Pressurization Flashcards
What type of air used to pressurize the cabin?
Bleed air
What unit controls the volume of bleed air and mixes it with ambient air to provide pressurization?
Flow control unit
What switches control the flow control unit?
The BLEED AIR VALVE switch
In what switch position is the flow control unit closed?
ENVIR OFF or INST & ENVIR OFF
What happens when the bleed air switches are OPEN?
Mixture of engine bleed air & ambient air flows through the FCU and through/around the air-to-air heat exchangers
Essentially, what does the flow control unit do?
Regulates the rate of air-flow to the pressure vessel
Where does the air flow out of the cabin after being used for cooling, heating, & pressurizing?
The outflow valve
What is the main purpose of the safety valve?
Provides pressure relief if the outflow valve fails, depressurizes the airplane if the CABIN PRESS switch is moved to DUMP, and keeps the plane unpressurized while it is on the ground with the left landing-gear safety switch compressed
What is the purpose of the negative-relief function?
Prevents outside atmospheric pressure from exceeding cabin pressure by more than 0.1PSI during rapid descents
When the plane is on the ground, why does only bleed air enter the cabin?
The safety switch causes the flow control unit to close a valve that lets ambient air mix with bleed air
When does ambient air begin to mix with bleed air?
After liftoff and the safety switch is depressed
After liftoff, the left flow control units ambient air valve opens, then the right flow control unit opens 6-8 seconds later. Why?
Pressure bumps are avoided by increasing the air flow volume gradually (left first, then right)
What controls the modulation of the outflow valve?
An adjustable pressurization controller
What knob controls the RATE at which the pressure altitude changes?
The rate control knob
The CABIN PRESSure switch has 3 positions: what are they?
DUMP, PRESS, TEST
What’s the position of the safety valve in the DUMP position?
Open, allows it to depressurize
What’s the position of the safety valve in the PRESS position?
Closed, pressurization controller takes command of outflow valve
What’s the position of the safety valve in the TEST position?
Closed, bypasses the landing gear safety switch to allow for tests on the ground
Prior to takeoff, how should the cabin altitude selector knob be adjusted?
To where ACFT ALT dial reads 500-1000ft above planned cruise pressure altitude
What’s the normal position for rate control knob?
9-12 o’clock
What are three reasons the airplanes altitude matches the cabins altitude?
Pilot forgets to set cabin altitude properly for landing.
Rate of climb was set too low on the pressurization controllers knob.
Descending at a much greater rate than usual.
What happens to differential pressure as the airplane descends?
It decreases - because the pressure inside and outside of the cabin decrease
What are 2 simple actions that will assure you will not “catch the cabin” during descent?
Set a sufficient rate of descent with the rate knob - 400/500fpm usually will work fine
Instead of waiting until descent to set pressurization for landing, make it the last item in cruise checklist. It is fine to run at max differential pressure.
