The cooled bleed air flowing out the heat
exchanger core is ducted back to the bypass
side of the H-valve where it mixes with hot
bypassed bleed air. The resulting conditioned
air is then directed into the cabin and cockpit
distribution system.
When the airplane is on the ground,
do not perform extended engine
operation above idle with the CAB
AIR and AIR BLEED switches
positioned to ON. Since there is no
ram air for cooling of the bleed air,
possible damage to the air-condi-
tioning components could result.
Damage might also occur to interior
cabin furnishings, as well as over-
heating the tailcone area.
Ram-Air Ventilation
In the event that the airplane is unpressurized
in flight, air for circulation and ventilation of
the cabin and cockpit areas is provided by ram
air, which is ducted into the conditioned bleed-
air distribution system.
During normal operation, a one-way check
valve in the connecting ram-air duct prevents
loss of conditioned pressurization bleed air
though the ram-air plenum exhaust port.
Cabin and Cockpit
Air Distribution
General
Conditioned airflow distribution to the cabin
and cockpit areas is essentially the same for
all airplanes (see Figure 11-2). The condi-
tioned air is routed from the tailcone into the
cabin area through two ducts, one on each
side of the cabin. The left duct ends at the
entry door, and the right duct continues
forward to the cockpit.
Cabin Air Distribution
Cabin air distribution is furnished by diffusers
installed at intervals along the two ducts, and
they direct airflow toward the floor.
A one-way air distribution check valve is
located at the aft end of each cabin duct. These
valves are functionally related to the pres-
surization system, as described in Chapter 12
of this manual.
On SNs 24-350 and subsequent and 25-227 and
subsequent, distribution of air changes when
either or both emergency pressurization valves
are positioned to emergency.
If only one emergency valve is positioned to
emergency, all bleed air from that engine is
routed directly into only that side’s cabin dis-
tribution duct, and temperature control of that
air is lost. However, bleed air from the oppo-
site engine is still subject to the normal con-
ditioning process. One-way check valves in the
normal distribution ducting prevent the emer-
gency airflow from being lost through the nor-
mal distribution system.
If both emergency valves are positioned to
emergency, all bleed air from both engines is
routed directly into the respective left and
right distribution ducts. Temperature control
is then sacrificed for pressurization.
Cockpit Air Distribution
Cockpit air distribution is provided by duct-
ing connected to the forward end of the right
cabin duct. Outlets located on the sidewall
panels and adjacent to the outboard rudder
pedals enable the pilots to control and direct
the airflow as desired. A footwarmer diffuser,
located below the instrument panel just for-
ward of the center pedestal, directs continu-
ous conditioned air along the center floor.
Two piccolo tubes installed vertically on each
side of the windshield center support structure
direct a continuous flow of conditioned air
across the forward section of each pilot’s wind-
shield for interior windshield defogging.
CAUTION
11-5
FOR TRAINING PURPOSES ONLY
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