PC-21 Electrical System Flashcards
What is the purpose of the PC-21 Electrical system?
To supply and control 28 VDC to various aircraft systems
How does the electrical system ensure that power is always available to the aircraft equipment under differing operational requirements?
Through a series of busbars as well as manually and automatically controlled contactors.
What are the three sections that is a good way to think about the electrical system?
- Engine compartment
- Cockpit
- Avionics Bay
What electrical components are located in the engine compartment?
1) BATT 1, located on the lower left side of the engine compartment
2) GEN 1 and 2, which are engine driven through the AGB
3) Generator Control Units 1 and 2, which are mounted on the firewall at the rear of the engine.
4) Circuit Breaker (CB) panel on the right-hand side of the engine compartment
What are specs of BATT 1? What are its functions?
- 24 VDC, 25 Ah sealed lead-acid battery
- Supplies power to the BATT BUS and is essential for engine start, supplying power to GEN 1.
What are the specs of the generators?
- 28VDC
- Rated at 300 A
What is GEN 1 employed as?
- Combined starter/generator
- Generates DC Current
What is GEN 2 employed as?
Generator only
What is the function of the GCU?
- Maintain correct voltage from generator
- Protect the electrical system against over/under voltage
- Protect the system against overload
- Protect the system against reverse polarity
- Protect the system against reverse current
Where is the engine compartment CB panel?
Located at the top right hand side of the engine compartment
What is used to control the electrical system in each cockpit?
- ELEC panel on right console in each cockpit.
- 5 switches and push button in front cockpit
What are the switches in the front cockpit ELEC panel?
- BATT 1
- BATT 2
- GEN 1
- GEN 2
- BTC NORM (but tie override switch)
- RESET
Where is the cockpit CB panel located and what is it essential for?
- Right side wall of the front cockpit above the console.
- Contains circuit breakers that are essential for IFR flight.
What are the components in the avionics bay?
- BATT 2
- Emergency Battery
- Avionics Bay CB panel
- Ground Power Unit (GPU) connector, bottom left surface of the fuselage
What are the specs of BATT 2? What does it provide power to?
- 24 VDC, 18 Ah
- Power to BATT BUS and BATT DIRECT BUS
What are specs of Emergency Battery?
- 24 VDC, 2.5 Ah, sealed lead-acid battery
- Supplies to EMERGENCY BUS when all electrical power supplies are lost in flight.
How many distribution bus bars are there?
7
What is basic architecture of PC-21 electrical system?
- Four primary power sources (Generators and Batteries)
- Emergency battery
- Electrical bus bars
What are the 7 buses that are installed in the PC-21?
- BATTERY BUS
- BATT DIRECT BUS
- GEN 1 BUS
- GEN 2 BUS
- EMERGENCY BUS
- NON-ESSENTIAL BUS
- MISSION BUS
Which buses does GEN 1 supply during normal operating conditions?
- GEN 1 BUS
- BATT BUS
Which buses does GEN 2 supply during normal operating conditions?
- GEN 2 BUS
Where does MISSION BUS and EMERGENCY BUS receive power from?
BATT BUS
Where does NON-ESS BUS receive its power from?
GEN 1 BUS
Where does BATT DIRECT BUS receive its power from?
BATT 2
What does the MFD electrical system page show?
A simplified schematic of the system
What voltages and currents are indicated on the schematics?
- Each bus indicates actual voltage
- Each component shows the current in amperes that is drawn from it.
What does a Red warning mean?
- Warning
- Equipment offline and some system function missing
What does an Amber caution mean?
- Equipment offline, but no system function missing
What does Green color scheme mean?
Equipment online, everything normal
What does Grey color scheme mean?
Not powered - if equipment is offline, corresponding connector lines and contactors go grey to indicate they are currently not in use.
What does pilot have control over through GEN 1 and GEN 2 switches?
Line contactors for GEN 1 and GEN 2
What do the BATT 1 and BATT 2 switches control?
Control over BC 1 and BC 2
What powers GEN 1 during engine start?
BATT 1 through starter connector
What occurs if a ground power unit is connected to the aircraft?
Additional box is shown on the MFD ELEC page.
Where are the BATT BUS voltages and sum of the battery currents shown ? What do green, red and amber indicate?
- Lower right hand corner of MFD
- Green indicates within limits
- Amber for a caution
- Red for a warning
What occurs during engine start on internal power?
- Engine start only uses power from BATT 1 only
- BATT 2 supplies power to BATT BUS which is isolated from starting process to ensure BATT BUS voltage is maintained and to protect component from surge
What occurs when 1 generator is shut off or fails?
Remaining generator takes over and supplies the full aircraft electrical load via both generator buses
What occurs if BATT 1 voltage is below 23.6 V?
Battery should be recharged before attempting to start the engine through a GPU.
What occurs if an engine start is attempted with a low BATT 1 voltage? What can be done to avoid this occurrence?
- BATT BUS voltage may drop below the level required to keep the avionics systems online
- Shed all unnecessary loads before attempting an engine start.
What is magnetic latching thinking of the electrical switches?
- Both switches can be OFF
- Only one switch can be ON
What should be ensure during normal operation of the electrical system?
- Areas near flight controls, flaps and airbrake are clear of any personnel before applying electrical power.
- Connecting electrical power may lead to an accidental operation of the hydraulic actuators if an external hydraulic source is connected.
How long will batteries supply essential services for flight and what does this assume?
- Will last for 30 minutes
- Assuming load current to essential service is less than 60A AND batteries are fully charged
How is emergency battery charged during normal operation?
From the BATT BUS
What occurs if all electrical power supplies are lost when airborne?
Emergency battery provides an independent power supply to the EMERGENCY BUS
What components does the EMERGENCY BUS power? For how long will fully charged Emergency battery supply these components?
- Front cockpit SFD
- Air Data Unit (ADU)
- Magnetic Heading Sensor (MHS)
- Inertial separator system in the engine air intake.
- 30 minutes
What does the BTC switch allow the pilot to do?
Allows the pilot to isolate the battery bus from the to generators buses.
What does the red GENS warning on the MFD and DWP mean?
- Possible malfunction of the electrical system and both generators are offline
- Both generators are switched off using the GEN switches on the electrical panel.
What does an amber GEN 1 or GEN 2 caution on MFD/DWP mean?
Either GEN 1 or GEN 2 fails or goes offline
Other generator can still supply electrical power
What does an amber BATTERY caution show?
Either battery is offline or not charged, despite generator power being available.
What occurs if battery 1 has not been charged?
An engine relight may not be possible.
What does an amber EMRG BATTERY caution mean?
1) Emergency battery has failed its built-in test
2) Monitoring system detects a difference of > 3V between the charge from the BATT BUS and the emergency batter
3) The emergency bus contactor is open during normal operation, causing the emergency battery to be out of circuit and the EMERGENCY BUS to be powered from the BATT BUS
Will Emergency battery issues be shown on the MFD ELEC?
No
What does amber GPU DOOR on MFD mean?
GPU Door is open if engine is running and park break released.
What does an amber BATT DISCHARGE status message mean?
If electrical load on either battery is greater than charge applied to it.
What does an amber OVER 60A DISCHARGE status message mean?
Combined discharge from batteries > 60A
