AIR CONDITIONING General Pressure regulated engine bleed-air is cooled and temperature regulated in two air conditioning packs. The temperature-regulated airflow can be mixed with recirculated cabin air. Cabin and flight deck are supplied with conditioned air from the corresponding pack. Excess airflow from the flight deck pack is added to the conditioned air from the cabin pack. The capacity of one air conditioning pack is sufficient for all air conditioning and pressurization requirements. Additional flight deck heating is available when one air conditioning pack is switched OFF. Air conditioning packs Controls and indicators are located at the AIRC ONDITIONING panel. Depending on system configuration an additional cabin temperature controller is located at the cabin attendant panel. Air supply Airflow to both air conditioning packs is controlled by pressure regulating/shut-off (PR/SO) valves. See BLEED-AIR SYSTEM. Bleed-air is admitted to the air conditioning packs via the pack shut-off valves. These valves are normally open. The valves close in any one of the following conditions: PACK push button in OFF position. Insufficient upstream pressure. Pack overheat the overheat signal will retain, after the temperature has dropped, until the pack is manually switched OFF. Temperature control General Two independent systems, one for the flight deck and one for the cabin, automatically maintain the selected temperature by adjusting the temperature control valve. Automatic and manual control of these valves is provided via the temperature selectors. For aircraft equipped with cabin temperature authority pushbutton The temperature in the cabin can be controlled from the attendant panel, To control the cabin temperature from the flight deck, the CABIN TEMP AUTHORITY pushbutton has to be depressed. Recirculation Cabin air is supplied to the mixer in the air conditioning packs by two recirculation fans; one for each pack. The fans are controlled with the RECIRC push buttons. When the flight deck pack shut-off valve is closed, the corresponding fan cannot be activated. Page 1
DISTRIBUTION Outlets Conditioned air for the flight deck is routed to floor, sidewall, and ceiling outlets, to window demisters, and adjustable louvres. The window demisters can be opened with the WINDOW DEMISTING handle located at the RH side panel. The floor outlets can be opened with the LH and RH FLOOR VENT handles, located at the side panels. The ceiling outlets can be opened with vent handles which are located above the flight deck entrance. Conditioned air to the cabin is distributed along both sides of the compartment. Electrical heating Air to floor outlets, sidewall outlets, and window demisters can be heated electrically when one air conditioning pack is switched OFF. The heater is switched ON with the FLIGHT DECK HEATER push button. Ground ventilation An external supply of conditioned air can be connected to the aircraft for distribution to the flight deck and the cabin. Ram air ventilation Two manually operated fresh air scoops for ventilation during non-pressurized flight are installed flush with the fuselage, one below each sliding window. The scoops can be selected OPEN with the FRESH AIR SCOOP levers, which are located above the LH and RH side panels. A check valve prevents ventilation when the aircraft is pressurized. Page 2
Functional diagram Page 3
Controls and indicators Controls and indicators - Type I Page 4
Controls and indicators - Type II Page 5
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Alerts CONDITION(S) / LEVEL AURAL MWL/MCL CAP LOCAL RECIRC RECIRCULATION FAN FAILURE 1 FAULT PACK PACK SOV CLOSED 1 FAULT PACK FAULT BOTH PACK SOV CLOSED 2 CAUTION PACK FAULT Page 8
PRESSURIZATION General Pressurization is obtained by an automatic system, which controls the outflow of conditioned air. Controls and indicators of the pressurization system are located at the pressurization panel. A cabin rate/cabin altitude/differential pressure indicator is installed next to the pressurization panel. The maximum pressure differential (5.45 psi) allows a cabin altitude of 8.000 feet at a flight altitude of 25.000 feet If the cabin altitude exceeds 10.000 feet, a CABIN ALT light at the CAP illuminates. Manual pressurization control is possible. Pressurization control Automatic On the ground, with the POWER levers not in TO position, the outflow valves are commanded to be fully open. In flight, the controller issues commands to the outflow valves until the actual cabin altitude equals the computed altitude. The computed altitude is determined by the controller, based on crew selections of landing field altitude, barometric pressure, and rate of change limit. The controller limits the differential pressure to a preset value (5.45 psi). When the automatic controller fails, a FAULT light illuminates. Outflow valves Two outflow valves are used to control cabin pressure as dictated by the pressurization controller. Each outflow valve has provisions to limit maximum pressure differential. The differential limit is set slightly higher than the preset value of the controller. Manual If the automatic controller fails, control of the outflow valves is automatically reverted to the manual control mode. The manual control mode permits the crew to vary the cabin altitude UP or DOWN at a selectable rate of change or to keep the cabin altitude at a desired level. With the manual pressure control lever in UP, full depressurization can be accomplished. After depressurization, the outflow valves remain open. The rate of depressurization is controlled with the manual RATE of change selector. Manual control can also be obtained by depressing the PRESS CONTROL push button to MAN. When depressed to MAN after a failure of the automatic system, the FAULT light goes out. Page 9
Functional diagram Page 10
Controls and indicators Page 11
Alerts CONDITION(S) / LEVEL AURAL MWL/MCL CAP LOCAL PRESS CONTROL AUTOMATIC PRESSURIZATION CONTROLLER FAILURE 2 CAUTION FAULT CABIN ALTITUDE IN EXCESS OF 10.000 FT 3 WARNING CABIN ALT Page 12
SYSTEM OPERATION Air conditioning Automatic temperature control Before engine start set temperature selectors at approximately mid position (twelve o clock). After take-off monitor cabin temperature and adjust in small steps as necessary. Manual temperature control If the temperature is not satisfactorily controlled automatically, use manual temperature control. Set and hold temperature selector in cold or hot as required for approximately five seconds. After a while check effect on temperature display and adjust in small steps as required. Page 13
Pressurization Automatic control Before flight: Set field elevation. Check rate limit selector on mark. Set baro at QNH (altimeter setting). Manual control Before flight, determine cabin altitude according to table. CRUISE LEVEL 100 120 140 160 180 200 220 250 Target cabin altitude 0 0 1000 2500 4000 5000 6500 8000 Select PRESS CONTROL pushbutton to MAN. Set manual rate control to DECR. After take-off: Set manual pressure control lever to UP. At the required cabin altitude set manual pressure control lever to center position. Use manual rate control as required. Before descent: Set manual pressure control lever to DN. When the cabin is at the field elevation, set manual pressure control lever to center position. Use manual rate control as required. CAUTION: In order not to overshoot the required cabin altitude or field elevation, closely monitor the cabin altitude during climb or descent. Recirculation Recirculation fans are always on to augment the air conditioning flow, but when an external air conditioning unit is used switch the fans off. Economy ECONOMY may be selected at cruise altitude if the number of passengers is small. During take-off the system switches to ECONOMY to reduce bleed-air off take. After take-off the system returns to the selected position. If an engine fails or is shut down below 10000 ft altitude the system will shut off when operating at high engine power. Above 10.000 ft the system will switch to ECONOMY. Page 14
System data Cabin altitude At maximum aircraft altitude of 25.000 ft the cabin will be at 8000 ft and the pressure differential is 5.5. psi. Cabin rate of change (Approximately) Automatic Climb Rate limit selector: Normal on mark 550 ft/min Minimum 0 ft/min Maximum 2500 ft/min Automatic Descent Rate limit selector: Normal on mark 350 ft/min Minimum 0 ft/ min Maximum 1575 ft/min Page 15