AIR SYSTEMS

Question 1

What are the sources of air the Bleed Air System?

Answer 1

Bleed air can be supplied by the engines, Auxiliary Power Unit (APU), or an external pneumatic/conditioned air source (on the ground).

Question 2

What is the purpose of the Air Supply Controller (ASC)?

Answer 2

Control of the PRSOV and the HPSOV is achieved by the ASC.

The ASC digitally controls the output of 4th- and 10th-stage pneumatic air in response to bleed air demands.

Duct pressure is maintained by the ASC using the PRSOV.

Question 3

What causes the engine bleed air valve to automatically close?

Answer 3

The IASC will automatically trip both the Pressure Regulating Shutoff Valve (PRSOV) and High Pressure Shutoff Valve (HPSOV) closed in response to high temperature (254°C) or overpressure (170 psi for 5 seconds).

Question 4

What does the illumination of the BLEED light indicate?

Answer 4

• bleed sensor(s) have closed the associated engine bleed air valve for over-temperature or excessive pressurization of the bleed duct, or

• a failure within the Bleed Air System that may not be resettable, or

• an incorrect bleed configuration after takeoff or go-around.

Question 5

What causes the automatic closure of the APU bleed valve?

Answer 5

The valve will automatically close when the APU is shut down, regardless of switch position. Selecting OFF will close the valve.

Question 6

What is the position of the isolation valve with the ISOLATION VALVE switch in AUTO?

Answer 6

In AUTO, the isolation valve is controlled by engine BLEED and PACK control switches. With both engine BLEED switches ON and both PACK switches in AUTO or HIGH, the isolation valve is closed; manually placing any engine BLEED or PACK switch to the OFF position will automatically open the isolation valve.

Question 7

What does the illumination of the DUAL BLEED light indicate?

Answer 7

The DUAL BLEED light illuminates when two sources of bleed air (Engine and APU) could be pressurizing the left bleed duct.

• Engine No. 1 (left bleed) switch ON and APU bleed air valve open

• Engine No. 2 (right bleed) switch ON, ISOLATION VALVE OPEN, and APU bleed air valve open

NOTE: The DUAL BLEED light monitors engine BLEED switch position and APU bleed valve position.

Question 8

In the event of a single pack failure at altitude, the remaining pack is capable of maintaining cabin pressure and comfort up to what altitude?

Answer 8

A single pack in high airflow mode can maintain pressurization and acceptable temperatures up to the maximum certified ceiling.

Question 9

What causes a pack to automatically switch to high airflow?

Answer 9

The AUTO position also has an automatic high airflow mode. If a pack or an engine fails when the aircraft is airborne with Flaps UP and both engine BLEED switches ON, the operating pack will automatically switch to high airflow mode. Additionally, positioning a PACK switch OFF in flight with the Flaps UP will also cause the remaining pack to go into high airflow mode.

The illumination of the EQUIP SMOKE light of the Equipment Cooling System will automatically switch both packs to high airflow mode to protect against smoke entering the cabin.

Question 10

How many controllers does each pack have?

Answer 10

Both air conditioning packs have a dual channel pack/zone electronic controller. Each controller has a digital primary channel to control its respective pack and an analog channel that provides backup control for the opposite side pack.

Question 11

What does the illumination of the PACK light indicate?

Answer 11

The PACK light on the BLEED air panel illuminates to indicate:

• failure of both the primary and standby pack controls for the same pack; the pack will continue to operate uncontrolled unless tripped off by excessive temperature, or
• failure of the pack valve to open when commanded, or
• an incorrect PACK switch configuration after takeoff, (both PACK switches OFF for 45 sec. after flaps UP)
• a pack overheat

Question 12

Do the Flight Attendants have any control of cabin temperature?

Answer 12

Temperature set points for the forward and aft passenger cabin zones can be adjusted +/- 3 degrees from the Flight Attendant panel in the cabin.

Question 13

How is the failure of either the primary or standby pack controller indicated on the ground?

Answer 13

The MAINT light and the OVERHEAD System Annunciator and MASTER CAUTION lights will illuminate after landing to indicate failure of the associated zone control.

Question 14

What provides cooling air for the pack systems?

Answer 14

The Ram Air System provides cooling air for the air conditioning pack heat exchangers.

Question 15

How is a supply duct overheat indicated?

Answer 15

ZONE TEMP lights indicate a supply duct overheat of the associated temperature zone.

Question 16

What is the primary source of conditioned air for the Flight Deck?

Answer 16

The Flight Deck receives air directly from the left pack.

Question 17

What is the purpose of the recirculation fans?

Answer 17

Recirculated air through use of two recirculation fans reduces the Engine Bleed Air and Pack System demands and increases engine efficiency. Roughly 50% of cabin air is recirculated air, which also helps to maintain humidity in the cabin from the very low humidity air from the engine bleeds. Airborne particulates and micro-organisms are filtered through High Efficiency Particulate (HEPA) filters, delivering clean air back to the cabin.

Question 18

Can pre-conditioned air temperature be controlled by the packs?

Answer 18

NO, Conditioned air temperature is controlled at the external air source.

Question 19

What does the Equipment Cooling System cool?

Answer 19

The Equipment Cooling System cools the electronic equipment in the Flight Deck and Electrical Equipment Bay (E & E Bay).

Question 20

Which cargo compartment is heated by warm air from the Equipment Cooling System’s exhaust fans?

Answer 20

In flight with high cabin pressure differentials, the Overboard Exhaust Valve is normally closed and diffuses warm air to the lining of the forward cargo compartment.

Question 21

What does the EQUIP COOLING OFF light indicate?

Answer 21

Loss of airflow due to the failure of a fan is indicated by the illumination of the OFF light.

Question 22

What does the illumination of the EQUIP SMOKE light indicate?

Answer 22

Two smoke detectors are installed downstream of the fans. The EQUIP SMOKE light and the OVERHEAD System Annunciator and MASTER CAUTION lights will illuminate if smoke is detected.

Question 23

How is the alternate pressurization controller selected?

Answer 23

When the pressurization mode selector is in the AUTO position, the Pressurization Control System operates automatically using one of the two automatic controllers. The system changes the active controller with each flight. Selecting ALTN on the Cabin Pressurization panel will switch control to the standby controller.

Question 24

How are pressurization controller failures indicated?

Answer 24

The AUTO FAIL light on the Cabin Pressurization panel will illuminate if:
• loss of DC power occurs, or
• outflow valve control fault, or
• cabin pressurization controller fault (Dual controller Failure FLT ALT and LAND ALT window dashes)

If the cabin pressurization controller is not responding properly, the following will also illuminate the AUTO FAIL light:
• Excessive differential pressure (> 8.75 psi)
• Excessive rate of cabin pressure change (± 2000 fpm)
• High cabin altitude (> 15,800 ft)

Question 25

What would cause the OFF SCHED DESCENT light to illuminate?

Answer 25

Should a descent begin prior to the aircraft reaching the set FLT ALT, e.g., an air turn-back during climb, the OFF SCHED DESCENT light will illuminate.

Question 26

The CABIN ALTITUDE light and altitude warning horn activate at approximately what altitude?

Answer 26

If the cabin altitude exceeds 10,000 ± 1000 ft, the CABIN ALTITIDE lights illuminate and the cabin altitude warning horn (intermittent) activates.

Question 27

Can the cabin altitude warning horn be silenced using the ALT HORN CUTOUT switch about 10,000 ft?

Answer 27

An ALT HORN CUTOUT switch is located on the Cabin Altitude panel. Pushing the ALT HORN CUTOUT switch will silence the intermittent horn, but the CABIN ALTITUDE lights will remain illuminated until the high cabin altitude condition no longer exists.