Pressurization

Question 1

What type of air used to pressurize the cabin?

Answer 1

Bleed air

Question 2

What unit controls the volume of bleed air and mixes it with ambient air to provide pressurization?

Answer 2

Flow control unit

Question 3

What switches control the flow control unit?

Answer 3

The BLEED AIR VALVE switch

Question 4

In what switch position is the flow control unit closed?

Answer 4

ENVIR OFF or INST & ENVIR OFF

Question 5

What happens when the bleed air switches are OPEN?

Answer 5

Mixture of engine bleed air & ambient air flows through the FCU and through/around the air-to-air heat exchangers

Question 6

Essentially, what does the flow control unit do?

Answer 6

Regulates the rate of air-flow to the pressure vessel

Question 7

Where does the air flow out of the cabin after being used for cooling, heating, & pressurizing?

Answer 7

The outflow valve

Question 8

What is the main purpose of the safety valve?

Answer 8

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

Question 9

What is the purpose of the negative-relief function?

Answer 9

Prevents outside atmospheric pressure from exceeding cabin pressure by more than 0.1PSI during rapid descents

Question 10

When the plane is on the ground, why does only bleed air enter the cabin?

Answer 10

The safety switch causes the flow control unit to close a valve that lets ambient air mix with bleed air

Question 11

When does ambient air begin to mix with bleed air?

Answer 11

After liftoff and the safety switch is depressed

Question 12

After liftoff, the left flow control units ambient air valve opens, then the right flow control unit opens 6-8 seconds later. Why?

Answer 12

Pressure bumps are avoided by increasing the air flow volume gradually (left first, then right)

Question 13

What controls the modulation of the outflow valve?

Answer 13

An adjustable pressurization controller

Question 14

What knob controls the RATE at which the pressure altitude changes?

Answer 14

The rate control knob

Question 15

The CABIN PRESSure switch has 3 positions: what are they?

Answer 15

DUMP, PRESS, TEST

Question 16

What’s the position of the safety valve in the DUMP position?

Answer 16

Open, allows it to depressurize

Question 17

What’s the position of the safety valve in the PRESS position?

Answer 17

Closed, pressurization controller takes command of outflow valve

Question 18

What’s the position of the safety valve in the TEST position?

Answer 18

Closed, bypasses the landing gear safety switch to allow for tests on the ground

Question 19

Prior to takeoff, how should the cabin altitude selector knob be adjusted?

Answer 19

To where ACFT ALT dial reads 500-1000ft above planned cruise pressure altitude

Question 20

What’s the normal position for rate control knob?

Answer 20

9-12 o’clock

Question 21

What are three reasons the airplanes altitude matches the cabins altitude?

Answer 21

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.

Question 22

What happens to differential pressure as the airplane descends?

Answer 22

It decreases - because the pressure inside and outside of the cabin decrease

Question 23

What are 2 simple actions that will assure you will not “catch the cabin” during descent?

Answer 23

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.