Operation Manual Part 2

Aerosoft – Digital Aviation
CRJ-70 & CRJ-900
AOM PART 2
Systems Description
VOL
5
5-1-25
26-Jul-2017
BACKUP TUNING UNIT
The backup tuning unit provides a spare / backup in case both RTUs fail. Normally the backup tuning unit stays
in standby mode the entire flight. As soon as it is switched on it takes control of COM1 and NAV 1.
1. RTU INHIBIT: Disables either RTU
2. FREQUENCY DISPLAY: Shows COM1
(upper) and NAV1) lower, TX is displayed
to indicate transmission
3. TUNING SELECTOR: Toggles between
tuning COM1 and NAV1
4. FMS TUNE INHIBIT: Stops FMS Autotune
function
5. ATC SEL: To select the active transponder
6. MODE SELECTOR:
a. OFF: Display off
b. STB: Displays the frequency shown in RTU1
c. ON: Frequency is controlled by the tuning knob
d. SQ OFF: Squelch selected off
7. TUNING KNOB: To set frequency
ELECTRICAL
The CRJ’s electrical system can be split into an alternating current, AC, subsystem and a direct current, DC,
subsystem. The alternating current, AC system is supplied with power from the engine generators (integrated
drive generators, IDGs), the auxiliary power unit’s generator or the air driven generator, ADG (which is a
backup in case both IDGs fail). The direct current, DC, system is supplied with power from two transformer
rectifier units, TRUs, the main battery, or the APU battery. The TRUs convert alternating current to direct
current. To reload both batteries, battery chargers are installed as well.
Both subsystems use computers to ensure the proper power distribution to the respective systems. The
following table shows the available AC and DC busses.
AC busses
DC busses
• AC BUS 1
• AC BUS 2
• AC ESSENTIAL BUS
• AC SERVICE BUS
• ADG BUS
• DC BUS 1
• DC BUS 2
• DC ESSENTIAL BUS
• DC SERVICE BUS
• DC BATTERY BUS
• DC EMERGENCY BUS
• DC UTILITY BUS
• MAIN BATTERY DIRECT BUS
• APU BATTERY DIRECT BUS
Furthermore – when on ground – an external power receptacle is available which allows the CRJ to be supplied
with ground power. The electrical power panel on the overhead panel is used to control the electrical systems.
Error messages, warning or advisories are indicated on the EICAS.