Electrical

Question 1

Q.2.1. During cruise, you notice a BAT DISCHARGE light illuminated. When you check the battery voltage, what would you expect to see as normal?

Answer 1

22-30 volts.

Reference: B737 NG/MAX 6.2.5.2

Question 2

Q.2.2. How long can a fully charged battery/batteries provide standby power?

Answer 2

Single Battery: 30 minutes minimum
Dual Battery: 60 minutes minimum

Reference: FRM B737NG/MAX 6.2.5.2

Question 3

Q.2.3. You receive a MASTER CAUTION/ELEC and notice a DRIVE light illuminated on the overhead panel. What has occurred and what should be your next course of action?

Answer 3

Integrated drive generator (IDG) low oil pressure caused by one of the following:
IDG failure
Engine shutdown
IDG automatic disconnect due to high oil temperature
IDG disconnected through generator drive DISCONNECT switch
Carefully assess any related information. Reference the QRH for corrective action.

Reference: FRM B737NG/MAX 6.1.3

Question 4

Q.2.4. Why does the QRH direct the generator drive DISCONNECT switch to be placed in the Disconnect position?

Answer 4

Disconnection reduces risk by preventing further generator drive damage.

Reference: QRH 6.1

Question 5

Q.2.5. What does a SOURCE OFF light indicate?

Answer 5

No source has been manually selected to power the related transfer bus, or the manually selected source has been disconnected.

Reference: FRM B737NG/MAX 6.1.4

Question 6

Q.2.6. How is the transfer bus powered if the respective IDG is disconnected?

Answer 6

If the BUS TRANSFER switch is in the AUTO position, the source powering the opposite transfer bus automatically picks up the unpowered transfer bus through the bus tie breaker.

Reference: FRM B737NG/MAX 6.2.3

Question 7

Q.2.7. While in cruise flight, you receive a MASTER CAUTION/ELEC and notice a TR UNIT light illuminated on the overhead panel. What could have caused it?

Answer 7

TR1 failed; or
TR2 and TR3 failed

Reference: FRM B737NG/MAX 6.1.2

Question 8

Q.2.8. While in cruise flight, you receive a MASTER CAUTION/ELEC and the following lights on the overhead panel: TRANSFER BUS OFF (both), SOURCE OFF (both), and GEN OFF BUS (both). What provides power to essential systems immediately?

Answer 8

Standby power system:
The AC standby bus is powered from the batteries via the static inverter.
The DC standby bus, battery bus, hot battery bus, and switched hot battery bus are powered directly from the battery/batteries.

Reference: B737NG/MAX 6.2.6.2

Question 9

Q.2.9. What does the STANDBY PWR OFF light indicate?

Answer 9

Illuminated (amber) – One or more of the following buses are unpowered:
AC standby bus
DC standby bus
Battery bus

Reference: FRM B737NG/MAX 6.1.3

Question 10

Q.2.10. With a LOSS OF BOTH ENGINE DRIVEN GENERATORS, what other source of electrical power may be available?

Answer 10

As the only power source, the APU generator can meet electrical power requirements for all ground conditions and most flight conditions.

Reference: FRM B737NG/MAX 6.2.2.2

Question 11

Q.2.11. What considerations should you consider for starting the APU in flight following a LOSS OF BOTH ENGINE DRIVEN GENERATORS?

Answer 11

APU start attempts are not recommended above 25,000 feet
• With both busses off, only one start attempt is recommended. Multiple start attempts reduce standby power capacity

Reference: B737NG QRH 6.5/B737MAX QRG 6.6

Question 12

Q.2.12. If the APU generator is the only remaining source of AC power, can you continue to your destination?

Answer 12

Only if the destination airport is the nearest suitable airport to you, as directed by the AOM and QRH.

Reference: AOM 5.1.1.2/B737 QRH 6.4(MAX), 6.5 (NG)