STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS
An external power receptacle and relay
DC indicators and controls
One starter-generator is installed on each engine's accessories drive gearbox. The generators
supply primary 28 Volts Direct Current (VDC) power for the DC power system and also
function as starter motors. Each generator contains a GCU that controls starting and generating
modes of operation.
Refer to Starter/Generator Limitations, Section V, T.O. 1T-1A-1, for specific limitations of the
A 24-volt, 40 ampere-hour lead acid battery, located in the aft fuselage compartment, supplies
secondary electrical power for ground operation, engine starting, and emergency requirements.
Battery Switch and Relay
The battery switch placarded BATTERY, is located on the overhead switch panel. Switch
positions are labeled ON, OFF, and EMER.
The battery feeder protection unit energizes the battery relay, battery tie-in relay, and emergency
bus relay when the BATTERY switch is in the ON position. Placing the BATTERY switch to
the EMER position disengages the battery relay and battery tie-in relay, which isolates the
battery from the start bus.
Battery Feeder Protection Unit
The battery feeder protection unit detects any ground fault that may occur in the battery and
external power feeder and ground lines. If a ground fault occurs on the feeder line, the battery
feeder protection unit illuminates the red BATT FDR FAIL indicator on the overhead switch
External DC power is used for ground engine starts, battery charging, and maintenance requiring
electrical power. External DC power components consist of an external power receptacle,
located on the aft left side of the fuselage, and an external power relay located in the battery
power distribution box. The small key pin in the external power unit connector provides 28
VDC to the external power relay.
ELECTRICAL POWER SYSTEMS