display turns yellow; however the generator will not automatically disconnect. Load Shedding is done automatically.
How many volts do the engine driven generators produce?
How are the engine driven generators cooled?
On the bottom of the engine, there is a cooling air inlet and exhaust (uses ram air).
What happens if these vents get blocked by snow as you taxi out?
The generators will overheat and fail.
When will the engine generators come online?
When engine speed reaches 56.4% N2
When will the electrical system operate as two independent systems?
As long as you have 4 or more generators running.
If four engine driven generators are working, what is the position of the BTCs?
BTC #1 is open and BTC #2 is closed
What is one thing to keep in mind if you MEL the APU Generator?
You must have all 4 Engine Driven Generators operating
When will the Shed Busses be powered automatically?
Three Generators running and the switch not in the off position
What is also powered from the Shed Busses for taxi purposes?
Two taxi lights and one landing light in the nose wheel
Where is the ground power plugged into the aircraft?
On the aircraft left side, below the Captain window
What does it mean if you see the GPU Avail light illuminated?
Ground power is plugged in and available for use, check for 27 volts before selecting
What will you see once ground power is powering the aircraft?
A white line on the GPU switch, GPU Avail extinguishes
In what order does each power source takes priority, battery, generator or GPU?
Ground power, generator, battery.
If ground power is powering the system, what happens?
All Busses will be powered but the batteries will not be charging.
What will you have if down to standby power?
Standby instruments, EICAS, RMU's, whisky compass.
What is the minimum volts for ground power?
What should you do before the ground crew pulls ground power?
Diselect the GPU disconnecting it from the system. If you don't you may get a NO DISPATCH message, or worst case the whole electrical system will have an interruption and the airplane will require a reboot. Also there might be an arc from the aircraft to the plug as it is pulled, and the ground person may get shocked.
What does the ground power show on EICAS?
Voltage only, no amps.
Do you need batteries to start the APU?
No. ground power can be used
When will the Ground Service Bus be powered?
When battery switch is off and GPU Avail light is illuminated
What is the Ground Service Bus used for?
- - Cleaning crew - lights in aircraft
- - Passenger cabin lights
- - Lavatory lights
- - Courtesy lights
- - Cockpit dome lights
- - Baggage service lights
What will happen if you lose DC Bus #1?
Lose Captain PFD, Captain MFD and EICAS still function (SG#1 on ESS#1) and lose FO MFD, you will lose AC power, as well as all items connected to DC Bus #1.
What happens if you lose DC Bus #2?
Blanking on Captain MFD, FO PFD and Red X on FO MFD
Will you see a white light on the overhead panel if the generator fails?
No, only if you deselect it. It's also a good idea to pull up electrical page during reset.
What should you check if the flight attendant says the coffee jugs are not working?
- (a) Shed Busses might not be powered
- (b) reset circuit brakers in galley area
What do you want to confirm with the cabin courtesy lighting panel before exiting the aircraft?
Make sure they are in the "off" position (powered by bat #2)
Are there any circuit breaker lights?
No. The labels are illuminated by glow in the dark paint.
What would you like to do?
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