Pressurization

Question 1

Pressurization Rate for the mix of bleed air from engines and ambient air is approx:

Answer 1

A mixture of bleed air from the engines and ambient air is available for pressurization to the cabin at a rate of approximately 10 to 17 pounds per minute.

Question 2

Approximately what % N1 is required for normal pressurization?

Answer 2

Approximately 75% N1 is required for normal pressurization, 85% if single engine.

Question 3

What component controls bleed air from the engine and makes it usable for pressurization by mixing the bleed air with ambient air?

Answer 3

The Flow Control Unit

Question 4

How are excessive pressure bumps mitigated during takeoff?

Answer 4

On takeoff excessive pressure bumps are mitigated by landing gear safety switch actuated solenoids incorporated in the flow control units.

Question 5

How do the landing gear safety switch actuated solenoids stage the input of ambient air flow?

Answer 5

Through a time delay, input of ambient air flow introduction is first through the left flow control unit, then 4 seconds later air flow through the right control unit.

Question 6

C Model Pressure Vessel is designed for a normal working pressure differential of?

Answer 6

C Model Pressure Vessel is designed for a normal working pressure differential of 6.0 psi which provides a cabin altitude of 3870 at an aircraft altitude of 20,000 feet.

Question 7

What occurs when the PRESS DUMP/PRESS/TEST switch is held to the DUMP position?

Answer 7

In the DUMP position, the safety valve will be opened and the cabin will be depressurized to the aircraft altitude.

Question 8

What occurs when the PRESS DUMP/PRESS/TEST switch is held to the TEST position?

Answer 8

In the TEST position the landing gear safety switch is bypassed to enable testing of the pressurization system on the ground.

Question 9

Explain the difference between the long and short needles in the Cabin Altitude Indicator.

Answer 9

The longer needle indicates aircraft altitude in thousands of feet on the outside dial, the shorter needle indicates pressure differential in psi on the inner dial.

Question 10

What two valves are located on the aft pressure bulkhead?

Answer 10

Outflow Valve and Safety Valve

Question 11

What is the job of the Outflow Valve?

Answer 11

The Outflow Valve is pneumatically operated and maintains the selected cabin altitude and rate of climb as commanded by the cabin altitude and rate of climb controller.

Question 12

How does the Outflow Valve work basically?

Answer 12

As the aircraft climbs the controller modulates the outflow valve to maintain a selected cabin rate of climb and increases the cabin differential pressure until maximum pressure differential is reached.

Question 13

What cabin altitude will trigger the warning light ALT WARN?

Answer 13

At a cabin altitude of 12,500 feet a pressure switch mounted on the back of the overhead control panel completes a circuit to illuminate the ALT WARN warning light.

Question 14

What is the state of the Safety Valve before takeoff?

Answer 14

Before takeoff the Safety Valve is OPEN with equal pressure between the cabin and outside air. The Safety Valve CLOSES on lift off if the Cabin Press Dump switch is in the PRESS mode.

Question 15

Purpose of the Safety Valve?

Answer 15

The Safety Valve provides pressure relief in the event of a failure of the Outflow Valve.

Question 16

Additional purpose of the Safety Valve?

Answer 16

The Safety Valve is also used as a dump valve and is opened by VACUUM which is controlled by a solenoid valve operated by the Cabin Press Dump switch.

Question 17

When will the Safety Valve close/be closed?

Answer 17

Safety Valve is wired through a landing gear safety switch. If either the Cabin Press Dump switch is in PRESS or the Landing Gear Safety Switch is open or the vacuum source or electrical power is lost the Safety Valve will close to atmosphere except at maximum pressure differential of 6.1 psi.

Question 18

Is there any protection against outside air pressure exceeding cabin pressure?

Answer 18

A negative pressure relief diaphragm is incorporated into the Outflow and Safety Valves to prevent outside atmospheric pressure from exceeding cabin pressure during rapid descent.

Question 19

What controls bleed air and mixing of ambient air?

Answer 19

A Flow Control Unit forward of the firewall in each nacelle controls bleed air flow and the mixing of ambient air to make up the total air flow to the cabin for pressurization, heating, and ventilation.

Question 20

Is the Flow Control Unit pneumatic or electric?

Answer 20

The Flow Control Unit is fully pneumatic except for an integral electric solenoid fire wall shutoff valve controlled by the BLEED AIR VALVE switches on the overhead control panel.

Question 21

Is the ambient air solenoid operated by the landing gear safety switch normally open or closed?

Answer 21

A normally open NO solenoid operated by the landing gear safety switch controls the introduction of ambient air flow to the cabin on take off.
Through a time delay, input of ambient air flow introduction is first through the left flow control unit, then 4 seconds later air flow through the right control unit.

Question 22

How is the Bleed Air Firewall Shutoff Valve held open?

Answer 22

Bleed Air Firewall Shutoff Valve in the Flow Control Unit is a spring loaded, bellows operated valve that is held open by bleed air pressure. When the solenoid is shut off or when bleed air diminishes on engine shutdown the Firewall Valve CLOSES.

Question 23

Is the environmental shutoff valve solenoid normally open or closed?

Answer 23

Environmental shutoff valve solenoid is normally closed. When a switch is positioned to either OFF or ENVR OFF the corresponding environmental shutoff valve is closed and no bleed air can pass through the flow control unit or enter the cabin.

Question 24

What happens with a bleed air switch in the OPEN position?

Answer 24

When a BLEED AIR VALVE switch is in the OPEN position the corresponding solenoid valve is electrically held open, opening the environmental shutoff valve, the air mixture can then flow through the valve and into the cabin.