AIR CONDITIONING AND PRESSURIZATION
Description
Aircraft Operations Manual
2.1
PAGE
4
Jun 01/18
The heaters are powered from the UTILITY BUS
and are individually controlled by an ON
−
OFF
switch on each side panel.
Optional cargo heater installation. Mod. No. 2787
option 21:07
To improve the temperature in the normally non
heated cargo compartment an optional electrical
cargo heater can be installed.
The heater consists of an AC driven heater and a
DC driven fan for air circulation. The heater unit is
controlled from a dedicated CARGO HEATER ON
−
OFF switch in the cockpit. To operate, the cargo
heater requires both AC generator to be on line,
and is accordingly automatically disconnected if ei-
ther AC generator drops off line. Further more the
heater unit is disconnected if the cargo fire extin-
guisher is activated.
With the system in operation the temperature in the
cargo compartment will be kept at m2
C at
OAT
−
60
C and +12
C at OAT
−
40
C. The temper-
ature in the cargo compartment can be continuously
monitored by the TEMP indicator on the overhead
panel.
2.2
Pressurization system (Fig. 4)
The cabin is pressurized by both air conditioning
packs. The pressure is regulated by two outflow
valves, located in the empennage.
The primary outflow valve is electro
−
pneumatically
controlled by a pressurization controller and is nor-
mally used for automatic pressure regulation. The
secondary outflow valve is pneumatically controlled
from the cockpit control panel and is used as a
manual standby system. Both outflow valves are
supplied with servo vacuum pressure from the
pneumatic system.
The outflow valves also incorporate positive and
negative relief functions. For relief valve opening,
maximum positive differential pressure is 7.6 psi
and maximum negative pressure is 0.5 psi.
In the corporate version an additional altitude limit
control function is added on the electro
−
pneumatic
primary outflow valve preventing cabin altitude to
exceed 15 000 ft should the pressurization control-
ler fail.
For emergency pressure relief, the electro
−
pneu-
matical outflow valve can be opened by an emer-
gency pressure dump switch. With Mod. No. 1994
installed both outflow valves are opened with the
pressure dump switch when on ground.
For maintenance purpose the system can be
switched to flight mode on ground using the CAB
PRESS switch in the overhead TEST 2 panel.
Automatic operation
When the system is in AUTO and powered, a pres-
sure controller self
−
test is initiated. This illuminates
a FAULT light on the control panel. If no fault is de-
tected, the light will go off in less than 3 seconds.
The automatic function of the pressurization system
works in six different modes depending on phase of
flight:
−
Ground mode
The system is in ground mode
when the aircraft is on ground with power levers
retarded.
Without Mod. No. 1994 installed:
After engine start, vacuum pressure is supplied
to the outflow valves which will go to fully open
position.
With Mod. No. 1994 installed:
After engine start, vacuum pressure is supplied
to the outflow valves which will make the primary
electro
−
pneumatic valve to go to fully open posi-
tion while the secondary pneumatic valve re-
mains closed (the valve is closed during all nor-
mal operation).
−
Pre
−
pressurization mode
When one power le-
ver is moved above the minimum takeoff power
position (64
power lever angle), the system
transfers to pre
−
pressurization mode.
Without Mod. No. 1994 installed:
The secondary pneumatic outflow valve will close
and the primary electro
−
pneumatical outflow
valve is modulated towards its closed position
permitting cabin pressurization at a rate of 300
ft/min (at detent position) to 140 ft below actual
cabin altitude existing prior to power levers ad-
vancement. If both power levers are retarded
below the min. takeoff power position the secon-
dary pneumatic outflow valve will go to fully open
position and the primary electro
−
pneumatic valve
modulates a cabin uprate of 500 ft/min. After 20
