Specifications

SECTION II
MODEL 560 AIRPLANE AND SYSTEMS
An air cycle machine overheat sensor is installed between the compressor and turbine section of the
air cycle machine to prevent excessively hot air from causing damage to the air cycle machine due to
overheating. If this sensor indicates that the compressor section is producing air that is too hot
(approximately 435°F), it will close all shutoff valves in the bleed air ducts and open the emergency
pressurization valve when airplane is in flight. This will secure the air cycle machine and pressurize the
cabin by the emergency method. This condition will be indicated by the illumination of the EMERG PRESS
ON annunciator light as well as the increased noise level associated with high velocity air entering the
cabin. If the temperature drops below approximately 405°F within 12 seconds, the system will automatically
return to normal operation. If the temperature is not reduced within 12 seconds, it will be necessary to
rotate the pressurization source selector knob in the cockpit to EMER position and then reselect LH or RH
to reset the system for normal operation.
During high altitude operation, particularly at low airspeed and high power settings while attempting to
cool a warm cabin, it is possible for the cooling demand to exceed air cycle machine (ACM) capabilities.
This would result in ACM overtemperature and shutdown and automatically trip the EMERGENCY
pressurization on. To preclude this, an overtemperature protection circuit is incorporated which will bias the
temperature controller when the ACM compressor discharge temperature reaches approximately 405°F.
This bias causes the ACM temperature controller to respond as if a warmer cabin temperature had been
selected; therefore, it switches from cooling to heating mode until the ACM overtemperature condition is
corrected. Once the ACM compressor discharge temperature has cooled, the bias is automatically
switched out and the ACM will return to cooling mode. This system will cycle the bias in and out until the
ACM stabilizes (cabin temperature reaches selected value). The ACM overtemperature protection circuit
operates only in the AUTOMATIC temperature controller mode. Therefore, operations above 31,000 feet
altitude should be restricted to AUTOMATIC mode. It is possible, at high altitude, when using MANUAL
mode, to select a cold enough temperature to cause ACM shutdown and to trip the emergency
pressurization on.
A water separator is provided to dehumidify the conditioned air before entering the cabin. The
conditioned air enters the water separator where it is filtered and the excess water is removed. The
conditioned air is then ducted through a check valve into the cabin flow ducts for distribution. The
condensate is injected into the air flowing over the heat exchangers to increase cooling.
The cabin air distribution system consists of an overhead air duct and outlets, and underfloor and
armrest air ducts which supply conditioned air to the footwarmer manifolds, armrests, and the overhead
outlets. A separate cockpit and defog air distribution system is ducted forward through the underfloor from
a defog blower in the aft cabin.
When the air temperature selected is cold, a damper valve directs the air through the overhead, floor
and armrest air ducts. As the temperature selected becomes warmer, the damper valve will close,
recirculating underfloor airflow through the overhead air duct. When a hot temperature is selected (over
38°C (100°F), the damper valve will be closed, which directs all hot airflow through the floor and armrest air
ducts.
A flow divider is provided to allow the crew to proportion, to a certain extent, the amount of air
provided to the cockpit versus the cabin. The flow divider does not affect the overhead outlet system. A
five-position selector is provided on the tilt panel for control of the flow divider.
Switches labeled OVHD FAN and DEFOG FAN are located on the copilot’s panel. Both have
HI/OFF/LOW positions. If increased air circulation is desired, position the OVHD FAN switch to the HI or
LOW position. This actuates the cabin fan, increasing airflow through the overhead ducts. The DEFOG
FAN switch controls defog and ventilation airflow into the flight compartment.
I 56OMB-01 Configuration AA 2-55