Pressurization

Question 1

Pressure

Answer 1

Pressure decreases as Altitude increases

Temperature decreases as Altitude increases
●-2 degrees Celsius per 1000’ gained

Question 2

Sealed cabin

Answer 2

High altitude/space flight
Oxygen is circulated and filtered

Question 3

Pressurized cabin

Answer 3

Forces ambient air into the cabin

Question 4

Pressurization terms

Answer 4

Cabin Altitude – air pressure inside the cabin
●Ex: Cabin Altitude is 8000ft (MSL)

Cabin Differential Pressure – the difference between the air pressure inside the cabin and the air pressure outside the cabin.
●Cabin Pressure – Ambient Pressure = CDP

Cabin Rate of Climb – the rate of change of air pressure inside the cabin (fpm).

Question 5

Pressurization requirements

Answer 5

Be able to maintain a cabin pressure of 8000’ or lower, regardless of cruising altitude
Be able to prevent rapid changes of cabin pressure
Circulate air from inside to outside to eliminate odors and remove stale air
Be able to produce comfortable temps inside the cabin

Question 6

A pressurized cabin must have

Answer 6

●Air tight Seal
●Cabin structure
●Source of compressed air
●Temperature regulation
●Pressure regulation

Question 7

Cabin structure

Answer 7

A structure strong enough to withstand forces in flight plus act as a pressure chamber.
●Doors
●Windows
●Control cables
●Electrical wires
•Must also be light weight

Question 8

Source of air pressure

Answer 8

Reciprocating Engines
●Turbocharger
●Supercharger
●Engine Driven Compressor
Independent compressor for pressurization

Less air available for engine when used for cabin pressure

Question 9

Turbine engine

Answer 9

Turbine’s purpose is to compress large amounts of air to be mixed with fuel and burned
Provides a great source for uncontaminated air

Types:
●Jet Pump
●Turbo Compressor
●Air Cycle Machine

Question 10

Jet pump

Answer 10

Bleed air goes into a Venturi Pump
Low pressure from venturi also brings in outside air
Air is mixed and used to pressurize

Question 11

Turbo compressor

Answer 11

Bleed air drives a separate compressor
Outside air is drawn in and compressed
Air is mixed and used to pressurize aircraft
●Usually found on turboprop aircraft

Question 12

Air cycle machine

Answer 12

Bleed air turns turbine
Air is compressed and then allowed to expand and cool
Bypass air is mixed back in to control temperature

Question 13

Isobaric pressure control

Answer 13

Maintains the set Cabin Altitude at a single pressure as the aircraft changes altitude
●Ex: Flight crew will set cabin altitude at 8000’ (10.92 psi)
●Pressure is established at 8000’ and remains constant as aircraft altitude fluctuates

Question 14

Differential pressure control

Answer 14

Constant differential pressure is kept by controlling cabin pressure to maintain a pressure difference between the air inside the cabin and ambient air outside the cabin
●Pressure remains lower than max differential pressure which would cause airframe damage

Question 15

Automatic mode

Answer 15

●Cabin pressure is maintained automatically via the outflow valve which is modulated to maintain pre-programmed cabin altitudes.
●Specific aircraft configuration will cause the outflow valve to open. (Weight on Wheels switch)
●Takeoff abort mode allows the cabin pressure controller to remember the takeoff altitude in case a RTF is required.

Question 16

Manual mode

Answer 16

●Turns OFF the cabin pressure controller
●Enables manual control of the outflow valve
Remember
●In this mode the pilot changes the differential pressure to produce a specific cabin altitude.
●Differential pressure goes UP, cabin altitude goes DOWN.

Question 17

Dump mode

Answer 17

●Used to remove ALL pressurization
●Opens the outflow valve
●Maybe required if the maximum differential pressure is exceeded

Question 18

Emergency smoke removal

Answer 18

●Forward safety valve may be used to remove smoke from the cockpit.
●Emergency Ram Air ventilation may be used to remove smoke from the aircraft cabin.

Question 19

Ground ops

Answer 19

Ground source is used to reduce cost/mx of running the engine or using the APU while boarding

Air is still distributed using the same distribution process

Question 20

Slow leaks

Answer 20

Popping of ears & mild hypoxia
May be insidious with incapacitation occurring gradually
Master Warning-Triggered at 9,800ft
Drop down masks will drop automatically at 14,000ft

Question 21

Rapid

Answer 21

Occur suddenly and without warning.
Loud noises, flying debris, sudden temperature drop, fogging…
Must perform memory procedures quickly and accurately

Question 22

Explosive

Answer 22

Total loss of pressurization in less than 1 second
Rate of pressure change exceeds the lung’s ability to off gas
May injure pilots and passengers