737 Air Systems Flashcards
What sources supply air to the bleed air (pneumatic) system?
Engines, APU, or an external pneumatic air cart/source (on the ground)
What systems rely on bleed (pneumatic) air for operation?
Air Conditioning/Pressurization Wing Thermal Anti-Icing Engine Thermal Anti-Icing (respective engine bleed air) Engine Starting Hydraulic Reservoir Pressurization Water Tank Pressurization Nitrogen Generation
What is the purpose of the Engine Bleed Air Valve, and how is it operated?
Acts as a pressure regulator and shutoff valve.
Operates with Engine Bleed Air Switch (ON and OFF - electrically activated, pneumatically actuated)
ON = opens the respective Bleed Air Valve.
Automatically closes when fire handle pulled & during engine start (isolate and ventilate)
What is the purpose of the Precooler System?
Regulates temperature of bleed air using fan duct air across an air to air heat exchanger. To COOL THE PACKS
What causes Bleed Trip Sensors to automatically close the Engine Bleed Air Valve?
Overheat or overpressure.
Associated with a Master Caution and AIR COND annunciator.
How is the bleed trip condition reset?
Push the TRIP RESET switch (Condition must no longer exist for a successful reset).
What do the WING-BODY OVERHEAT, BLEED TRIP OFF, and DUAL BLEED amber lights on the Bleed Air Panel indicate?
WING-BODY OVERHEAT = leak in a critical area air duct (no reset possible)
BLEED TRIP OFF = overheat or overpressure (TRIP RESET possible)
DUAL BLEED = indicates APU bleed valve is open and
· engine #1 bleed switch is on, and/or
· engine #2 bleed switch is on and isolation valve is open
What causes these lights to illuminate?
WING-BODY OVERHEAT
BLEED TRIP OFF
DUAL BLEED
WING-BODY OVERHEAT = an overheat from a bleed air duct, leak in the engine pylon, inboard wing leading edge, left air conditioning bay, keel beam or APU bleed air duct.
BLEED TRIP OFF = excessive engine bleed air temp (254) or over pressure (220 psi)
DUAL BLEED = APU bleed valve is open and
· engine #1 bleed switch is on, or
· engine #2 bleed switch is on and isolation valve is open
What is the purpose of the APU Bleed Air Valve, and how is it operated?
To provide bleed air to the left duct.
Opens with APU Bleed Air switch ON and APU operating above 95%.
Closes automatically when APU shuts down, or with back pressure (APU and engine bleed air valves open).
SH 2.010 pg 7
What is the purpose of the Isolation Valve?
The Isolation Valve isolates the left and right bleed air ducts during normal operations, when in the closed position.
What do the Isolation Valve positions CLOSE, OPEN, and AUTO do?
CLOSE = forces valve closed, isolating L & R bleed air ducts
OPEN = forces valve open, allowing flow between L & R
AUTO = valve will be closed when
· Both engine bleed are switched are ON and
· Both Air Conditioning PACK switched are in AUTO or HIGH
How do the Engine BLEED Air or Air Conditioning PACK switches impact operation of the Isolation Valve?
Both switches will open the isolation valve in AUTO.
*Isolation valve position is not affected by the APU BLEED AIR Switch
Where is the external pneumatic air connection located?
Located on the right side of the aircraft (immediately aft of the right landing light) underneath a quick release access panel
What is the path of conditioned air from an external (ground) source?
Pre-conditioned ground air enters directly into the mixing manifold downstream of the packs.
When connected to external air, which position should the PACK switches be in?
OFF
What is the primary source of conditioned air to the Flight Deck? To the passenger cabin?
- Flight Deck = Left pack
- Pax Cabin = Right pack through mix manifold
How is the forward cargo compartment heated?
Exhaust air from the equipment cooling fans
How is the aft cargo compartment heated?
Aft cargo is not heated
What do the PACK amber lights on the Bleed Air Panel indicate? What causes these lights to illuminate?
- PACK (with MC/AIR COND) = overheat condition OR fault of both primary and secondary controllers. A pack trip will cause the pack valve to close. (TRIP RESET possible)
- PACK (on recall only) = failure of primary OR standby controller
What happens with the Master Caution light during a failure of Primary pack control? Standby pack control?
Nothing - single failure is only shown in recall
Both fail? MASTER CAUTION and AIR COND annunciator
A single pack in high flow mode can maintain pressurization and comfort up to what altitude?
41000 feet
Explain the auto logic for high airflow during normal operations and with a pack or engine failure.
Normal operations - automatically in HIGH with engine bleed air switches OFF and APU bleed air switch ON
In flight with flaps up: Pack failure - other pack automatically in HIGH Engine failure (N2 less than 50%) - other side pack automatically in HIGH
What controls pack temperature control?
Zone that needs the most cooling is what decides what the packs do, then the Trim Air System regulates the other 2 zones
What is the purpose of the recirculation fans?
Reduces demand on the bleed air system and recirculates air.
RIGHT recirc fan takes air from holes in floor and runs it to mix manifold
LEFT recirc fan takes in air from the air conditioning distribution compartment
What is the purpose of the Equipment Cooling System?
Cools electronic equipment in the Flight Deck and the E/E bay.
Smoke removal (drives to full open and allows smoke to escape)
Heats FWD cargo compartment (keeps the puppies warm)
What does the EQUIP COOLING OFF (amber) light indicate?
loss of airflow due to the failure of the respective Equipment Cooling Fan.
(Checklist will lead you to use alternate fan)
What causes the AUTO FAIL and OFF SCHED DESCENT amber lights to illuminate?
AUTO FAIL
Loss of DC power
Controller or outflow valve fault
Excessive pressure differential or rate change or high cabin altitude
OFF SCHED DESCENT
Aircraft begins to descend without having reached the preset cruise altitude. always set lower altitude before descending will extinguish if you return to altitude or set lower altitude
How does the primary heat exchanger lower the bleed air temperature?
Ram air lowers the bleed air temperature. Insufficient ram air flow is augmented with an induction impeller driven by an extension of the air cycle machine (ACM) shaft.
What is indicated by a bright blue RAM DOOR FULL OPEN light? Dim blue? Extinguished?
RAM DOOR FULL OPEN = Ram door full open
Dim blue = never
Extinguished = closed or modulating
What do the ALTN (green) light and MANUAL (green) light on the Cabin Pressurization panel indicate?
ALTN - Alternate pressurization mode is on and active
MANUAL - manual pressurization mode, selected by mode switch
What causes these lights to illuminate? ALTN (green) and MANUAL (green)
ALTN - manually selected or main CPC unit has failed (AUTO FAIL is illuminated)
MANUAL - mode selected to manual pressurization
What does the Pressurization Mode Selector do?
Selects Cabin Pressure Controller operational mode
Describe the 3 temperature control zones.
CONT CAB - flight deck
FWD CAB - forward cabin
AFT CAB - aft cabin
What does an illuminated ZONE TEMP (amber) light indicate?
ZONE TEMP = Duct overheat, (trim air valve for that area automatically closes) OR controller failure
What happens with the Master Caution light when ZONE TEMP illuminates?
Master caution (AIR COND) illuminates.
What is the purpose of the Mix Manifold?
Mixes recirculated air with conditioned air from PACKs
On the Cabin Pressurization Panel, what do the FLT ALT indicator and LAND ALT indicator display?
FLT ALT - scheduled cruise altitude
LAND ALT - altitude of intended landing field
*What are indications and impact of a panel failure?
Display 8888888 or all dashes
8888888 = panel is still operating
———– = panel is no longer operating
What is indicated by the CABIN ALTITUDE (red) light and the Cabin Altitude Warning Horn? How can this horn be silenced?
CABIN ALTITUDE = cabin altitude exceeds 10,000ft +/- 1000
Silenced with ALT HORN CUTOUT switch, located on the overhead panel
DUAL BLEED light comes on
Apu bleed valve open AND:
Engine 1 bleed air switch on OR
Engine 2 bleed air switch on and iso valve open
What causes pressurization mode to change to ALTN?
1 loss of dc power
2 controller fault
3 outflow valve controller fault
4 excessive differential pressure over 8.75 psi
5 Excessive rate of cabin pressure change greater than 2000 ft./min.
6 high cabin alt above 15800 feet
