STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS
Pressurization control subsystem
Electric Heat Subsystem (EHS)
The VCCS provides preflight, in-flight, and postflight air conditioning for the flight deck and
avionics rack exhaust.
The VCCS is the only source of cooling when the aircraft's engines are not operating. It is also
the backup cooling source when the ACU is not operational. The VCCS operates on 28 VDC
external ground power when the engines are not operating and the right nonessential bus when
the engines are operating.
VCCS Controls and Indicators
The AUX TEMP CONTROL switch group on the environmental control panel controls VCCS
AUX COOL - Supplies electrical power to the VCCS compressor.
GND AIR - Supplies electrical power to the fresh air blower motor when the landing gear
pump and solenoid valve to open the outflow safety valves.
AV STBY BLO - Supplies electrical power to the avionics rack refrigerant shutoff
solenoid valve when the AUX TEMP CONTROL switch is in the AUX COOL position. The
valve deenergizes, stopping refrigerant flow to the avionics rack evaporator. In this condition
flight deck cooling is maximized.
ACU is capable of maintaining the cabin temperature between 60-90 degrees Fahrenheit (F) at
all ambient temperatures up to and including the service ceiling.
ACU Controls and Indicators
Reference the ACU diagram in the T.O. 1T-1A-1.
Bleed Air Selector
OFF - Ram air is supplied to the cabin in flight. VCCS cooling air is available, bleed air is
ENVIRONMENTAL CONTROL SYSTEMS 7-3