Primary ac power comes from the
dc power comes from
two transformer-rectifiers (TRs), three dc outputs from each permanent magnet generators (PMGs), the battery, and the battery charger
The electrical RESET button...
This button provides master reset capability for any failed generator or electrical system relay without interrupting operational circuits
PMG power goes to
- L: FCC A (CH 1 & 2), Essential bus backup
- R: FCC B (Ch 3 & 4), Essential bus backup
Main Essential bus power comes from
Electrical fault protection logic: Generator fault
1. If a generator fault occurs, generator isolation circuitry removes the affected generator from its buses
2. All generator faults except N2 underspeed require manual generator reset
3. Generator reset is successful only if the out‐of‐tolerance or fault condition has cleared
4. If the generator fault remains, bus tie circuitry allows the remaining generator to power all electrical buses
*During an N2 underspeed condition, the affected generator is automatically restored when rpm returns to normal range.
Electrical fault protection logic: Short or overload condition
1. The right generator attempts to power through the short and if unsuccessful, trips offline
2. The left generator is then connected to the right buses by the bus tie circuitry, attempts to power through the short, and,if unsuccessful, also trips offline
3. Approximately 1 second after the dual generator outage, the generator automatic reset logic resets both generators.
4. If the bus or equipment fault has cleared, both generators remain online to power their respective buses
5. If the bus or equipment fault remains, the right generator trips offline again, but bus isolation circuitry now prevents the left generator from picking up the right buses (GEN TIE caution light).
6. The left generator remains online to power the left buses and the R 28 vdc bus. The R 115 vac bus, R 26 vac bus, and battery charger are unpowered, and the battery runs the maintenance bus.
*This entire process may take as long as 16 seconds.
For the ac bus isolation and generator automatic reset circuits to operate, ...
the GEN TIE switch must be in NORM, the BATT switch must be ON, and the PARK BRK handle must not be set
During initial engine start (battery or external power) GEN TIE circuitry requires ... to properly function.
a set PARK BRK handle
If the left and right buses are isolated because of a detected fault (e.g.,RGEN caution and GEN TIE caution light), cycling the GEN TIE switch ...
reenergizes the faulty bus/equipment and may cause further damage or loss of the remaining generator.
There (is/is not) a cockpit warning of a single TR failure
There is not a cockpit warning of a single TR failure (no caution and no MSP code). TR operation is checked on maintenance phase inspections.
Regardless of ... switch position, the PMGs come online when the engine reaches approximately ... N2 rpm on spool up and remain on until ... N2 rpm on spool down.
Regardless of generator control switch position, the PMGs come online when the engine reaches approximately 50% N2 rpm on spool up and remain on until 20% N2 rpm on spool down.
What powers the maintenance bus
What does the maintenance bus operate
the canopy, ladder, and maintenance monitor in the absence of ac electrical power.
In the unlikely event of a total ac/dc failure inflight,...
the battery provides the last level of essential bus backup capability, providing about 5 to 10 minutes of power for the FCCs, after which aircraft control is lost.
Regardless of BATT switch position, the battery charger supplies charging power to the battery anytime the ... bus is energized.
right 115 vac
FCC electrical redundancy
1. Primary power: respective PMG output
2. If a PMG output should fail, that FCC channel is powered by the essential bus, which also has several sources of redundancy (the TRs, the PMGs, and the battery).
*The BATT switch must be ON for either a PMG or the battery to power the essential bus.
3. Additionally, “keep alive” circuits connected directly to the maintenance bus provide each FCC channel with an uninterrupted backup power source during normal bus power transients.
On the ground with the BATT switch ON,the ... circuit disconnects the battery from the essential bus and returns the BATT switch to OFF ... after ac power is removed from the aircraft.
On the ground with the BATT switch ON,the automatic battery cutoff circuit disconnects the battery from the essential bus and returns the BATT switch to OFF 2 minutes after ac poweris removed from the aircraft.
The automatic battery cutoff circuit is disabled when ...
the APU comes online
Nominal voltage for a “good” battery should be ...
23 to 24 vdc.
Minimum battery voltage is ... . EFD blanking and/or uncommanded APU shutdown should be anticipated with battery voltage ...
Minimum battery voltage is that which provides a successful engine start (e.g., APU remains online and the EFD remains powered to provide indications of RPM and TEMP). EFD blanking and/or uncommanded APU shutdown should be anticipated with battery voltage at or below 18 vdc
If the battery gauge fails to jump to approximately ... with one GEN online, ...
If the battery gauge fails to jump to approximately 28 vdc with one GEN online, a battery charger malfunction has occurred which requires maintenance action prior to flight.
If a dual GEN failure occurs, the battery gauge is reconnected to the essential bus and must be referenced to determine the essential bus power source.
*If the battery gauge remains at approximately 28 vdc, an EBB PMG is powering the essential bus, and FCC operating time is not limited.
*if the battery gauge indicates 24 vdc or below, the battery is powering the essential bus, and FCC operating time is limited to about 5 to 10 minutes.
*The FCCs should continue to operate down to a battery gauge voltage of approximately 18 vdc.
The aircraft buses are energized by external power in the same manner as if a generator were operating provided ...
the BATT switch is OFF or the parking brake is set.
The first ground power switch placed to ON must be held for ... to complete an avionics overheat BIT
Circuit breakers in the cockpit
- 1. LAUNCH BAR
- 2. FCS CH 1
- 3. FCS CH 2
- 4. FCS CH 3
- 5. FCS CH 4
- 6. HOOK
- 7. LG