7 - environmental control

Question 1

What stage of the engine to the packs get air from?

Answer 1

The 10th stage

Question 2

Where are the air conditioning units located

Answer 2

In the aft equipment bay

Question 3

Where is the air distributed that comes from the left and right pack?

Answer 3

The left pack will normally supply the cockpit and the right pack will supply the cabin

Question 4

What regulates the pressure of the air from the tenth stage before it enters the pack?

Answer 4

Due to extreme pressure of the Air from the 10th stage, the air could damage the pack if the pressure was not reduced. This is the job of the pack pressure regulating shut off valve “PRSOV” and his used to reduce the pressure of the air before it enters the pack.

Question 5

What would occur if the PRSOV failed

Answer 5

The valve would Close, the pack would shut down and a pack high-pressure EICAS message would be displayed.

Question 6

How does the PRSOV help a single pack supply sufficient pressure to the flight deck in the cabin during single pack operations?

Answer 6

There are two pressure settings, one for dual pack and one for single pack. When two packs are available, the PRSOVs reduce the 10th stage pressure to a normal pressure. During single pack operations the single PRSOV Will increase the operating pressure, which will permit the single pack to supply the cabin and flight deck with sufficient airflow. It will not be at the same volume as with both packs operating.

Question 7

What is the single pack operating altitude limit?

Answer 7

25,000 feet

Question 8

What cools the hot air for the air-conditioning system?

Answer 8

An air cycle machine and heat exchangers coolS THE hot compressed air.

Question 9

What is the purpose of the ram air scoop at the base of the vertical stabilizer?

Answer 9

Air enters this scoop and is used as the cooling means for the air to air in heat exchangers. The ram air flows across the pre-cooler and dual heat exchangers thus cooling the pack air. The cooling ram air exits through the events located at the lower right and left sides of the fuselage in the aft area. When the aircraft is on the ground there is no ram air to enter the scoop so I fan that is driven by the air cycle machine draws the air in the scoop.

Question 10

What are the sources of air conditioning bleed air?

Answer 10

APU
Engines
External air cart

Question 11

What is the altitude limit for extracting bleed air from the APU for air conditioning? What will happen if the APU is used for bleed air above this altitude?

Answer 11

The limit is 15,000 feet. If this altitude is exceeded the EICAS caution message APU BLEED AIR ON Will appear.

Question 12

Where is the left pack air distributed?

Answer 12

The air will be sent to the flight deck gaspers, vents and side console outlets. It will also be used for EICAS and EFIS Display cooling.

Question 13

Where is the right pack air distributed?

Answer 13

It is distributed to the floor outlets in the passenger cabin, laboratory, galley, and the gaspers on the PSU’s

Question 14

Where is the cabin air exhausted?

Answer 14

The air is sent under the floor to outflow valves on the aft pressure bulkhead.

Question 15

Where is the low pressure ground air connection?

Answer 15

It Is located behind the wing on the right side of the aircraft.

Question 16

Does the low pressure air cart supply air to the PACks for the aircraft cooling?

Answer 16

No, the air is sent directly to the distribution manifold, which then travels to all the outlets

Question 17

What must be done before the low pressure air can be turned on?

Answer 17

The main cabin door or avionics bay door must be open.

Question 18

Explain how suitable airflow is maintained in the cargo bay.

Answer 18

A fan draws recirculated passenger cabin exhaust air from under the floor into the cargo bay to maintain suitable airflow and temperature.

In addition to the recirculated air, there’s an optional automatic temperature control that uses right fresh pack air for cooling and an electric heater for increasing temperature. This controller maintains a the cargo bay that is better suited for live animals.

Question 19

What happens to the cargo SOVs if the cargo smoke detectors detect smoke?

Answer 19

The SOVs used for circulation of air will automatically close. If COND AIR Is selected, the SOV from right pack for air conditioned air will close and the heater turned off

Question 20

What happens when fan is selected on the cargo fan switch?

Answer 20

A fan is energized in the cargo recirculation and exhaust shut off valves are open. Air is then taken from the passenger cabin exhaust duct and used to supply suitable airflow to the cargo bay.

Question 21

Is over heat protection provided in the cargo bay?

Answer 21

Over the protection is provided only with the condition air option selected.

Question 22

What does an amber CARGO OVHT on the EICAS indicate?

Answer 22

The EICAS message will only occur if the conditioned air option is installed. If the cargo bay temperature reaches 35°C and conditioned air is selected, and overheat condition is detected. The heater is deenergized and the EICAS CARGO OVHT is presented. The CARGO COND AIR switch should be selected to FAN.

Question 23

How is cabin pressurization maintained?

Answer 23

By two outflow valves controlling the rate in the air leaves the vessel.

Question 24

What happens to the cargo air when one or both of the cargo smoke detectors detect smoke?

Answer 24

The cargo intake and exhaust SOVs Close, the cargo fan shuts down, the condition air valve closes and the heater shuts down.

Question 25

Briefly explain how the outflow valves operate.

Answer 25

There are two outflow valves located on the aft bulkhead that control the amount of air leaving the aircraft. Vacuum pressure from a jet pump driven by the 10th stage bleed air manifold is used to open the outflow valves which are held close to by springs.

Question 26

What indicates which CPC is active?

Answer 26

It is identified on the ECS page.

Question 27

When will the active CPC become the standby CPC?

Answer 27

The active CPC can be changed anytime manually by pressing the PRESS CONTROL switch light on the CABIN PRESS Control panel two times. The active also become the standby three minutes after landing. The standby will return to the active upon the next landing.

Question 28

What are the automatic modes of the CPC’s?

Answer 28

Ground mode
Pre-pressurization mode
Take off abort mode
Climb mode 
Flight abort Mode 
Cruise mode
Descent mode
Landing mode

Question 29

Explain the ground mode of the CPC

Answer 29

After AC power is applied the CTC completes a self test. The ground mode will start at the completion of the self test and the safety valves will be driven full open to provide ventilation on the ground. 10th stage bleed air is needed for the valves to be driven open

Question 30

Explain the pre-pressurization mode of the CPC

Answer 30

This mode is activated when the thrust levers are set for take off. The outflow valves start to Close and the cabin will be pressurized to approximately 150 feet below field elevation the pre pressurization of the aircraft eliminates any noticeable pressure bumps

Question 31

Explain the take off abort mode of the CPC

Answer 31

When the thrust levers are retarded during a rejected take off the CPC will bring the cabin back to field elevation at 500 ft./m or 20 seconds and then drive the outflow Vals full open. The CPC will then be in the ground mode

Question 32

Explain the climb mode of the CPC

Answer 32

The CPC controls cabin pressurization based on the selected landing field elevation and a theoretical schedule of cabin altitude versus aircraft altitude. The profile that the cabin climbs on is based on the aircraft rate of climb, which that profile is about 300 to 500 ft./m

Question 33

Explain the flight abort mode of the CPC

Answer 33

This mode is armed within the first 10 minutes of the flight and the aircraft is still below 6000 feet. The purpose of this mode is so the pilot does not have to reset the landing elevation when returning to the departure field. The mode is activated with a decent of 1000 ft./m or more.

Question 34

Explain the cruise mode of the CPC

Answer 34

There is than assigned cabin altitude for every cruising altitude. Once in cruise mode the descent mode is armed automatically.

Question 35

Explain the decent mode of the CPC

Answer 35

The cabin Will descend based on the rate of descent in-flight time remaining. Flight time remaining is based on information received from the ADCs. The cabin will normally descend at 300 ft./m feet per minute until the cabin altitude is 150 feet below selected landing field elevation.

Question 36

Explain the landing mode of the CPC

Answer 36

When the PSEU senses weight on wheels and the thrust levers are at idle the CPC will transfer from the decent mode to landing mode. In the landing mode CPC will climb the cabin at 500 ft./m for 60 seconds and then enter the ground mode. Three minutes after landing the active CPC will become the standby.

Question 37

Are any electrical controls involved in manual pressurization?

Answer 37

None

Question 38

What does the red FAULT in the PRESS CONT switch light indicate?

Answer 38

The light indicates that both CPCs have failed.

Question 39

How are the EFIS and EICAS cathode ray tubes (CRTs) cooled?

Answer 39

The CRTs are cooled by air-conditioned pack air distributed by fans.

Question 40

Explain the avionics exhaust fan

Answer 40

That operates when the AC buses are powered. It extracts the exhaust air from the CRTs the ARINC Racks, the pedestal panel and the avionics bay.

When the passenger door or the service door is open the exhaust air is discharged through the overboard exhaust valve. If this valve fails open when the doors are closed, and Amber OVBD COOL will be displayed on the EICAS.

Wendy passenger and service stores are closed, the overboard exhaust valve closes. The inboard exhaust valve opens to send the air into the fuselage. A white EICAS INBD COOL FAIL Will indicate failure of this valve.

Question 41

Will there be any warning if there is a low airflow for avionics cooling?

Answer 41

There will be an EICAS caution message of DISPLAY COOL if there is a duct blockage or fan failure by the low flow detectors.

Question 42

What does the amber FAIL light in the left or right pack switch light indicate?

Answer 42

Pack has shut down due to overpressure or over temperature.

Question 43

At what pack temperature does the amber EICAS message L PACK HI TEMP appear?

Answer 43

When the pack temperature reaches 85°C

Question 44

What’s supplies cooling air for the heat exchangers?

Answer 44

The ram air scoop at the base of the vertical stabilizer is where cooling air enters.

Question 45

What is the source of the vacuum for the outflow valves?

Answer 45

a jet pump and 10th stage bleed air

Question 46

When would you use ram air ventilation?

Answer 46

When both packs have failed In flight ram air ventilation would be used

Question 47

When will the cabin altitude aural warning be heard?

Answer 47

When cabin altitude is above 10,000 feet.