What are the two “basic principles of operation” for the 737 Electrical System?
- no paralleling of AC sources of power
- a new connecting source disconnects an existing source
(Sec 6.010 p 1)
What are all the sources of AC power?
- two Engine-Driven Generators
- one APU Generator
- external power
(Sec 6.010 p 1)
What could cause the illumination of the Generator DRIVE light?
Low oil pressure caused by:
- IDG failure
- engine shutdown
- IDG disconnected by activation of the DISCONNECT switch
- IDG auto-decouple due to high oil temp (182 deg C)
(Sec 6.010 p 5)
What happens when positioning the GRD PWR switch ON?
external electrical power is connected to both Transfer Busses
(Sec 6.010 p 7)
What does the BUS TRANSFER switch, in the AUTO (guarded) position, allow?
allows the Bus Tie Breakers (BTB) to automatically maintain power to AC Transfer Busses from any operating generator or external power
Which light(s) indicate(s) the APU is ready-to-load, but not powering a bus?
APU GEN OFF BUS light (>95% RPM)
Sec 6.010 p 12
If the AC Transfer Buses are powered by External Power, momentarily positioning either APU GEN switch ON will cause the APU to power which bus(es)? What lights would you see?
- connects APU power to both Transfer Busses
- disconnects external power, if connected
- the opposite side SOURCE OFF (amber) light illuminates until the other APU GEN switch is moved to ON
(Sec 6.010 p 13)
When the APU is powering a Transfer Bus, how can you power the opposite Transfer Bus?
APU will power both transfer busses when APU is selected to replace ground power
If APU is powering one transfer bus and the other bus is powered by IDG, momentarily move the respective APU GEN switch to ON or the respective GEN switch to OFF
(Sec 6.010 p 13)
What buses are shed when the APU is operating in flight as the single electrical source?
all Galley Busses and Main Busses are automatically shed, IFE Busses are shed if load exceeds design load limits
(Sec 6.010 p 13)
Moving GEN (Generator) switch to ON powers which bus? What lights would you see?
Transfer Busses. When GEN is connected, the respective GEN OFF BUS (blue) light extinguishes
(Sec 6.010 p 14)
Describe the Automatic Generator Online feature.
In the event the aircraft takesoff with APU powering both Transfer Busses, if the APU is shut down or fails, the engine generators are automatically connected to their related Transfer Busses
(Sec 6.010 p 15)
What does the ELEC light (amber) indicate?
Indicates a fault in the DC Power System or Standby Power System
(Sec 6.010 p 17)
When does the Cross Bus Tie Relay open and isolate DC Bus 1 from DC Bus 2?
- GS capture during a F/D or A/P ILS approach
- Bus Transfer Switch positioned to OFF
(Sec 6.010 p 18)
Which Bus is always connected to the battery?
Hot Battery Bus
Sec 6.010 p 21
When does the BAT DISCHARGE light (amber) illuminate?
Excessive battery discharge is detected in the Main Battery and/or Auxiliary Battery
(Sec 6.010 p 22)
What is/are the alternate power source(s) for AC standby power?
AC Standby Bus is powered from the batteries via the Static Inverter
(Sec 6.010 p 25)
How long will two fully-charged batteries provide standby power?
Minimum of 60 minutes
Sec 6.010 p 24
With the loss of all engine or APU electrical power, the battery will be powering which buses if the STANDBY POWER switch is in AUTO? Is this the same in flight and on the ground?
- AC Standby Bus powered from batteries via Static Inverter
- DC Standby Bus, Battery Bus, Hot Battery Bus, and Switched Hot Battery Bus are powered directly from the batteries
Unlike older 737 variants, this is the same both in the air and on the ground
(Sec 6.010 p 25)
