Air Systems Flashcards
What are the sources of air to the Bleed Air System?
- Engines
- APU
- External Pneumatic/conditioned Air
Cart.
What is the purpose of the Air Supply Controller (ASC)?
The ASC digitally controls the output of the 4th and 10th stage pneumatic air in response to bleed air demands
*Eng. Bleed air is controlled electronically by IASC (Integrated Air Supply Controller)
**It has two subsystems Air Supply Controller ASC for bleed regulation and Pack Flow/Temp Controller for pack output temp and flow control.
**NG ENGINE BLEED OPERATION:
Engine bleed air is extracted from the 5th and 9th stages of the compressor section
What causes the engine bleed air valve to automatically close?
High Temperature (254 C) or High Pressure (170 psi) for 5 seconds.
*ASC closes both PRSOV’s in response to the above conditions
(Pressure Regulating Shutoff Valves)
What does the illumination of the BLEED (amber) light indicate?
Bleed sensors closed the engine bleed valve due to excessively high:
1. engine bleed air temp.
2. bleed pressure
3. a failure within the
Bleed Air System that’s
not resettable, or
4. an incorrect bleed air
config is detected after
takeoff or go-around
What will cause the automatic closure of the APU Bleed Valve?
Shutting down the APU.
The valve closes automatically when the APU is shut down, regardless of BLEED switch position.
Selecting OFF closes the valve too
What is the position of the isolation valve with the ISOLATION VALVE switch in AUTO?
Auto, with both engine bleeds ON and both packs in AUTO or HIGH = the isolation valve is closed.
(each engine supplies one pack)
Manually selecting any eng. BLEED or PACK to OFF will automatically open isolation valve
Memory aide - ISO valve is closed if all the corner switches are on, which is normal.
*it opens automatically if any pack or engine bleed switch is put to OFF
What does the illumination of the DUAL BLEED (amber) light indicate?
It indicates that two sources of bleed air (Engine and APU) could be
pressurizing the left bleed duct.
This exposes the APU to
engine bleed back-pressure should the APU check valve fail.
Configurations that cause this are:
*Engine No. 1 (left bleed) switch ON and APU bleed air valve open, and/or
*Engine No. 2 (right bleed) switch ON, ISOLATION VALVE OPEN, and APU bleed air valve open
*The DUAL BLEED light monitors engine BLEED switch position and APU bleed valve position.
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?
Maximum Certified Ceiling
A single pack in high can maintain press and temp up to 41,000’
What causes a pack to automatically switch to high airflow?
Normal clean config:
Airborne, flaps up,
both PACK switches AUTO, ENG Bleed switches to ON:
If one pack fails or a pack switch is selected to OFF, the remaining pack automatically switches to high air flow to increase ventilation.
*this function is inhibited on the ground or with flaps extended to preserve engine power for single engine ops
**Also, the ill. of EQUIP SMOKE light on the equipment cooling system will automatically switch both packs to high to prevent smoke entering cabin
How many controllers does each PACK have?
2 integrated pack/zone electronic controllers.
Each controller has a digital primary, and an analog backup control for the opposite side pack.
What does the illumination of the PACK (amber) light indicate?
Enlarge Image
Do the Flight Attendants have any control of cabin temperature?
Yes. Flight attendants may adjust the forward and aft cabin zones +/- 3 degrees Celsius.
How is the failure of either the primary or standby PACK controller indicated on the ground?
- Illumination of the MAINT (amber) light along with the Master Caution and OVERHEAD annunciation after landing indicates the failure of an associated zone control.
What provides cooling air for the PACK systems?
Ram Air System provides cooling air for the Air Conditioning Pack Heat Exchangers. Operation is controlled through the positioning of the Ram Air Inlet Doors. They move to the full-open position for maximum cooling:
o on the ground, or
o during slow flight with flaps extended.
How is a supply duct overheat indicated?
Illumination of the ZONE TEMP (amber) light or a failure of both left and right IASC
(Integrated Air System
Controller)
An overheat may be reset using the TRIP RESET if the supply duct as cooled
What is the primary source of conditioned air for the flight deck?
Air for the Flight Deck is directly from the left pack
What is the purpose of the recirculation fans?
Reduces bleed air load on the engines, resulting in more efficient operation.
Approximately 50% of the air is recirculated.
Provides a higher relative humidity in the cabin (engine bleed air is very dry).
Reduction of particulates and micro-organisms due to high air recirculation rates through the HEPA filter.
Can pre-conditioned air temperature be controlled by the PACKs?
No!
(pack switches should be OFF)
What does the EQUIP COOLING OFF light indicate?
NORM fan has failed. Select ALTN fan, this should restore airflow and extinguish the OFF light in about 5 minutes
Loss of airflow due to the failure of the respective Equipment Cooling Fan
Normal and alt fans are powered from different elec. busses. Loss of air flow due to normal fan failure is indicated by the OFF light and an OVERHEAD, and MASTER CAUTION lights. Selecting the alternate fan should restore airflow and extinguish the OFF light after about 5 min.
What does the illumination of the EQUIP SMOKE light indicate?
Two smoke detectors are installed downstream of the fans.
If smoke is detected, EQUIP SMOKE, with the OVERHEAD annunciation and the Master Caution light.
When smoke’s detected system automatically sets the PACKS to High, turns off the E&E fans for 5 minutes, and opens the overboard exhaust valve to the smoke position.
After 5 minutes the E&E fans resume operation. If smoke is re-detected, the cycle repeats.
How is the alternate pressurization controller selected?
Automatically in the event of a controller fault, or if selected by the pilot.
The system changes the active controller for each flight
Selecting ALTN on the Cabin pressurization panel will switch controller to standby controller
How are pressurization controller failures indicated?
Ill’ of amber AUTO FAIL caution light with green ALTN light means failure of normal press. system and the alternate system has taken over. Once the switch is selected to ALTN, then the amber
AUTO FAIL light extinguishes and the green ALTN light remains, indicating single-channel operation.
Dual cabin pressurization controller failure would illuminate the AUTO FAIL light but not the ALTN light. In this situation, the FLT ALT and LAND ALT windows will display dashes.
Ill’ of the AUTO FAIL (amber) light with:
-loss of DC power
or
-outflow valve control fault
or
-cabin press controller fault
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
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)
What would cause the OFF SCHED DESCENT light to illuminate?
The aircraft has not reached the altitude selected on the Pressurization Control panel before beginning a descent.
OFF SCHED DESCENT, along with AIR COND system annunciator and MASTER CAUTION lights
The CABIN ALTITUDE light and altitude warning horn activate at approximately what altitude?
10,000 feet +/- 1,000 feet.
Can the cabin altitude warning horn be silenced using the ALT HORN CUTOUT switch above 10,000 feet?
Yes. Pushing the ALT HORN CUTOUT switch will silence the horn, but the CABIN ALTITUDE lights will remain ill’ until the condition is fixed
What does a Wing Body Overheat light mean?
View Image
When is APU high airflow mode available?
*question not in back of Air Systems chapter
*aircraft is on the ground,
*both engine BLEED switches are OFF,
*APU is operating,
*APU BLEED switch ON, and
*either or both PACK switches are
positioned to HIGH
