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. What would you like to do?
What is the generator cut-in range
- 320-480 cycles per second
What range does the airframe mounted gearbox shift
Does the OFF position stop the generator?
No, it disconnects it from its bus
What three situations will the generator caution light illuminate
- generator malfunction
- bus fault
- switched to OFF
When a generator drops off line due to a bus fault, can you get a good crossover?
No, If the malfunction is a bus fault, the protection panel will not allow a generator reset or bus transfer to the opposite generator
What does the static inverter power?
- either engine start (ground or air)
- right engine AC sensors
- both fuel quantity sensors and oxygen quantity
How is the static inverter activated?
- pushing either engine start button
- advancing either throttle to AB
- holding the fuel/oxygen check switch
How are the engine Tachometers powered?
they have their own independent generator in the engine accessory gearbox
Name the AC powered engine sensors
- oil pressure
- fuel flow (also needs left essential DC)
- hydraulic pressure
- fuel quantity
- oxygen quantity
How and which busses does the APU power?
The APU connects to the AC busses which power the TRUs which power the DC busses
Indications of generator fail with good crossover
illumination of MASTER CAUTION and generator lights and caution alert messages
How many times can a generator be reset?
Right gen fail no cross indications
- MASTER CAUTION, RIGHT GENERATOR, RIGHT FUEL PRESS, ANTI-ICE illuminate
- HUD and UFCP go blank
- MFD reverts to backup display
- right oil pressure and fuel flow, oxygen quantity and all three fuel quantity show OFF
- Flight control hydraulic indicator freezes at last position
Left gen fail no cross indications
- MASTER CAUTION, LEFT GENERATOR, LEFT FUEL PRESS illuminate
- Illumination of the AOA indicator lights and CAUTION alert message on the HUD and MFD
- left oil pressure and fuel flow indicators show OFF
- utility hydraulic pressure gauge freezes
Airframe mounted gearbox failure indications
MASTER CAUTION, generator and hydraulic lights
Gearbox failure to shift indications
- occurs when moving throttle(s) through 65-75% RPM
- Indications are the same for a generator failure
Partial electric failure indications
same as gen fail with crossover
Partial electric failure indications with no cross
- Flaps and boost pump operates slower or not at all
- Slow or inop boost pump may lead to Fuel low pressure light
- HUD operation/display may be affected
- TRUs may drop offline
How is the Caution Light Panel and MASTER CAUTION light powered
- both are DC in bright and right AC in DIM
- FIRE light is bright and DC only
How can you light the WCA lights without DC power
Set to DIM
How can you light the WCA lights without AC power
Set to BRIGHT
Does a GENERATOR light always mean a generator failure?
HYDRAULIC light illuminate when hydraulic pressure drops below ___ or what?
When does the FUEL PRESSURE light illuminate?
fuel pressure drops below 6psi (normally 10)
When does the ENG ANTI-ICE ON light illuminate?
switched on, right fail gen no cross
When is the ANTI-ICE system on w/o the light?
below 65% RPM
When does the OXYGEN light illuminate?
below 1 liter, may blink due to sloshing
When does the FUEL LOW light illuminate?
7.5 seconds at 250lbs
Will the MASTER CAUTION light reilluminate after being reset when the second tank goes below 250?
What is the approximate life of the battery after TRU failure?
During normal operation, what is the primary DC power source
Which of the following aircraft components are inoperative when there is complete DC electrical failure
- AB operation
- Crossfeed operation
- Landing Gear Indicators (Bright mode)
- Fire warning lights
The right TRU receives power from the ___ and the left receives power from the ___
- right AC bus contactor
- left AC bus contactor
Can one TRU carry the entire DC load
What if both TRUs fail?
the battery picks up the DC load for only the two essential DC busses
When is the non essential DC bus shed?
when the bus drops from 28 VDC to 24 VDC
What may cause a momentary illumination of XMFR RECT OUT?
- flaps moving
- fuel/oxygen quantity check
- AB ignition
Is the battery charging when the APU is connected?
What three times is battery power required?
- non-APU start
- both TRUs fail
- both gen inop
Indications of a single TRU fail
AVIONICS alert on the HUD/MFD
Indications of both TRU fail
MASTER CAUTION, XMFR RECT OUT illuminates and caution alert is displayed on MFD
If ON, when does the battery drop off line?
drops below 10V
If ON, indications of weak battery
- low volumes
- raspy interphone and poor radio transmission capability
- caution panel lights dim
If the battery is on, power can be conserved by turning off what
- UHF backup control
- emergency flood lights
Total DC failure recovery considerations
chase ship or to a VFR field (Lost all comm/navigation capability)
Right essential DC bus failure recovery considerations
- standyby instruments for control and performance
- stay VMC
- use chase ship to lead back
- Squawk emer and use NAV B/U for the VOR
- Alternate gear extension
Left essential DS bus failure recovery considerations
- stay VMC or use chase to lead back
- No-flap required
Total electrical failure recovery considerations
- standy by instruments only
- Idle to Mil only, no AB.
- No airstart
- alternate gear extension with no indication
- No flaps trim or speedbrake
Right AC bus Failure considerations
- MDP and HUD inop.
- Only backups on MFD.
- Must use UHF/NAV backup control panel.
- No flaps, trim, right boost pump, A/C and eventually canopy seal
Left AC bus failure considerations
- mostly a concern at night since normal aircraft lighting is affected.
- SAS, rudder trim and left boost pump are inop
What is AC power provided and how are they powered?
2 independent generators powered through airframe mounted gearbox
TRUs convert power from AC to DC or DC to AC?
AC to DC
TRUs convert ___ - ___ volt three-phase AC power to __ ___ DC power
What is the purpose of the TRUs?
Provide primary DC power source
What is the alternate DC power source?
24-volt lead acid battery
What two things does the battery provide power to when the TRUs are offline?
Essential DC busses and battery bus
What position should the battery switch be in for an APU start?
What is the primary purpose of the battery?
What is the static inverter powered by?
What does the static inverter do?
Converts DC to AC for instruments monitoring right engine start
What three ways is electrical power distributed in the T-38?
- Left and right AC busses
- 3 DC busses (1 non-essential)
- and battery bus
EGI storage and memory requires at least ___ secs of aircraft power after turning off the EGI switch on the AAP
AC Electrical Components
- (GAP SAAB)
- AC Bus
- Protection Panels
- Static Inverter
- AC-powered instruments
- Bus contactors/transfer relays
What are the three main specifications of the generators?
- three phase
- 320-480 cycle
- 115-200 volt
What does the engine-mounted gearbox power besides the generator?
What RPM does gearbox shift occur?
Each generator supplies AC electrical power to what?
AC electrical bus
Generators normally carry ___ the electrical load
If one generator fails, the other will supply AC power to both systems dependent on what?
What are the three generator switch positions?
On, Off, and Reset
What does putting the gen switch to OFF do?
Disconnects the generator from the circuit. DOES NOT turn off the generator (engine windmilling)
How would you attempt to get a failed generator back online?
Select RESET then ON
When do GEN caution lights illuminate?
GEN switch in off or any GEN malfunction or bus fault
How many bus contactors are there for each generator and where are they?
2 located in the aft electrical compartment (behind the rear seat)
What is contained within the bus contactors?
Main relays and transfer relays
What is the function of the main relays within the bus contractor?
Connects generators to their respective busses
What is the function of the transfer relays within the bus contractor?
Connect bus loads to opposite generator in case of a malfunction.
What does the transfer relay do in the event of a bus fault?
Does not allow a transfer to the other generator
What are the 2 times a generator will disconnect from its bus?
Gen malfunction (cross) and bus fault (no cross)
What are the 2 times in the checklist that the transfer relay (crossover) is checked?
R-L checked on R engine start. R-L and L-R checked during before taxi check
What are the 3 ways to activate the static inverter?
- Placing either throttle in AB
- using fuel/o2 test switch
- pressing start button
Static inverter provides power to the following equipment
- Right engine AC instruments
- Ignition - L and R
- Fuel and O2 quantity gauges
What do most standard AC instruments do when they fail?
They freeze (AC lies, DC dies)
What would happen to your instruments with a loss of AC?
Loss of EED indications (oil, fuel flow, fuel quantity) hydraulic and O2 freeze
What type of power does the APU provide?
AC (replicating generators and engines running)
What happens when a generator connects to a bus after an APU is connected?
External power relay disconnects the APU
What must you sometimes do to get the aircraft to accept APU power?
Cycle battery off, then on
What type and amount of power do the TRUs put out?
What happens if one TRU fails?
The other will carry the entire DC electrical load
How many and what types of DC busses are there?
3 - 2 essential, 1 non-essential
What DC busses are powered if the battery is the only source of power?
2 essential busses
What are the 4 situations when the battery would be the only source of DC power?
- Starts without an APU
- both TRUs failed
- Both GENs inop
- DC components causing a drain on DC bus below 24 volts
What three things are on the battery bus?
- static inverter
- L/R start control
- L/R afterburner ignition control
What is the min volts for the battery to connect to the DC bus?
What is the min voltage for the battery to stay online?
How long (approximately) will battery power last?
15 mins at 80% charge
What are the DC-powered instruments and displays?
- Flap position indicator
- EED (EGT. Nozzle position)
- standby attitude indicator
Are map lights DC or AC?
Is interior lighting DC or AC?
During an AC power failure, what will happen to the interior lights?
They will revert to DC - bright during night, dim during day
Is bright mode for the WCA system AC or DC?
What are the 4 instruments not affected by the caution/light panel dimmer switch?
- Marker beacon
- FIRE lights
- takeoff trim indicator lights
How do you dim the WCA lights?
Ensure rheostat is out of off, place switch in DIM to change from DC to AC
What happens of an AC power failure occurs for the WCA lights?
Revert to DC (bright) mode
What 2 lights cannot be dimmed?
FIRE lights and Takeoff trim indicator
What 3 lights are inop with a DC failure?
- FIRE lights
- Master Caution Lights
- RCP nosegear light
What 2 things have to happen for the tone test pattern to work?
MDP timed-in and gear warning silence button depressed
What 3 things does the test switch on the right front console test?
- tone test pattern
- fire detection system
- and master caution and caution panel lights
What are the 2 places the rotating beacon is located?
Bottom of fuselage and vertical stab
What 3 places are position lights located?
wintips, vertical stab, lower fuselage
What are the two main features of the landing/taxi light?
Retractable, and dual filament
What two things must be activated for the landing/taxi light to be extended?
Position lights ON, and landing gear handle DOWN
When are both filaments in the landing light on?
When the aircraft is airborne and the gear is down
When is only one filament in the lighting light on?
When the weight of the aircraft is on the main gear
How long does it take the landing light to retract?
What would you like to do?
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