Pneumatics, Air Conditioning, Pressurization Flashcards
What systems onboard are powered with bleed air?
Air conditioning system, pressurization system, rudder bias system, hydraulic reservoir pressurization, and engine anti-ice
What does the Mixing Valve do, and when is it activated?
Provides a boost to the (Low Pressure) bleed air system with High Pressure air when the MAIN AIR VLV switch is in the OPEN position and pressure drops below 27 psi
What are some scenarios in which the Mixing Valve would activate?
Low engine power scenarios, such as descent and landing
What does the PRSOV do?
The Pressure Regulating Shut-Off Valve steps down bleed air before reaching the air cycle machine to protect it
Where can emergency pressurization and heat come from onboard?
Engine No.2 bleed air
What are the positions of the main air valve?
- CLOSE: MAV and HP valve both closed
- LP ON: MAV open, HP valve closed
- OPEN: MAV open, HP valve armed
Why are the main air valves time delayed? What are the delays in seconds?
Time delayed in order to prevent surging of pressurization system.
- MAV 1: takes 20 seconds to fully open
- MAV 2: opens in 1 second, but delayed by 30 seconds when commanded to open
What powers the main air valves, HP valve, and HP AIR OVHT annunciators?
PE bus
What are the limitations of the main air valves?
MAVs must be closed prior to takeoff and landing
During single-engine operations in icing conditions, select LP ON on operating engine to ensure sufficient HP air for engine anti-ice
What do the MAIN AIR VALVE annunciators indicate?
On the ground: MAVs are open while aircraft is weight on wheels (on the ground)
In Air: MAV is not in the selected position (closed) (time delay of 50 seconds)
What is the function of the air cycling machine?
Cools bleed air, removes excess water in the system before ducting to flight deck and passenger cabin
What is the low-limit temperature?
Temperature of air at water separator inlet limited to 6°C to prevent freezing; warm air from primary heat exchanged routed through low-limit temperature control system to warm if needed
When does the DUCT OVHT annunciator illuminate?
When cabin air duct temperature exceeds 116°C; causes cabin temp control valve to close
What are the two modes for the cabin temperature control system?
AUTO: Cool/Hot selector allows temperature selection between 65°F and 88°F, temperature control valve automatically adjusted
MANUAL: selector clicks into manual position and becomes toggle switch between COOL and HOT; extreme temperature limiting sensor activate (6°C to 116°C)
What does the CABIN FLOOD switch do?
Opens valve for temperature controlled air to enter cabin in right rear of cabin at roof level
What does the CABIN FAN switch do?
Controls electrically operated fan to recirculate cabin air to individual outlets at each passenger seat
What does the CABIN FLOOR switch do?
Opens valve to allow temperature controlled air to enter floor outlet ducts
What does the F/DK VLV switch do?
Allows variable supply of hot air into the flight deck area; automatic overheat protection closes valve at 115°C
What is ram air used for in the air conditioning system?
Cools heat-exchangers and ventilates unpressurized cabin; also ventilates rear equipment bay
Besides the engines, what else can supply air conditioning to the cabin?
The APU on the ground or in-flight
What is a major limitation regarding bleed air?
Simultaneous operation of APU bleed air and main engine bleed air limited to one minute during bleed changeover
How do we control cabin pressure?
By the amount of air we let OUT of the cabin
What does the cabin triple indicator indicate?
- Pointer: cabin altitude
- Unmarked Pointer: indicated rate of change
- Red and White Pointer: pressure differential
What does the cabin controller knob do?
Used to set desired cabin altitude and rate of change
What does the outflow/safety valves do?
Allows controlled outflow of cabin air
What does the vent valve do?
Allows air to exit the cabin - can be used to clear smoke, will depressurize cabin
What are the pressure regulators in the pressurization system, and when do they activate?
Safety devices that shut both outflow valves if cabin altitude reaches 13,500’ ± 1,500’
When does the CABIN ALTITUDE warning go off?
Annunciator and horn sound at cabin altitude of 9,300’ ± 300’; horn can be inhibited with flaps selected greater than 15
Cabin altitude warnings rescheduled to 14,000’ ± 300’ if the CABIN HIGH DATUM switch is selected
How is the cabin altitude selector set in flight?
Outer ring: cabin altitude
Inner ring: cruise altitude
For cruise altitudes of 25,000’ or more, select cruise altitude plus 2,000’
For cruise altitudes lower than 25,000’, set 2,000’ above departure airport altitude
For landing, set outer scale to airport elevation plus 0-400’ depending on altimeter setting
N1PU Setting Field
https://ibb.co/nLf8fxH
What is the cabin altitude at FL410?
7,500’
What is the maximum pressure differential?
8.55 PSID
What is the overpressure condition for the pressure differential?
8.6 - 8.8 PSID
What is the maximum negative pressure differential?
-0.5 PSID
What is the cabin limiter altitude?
13,500’ ± 1,500’
What altitude sounds the cabin high ANC/horn?
9,300’ ± 300’
What altitude sounds the cabin high ANC/horn in high datum mode?
14,000’ ± 300’
The HP bleed air supplements the LP bleed air at the mixing valve when both main air valves switches are selected to OPEN and:
LP bleed-air pressure drops to 27 psi
Prior to takeoff and landing, ensure that the flight deck valve and the main air valves are set to the _____ position.
CLOSE
This occurs when a main air valve switch is moved from the CLOSE position to the LP ON position:
The main air valve opens, but HP air augmentation is not allowed
The position of the MAIN AIR VLV 1 or 2 switch in which electrical power is applied to a pressure switch is:
OPEN
When placed in the “open” circuit, The No.1 MAV has a time delay of approximately _____ before it reaches the fully open position.
20 seconds
Which component in the air conditioning system determines the temperature of the air after entering the water separator?
Low-limit temperature control
When the duct temperature limiter senses a duct temperature of 116°C:
The limiter illuminates the DUCT OVHT ^ annunciator and automatically gives reduction in duct temperature
Cabin delivery air temperature is controlled by operation of the:
Cabin temperature control valve
A pressure switch downstream of the PRSOV protects the ACM from overspeed if pressure rises above:
40 psi
When too much air pressure is present, the 40-psi pressure switch protects the ACM from overspeed by closing:
The No.2 main air valve
The switch that controls the auxiliary heating valve to provide additional heating to the cockpit is the:
F/DK VLV switch
The _____ bus powers the CABIN TEMP - MANUAL mode.
PE
The pressurization system is capable of maintaining a cabin altitude of 7,500’ when the airplane altitude is:
41,000’
The pressurization system can maintain a maximum cabin differential pressure of:
8.55 psi
The maximum allowable negative cabin differential pressure is:
-0.5 psi
The fan-operated venturi provides suction to open:
Both outflow valves
With the CABIN HIGH DATUM not selected, the CABIN ALTITUDE warning annunciator illuminates and the warning horn sounds at _____ feet.
9,300’ ± 300’
