737 Quiz: Boeing Flight Deck Electrical Systems

Study Notes

Electrical System Overview

Transfer bus 2 prioritizes the shedding of galleys and main bus during overload situations.
If overload persists, transfer bus 1's galleys and main bus are shed next.
In case of continued overload, in-flight entertainment (IFE) buses are the last to be shed.
Automatic load restoration occurs when there is increased generator capacity; manual restoration is possible using the CAB/UTIL Power Switch.

APU Load Shedding

When the APU is the sole power source in flight, all galley and main buses are automatically shed.
If overload continues, both IFE buses are also shed.
On the ground, the APU can support a full electrical load but will shed galley and main buses to manage overload.
Manual restoration of power can be performed similarly by toggling the CAB/UTIL Power Switch.

Power Source Management

The APU GEN switch connects APU power to both transfer buses; the last selected source powers both.
It is not possible to independently power transfer buses with different sources (APU and external).
Engine generators can power transfer buses by temporarily switching the generator switch ON.

Transfer Bus Operations

When external power or APU is supplying, and engine generators are applied, the system maintains power continuity.
In flight, engine generators usually power their respective transfer buses, and backups are facilitated automatically through bus tie breakers (BTBs).
If an engine generator fails, the other engine generator can supply power to both transfer buses.

System Redundancy Features

The APU can power either or both transfer buses and is equipped with an automatic generator on-line feature.
Upon APU shutdown or failure, engine generators automatically connect to their respective transfer buses, activating this process only once during flight.

Bus Tie System

Either generator or the APU can power both transfer buses; an automatic transfer system activates if any source disconnects.
The BUS TRANS switch in AUTO ensures power redirection to the unpowered transfer bus via BTBs.

Flight Deck Auxiliary Power System

Comprises power converters and AC outlets for Flight Deck personal electronic devices (PEDs).
Protective devices prevent tampering with the outlets; correct insertion of plugs is required for power activation.

Automatic Load Shedding

Single generator operations shed electrical loads incrementally by sensing actual load levels.
A specific list identifies essential equipment functional on battery power when all generators are inoperative.

Description

Test your knowledge on the electrical system of the Boeing 737 flight deck, including the operation of the Bus Trans switch and the Auxiliary Power System. Explore how the transfer buses are powered and controlled in different scenarios.