DC power distribution (see FO-7 and fig. 1-16)

STUDENT GUIDE T-39N/G NATOPS

B. DC power distribution (see FO-7 and fig. 1-16).

1. Starter bus - powered by external power or batteries in series. Minimum of 24v before

battery start/ 12v during battery start.

2. Battery bus - Can power the paralleling, essential, or start bus.

3. Paralleling bus

In flight, powered by generator(s) {will automatically disconnect with a Dual Gen Fail}. On

deck, powered by external power, batteries, or generator(s). Can power all buses except the start bus.

Powers the hydraulic pump. Remains powered in Dual Gen Fail condition if in T-39G.

4. DC essential bus

a. Powered by paralleling bus.

b. Powered by batteries if dual gen failure in flight.

5. DC secondary bus

a. Energized by the paralleling bus on deck, only if both DC generators are online or

external power is applied.

b. In flight, powered by paralleling bus with either DC generator online (no power if dual

gen failure).

6. T-39N only - DC mission bus A and B (DC MISSION PWR switch)

a. Powered by DC essential bus.

b. Bus A supplies power to the radar inverters and mission essential equipment. Should bus

A overload, the Mission Bus A circuit breaker will trip causing the MISSION A FAIL

annunciator light to illuminate.

c. Bus B powers cabin non-essential loads. Note: see fig 1-17(sheet 10 of 10 for BUS A/B

power distribution)

d. Should either generator fail with both buses energized normally, load shed of both A & B

buses will occur. Moving the Mission Power Switch to EMER restores power to bus A

and radar only. Should both generators fail, load shed of both buses will occur and they

will remain shed.

C. DC power controls

1. Electrical Master switches: guarded ON, allows the battery switch to function and the

generators to power the paralleling bus.

2. Battery switch:

a. ON - connects the battery bus to paralleling bus (allows automatic transfer to ESS bus in

the event of a dual gen fail; parallel bus taken off line).

3-2

ELECTRICAL SYSTEM