Pressurization Flashcards
Where does pressurized air come from?
From the engines, bleed air
What position are the outflow valves if either engine is running below 85% N2 on the ground:
- Both outflow valves are fully open
- No pressurization while taxiing.
What happens to the outflow valves as soon as both throttles are pushed above 85% N2, before takeoff:
- Outflow valves start to slowly close
- This gently begins pressurizing the cabin to avoid pressure “bumps” during rotation.
The system doesn’t restrict the incoming air; instead it:
Controls how much air leaves through the outflow valves.
True/False; Inside the valves is a modulating diaphragm that moves to open or close the valves more or less.
True, The diaphragm’s position is controlled by air pressure behind it, this is what allows precise adjustments to cabin pressure.
Safety: Solenoid Controls cannot overpower 3 things:
- The pressure relief valves
- The cabin altitude limit valves
- The manual Cherry Picker valve
What is Isoberic mode?
A backup pressurization mode the system switches to automatically if it loses information from the air data sensor/computer, the part that normally tells the pressurization controller things like altitude and climb rate.
What is Isoberic mode logic?
“I don’t know where we’re going, but I’ll try to hold a constant cabin pressure that keeps passengers comfy and safe.”
Why does Isoberic mode switch to using Flight Levels instead of destination altitude?
Because it’s the best stable target the system can use without live air data.
“Okay, I can’t read how high we are right now, but if the pilot tells me our cruise FL, I’ll use that to hold a steady cabin pressure that gives us the best max differential without going over.”
In normal AUTO mode, the controller calculates a cabin pressure schedule using:
- Departure field elevation
- Current altitude (live from air data computer)
- Destination elevation (pilot input)
What is the primary role of the 23psi service air in the pressurization sysem?
Climb Mode:The pressurization controller sends the 23 psi air through a vacuum ejector to create suction, this pulls the diaphragm, opening the outflow valves.
Dive Mode: The 23 psi air is sent in directly as positive pressure behind the diaphragm. This pushes the diaphragm, closing the outflow valves.
What are the maximum scheduled rates of climb and descent for the digital pressure controller?
500/-600 fpm
The primary and secondary outflow valves are identical except:
-Primary valve has vacuum ejector
-Primary valve has cabin altitude climb and dive solenoids
The automatic mechanical feature releases outflow valve control chamber air as the cabin to outside air pressure differential reaches _____
8.5 +/- 0.1 psid
Maximum altitude limit valves prevent complete cabin depressurization above ______
13,000 ft
If we lost all DC power do we no longer have a way to pressurize or depressurize the cabin?
If we lose all electrical power, the automatic pressurization system fails, but we still have full manual pneumatic control of cabin pressurization using the Cherry Picker toggle valve. The manual system requires no electrical power
In the event of a total loss of DC power, why does the EMER Pressurization valve fail closed?
Why it fails closed:
* Emergency pressurization is only needed if primary pressurization fails in-flight.
* Fails closed to avoid unintentionally pressurizing the cabin with extremely hot, unconditioned windshield bleed air.
What is the normal maximum pressure differential for the Digital Pressure Controller?
8.3 psid
What is the maximum climb rate for the Digital Pressure Controller?
500 fpm
What is the maximum descent rate for the Digital Pressure Controller?
600 fpm
What cabin altitude does the Digital Pressure Controller maintain at 41,000 ft?
8,000 ft
What is the adjustable range for cabin altitude control?
2,000 - 14,000 ft
What inputs does the Auto Schedule of the Digital Pressure Controller use?
Inputs from air data sensor/computer
In the Auto Schedule, what does the pilot set regarding takeoff field elevation?
Destination + 200 ft
