STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS
ELEC HEAT 1 AND 2 - Supplies power to electric heater number one and three in the air
distribution ducts supplying the flight deck side window defog outlets, windshield defog outlets,
flight deck floor outlets, and the aft evaporator blower motor. In addition, it supplies power to
electric heater number two in the duct supply to the glareshield outlets.
AUTO FLDK - ACU uses flight deck and duct temperature sensors to automatically
maintain cabin air temperature at the temperature set by the COLD HOT (temperature selector)
AUTO DUCT - ACU compares duct temperature to that set by the COLD HOT control
and maintains duct air temperature to selected value.
MAN DUCT - Opens or closes cabin temperature control valve to maintain cabin
temperature set by COLD HOT control.
Pressurization Control Subsystem
Bleed air supplied for heating and cooling is also used to pressurize the cabin. The cabin is
pressurized by air flowing from the flight deck and cabin air outlets. The pressurization system
uses a variable isobaric controller to open and close two outflow safety valves through a
pneumatic relay. Either one or both outflow safety valves open and close automatically, as
required, to provide positive or negative pressure relief protection. The cabin altitude pressure
regulator directly senses cabin pressure. When the cabin altitude reaches 12,500 + 1500 feet,
poppet valves in the regulators open to direct cabin pressure to both outflow safety valve control
Pressurization Control Subsystem Controls and Indicators
Cabin Pressure Low Annunciator - Illuminates when cabin altitude exceeds 9500 + 500
Cabin Pressure High Annunciator - Illuminates when cabin pressure differential exceeds
9.1 + 0.1 psi.
Cabin Controller - The cabin pressurization controller placarded CABIN CONTROLLER
(mounted on the CP's instrument panel) controls the cabin altitude and rate of climb. The small
knob (located in the lower left portion of the cabin controller) controls cabin altitude rate of
change within a range of approximately 50-2000 Feet per Minute (FPM).
Manual Pressurization Control - The manual pressurization control, placarded
MANUAL PRESSURIZATION, is located on the environmental control panel. The cabin is
manually depressurized in case of an emergency by turning the valves knob seven complete
revolutions, counterclockwise. The cabin may be depressurized to a maximum of 12,500 + 1500
ENVIRONMENTAL CONTROL SYSTEMS 7-5