2. Air Systems Flashcards
WING-BODY OVERHEAT Light
- Not resettable,
- Indicates overheat from bleed air duct leak,
- Monitors Engine Struts, Inboard Wing Leading Edges, Air Conditioning Bays,
- For L side also, Keel Beam or APU Bleed Air Duct
BLEED TRIP OFF Light
Indicates excessive Engine Bleed Air Temperature or Pressure
TRIP RESET Switch
Resets:
- BLEED TRIP OFF,
- PACK,
- ZONE TEMP lights
Related Bleed Air Valve / Pack Valve / Trim Air Modulating Valve opens
ZONE TEMP Lights
CONT CAB:
- Indicates duct overheat or failure of the both flight deck temperature controls,
- During RECALL indicates failure of primary or standby flight deck temperature contol
- Extinguishes when Master Caution is reset
FWD / AFT CAB:
- Indicates duct overheat,
- During RECALL indicates failure of the associated zone temperature control
- Extinguishes when Master Caution is reset
PACK Switches
AUTO:
- With both Packs operating, each Pack regulates to low flow,
- With one Pack operating, it regulates to high flow in flight with Flaps UP,
- When operating one Pack from APU (both BLEED switches OFF) regulates to high flow
HIGH:
- Provides maximum flow rate on the ground with APU BLEED ON
RECIRC FAN Switches
AUTO inflight:
- L operates if both Packs operating unless either PACK Switch is in HIGH,
- R operates if both Packs operating unless both PACK Switch is in HIGH,
AUTO on the ground:
- L operates unless both PACK Switch is in HIGH
- R operates even if both PACK Switch is in HIGH
PACK Light
- Indicates Pack Trip Off or failure of both primary and standby Pack Controls,
- During RECALL indicates failure of either primary or standby Pack Control,
- Extinguishes when Master Caution is reset
Systems Relying on Bleed Air
- Air conditioning/pressurization,
- Thermal Anti-icing,
- Engine Starting,
- Hydraulic reservoir pressurization,
- Water tank pressurization,
- Nitrogen Generation System
Engine Bleed System Supply
- Obtained from 5th and 9th stages of compressor section,
- When 5th stage low pressure is insufficient high stage valve modulates open
Engine and APU Bleed Air Valves
- Engines valves are Pressure Regulator and Shut-off Valves (PRSOV),
- All valves DC activated and pressure operated
Duct Pressure Transmitters
- Indicator is AC operated,
- As long as there is sufficient air for cabin pressurization, differences between L/R considered normal
Isolation Valve
- AC operated,
- AUTO: If any Engine Bleed or Pack Switch is OFF, valve is open. Otherwise it’s closed
Airconditioning Distribution
- Left PACK: Flows directly to Flight Deck, excess air flows to Mix Manifold,
- Right PACK: Flows directly to Mix Manifold,
- Recirculation System: Flows directly to Mix Manifold,
- Preconditioned Ground Air: Flows directly to Mix Manifold
PACK Air Sources
- APU is capable to supply 2 Packs on the ground and single Pack in flight,
- Do not operate more than one Pack from one Engine,
- Most External Air Carts are capable of supplying both Packs
Single Pack Operation
In High Flow, capable of maintaining pressurization and acceptable temperatures up to maximum certified ceiling
Automatic PACK High Flow Switch
For Engine Bleeds:
- Inflight with Flaps UP,
- Both PACK switches AUTO,
- Both Engine Bleed switches ON,
- If one Pack fails or selected OFF
For APU Bleed:
- When both Engine Bleed switches are OFF,
- Both PACK switches AUTO,
- Switches to High Flow regardless of air/gnd or Flap position,
- If one Pack fails
Ram Air System
- Provides cooling air for heat exchangers,
- Automatically controlled by Packs,
- On the ground or during slow flight with Flaps extended doors are full open,
- In normal cruise modulates between open and closed,
- Deflector doors extend electrically by air-ground safety sensor
- They prevent slush ingestion prior liftoff and after touchdown
Cooling Cycle
- Bleed Air passing through a heat exchanger for cooling,
- Then air flows to an air cycle machine for refrigeration,
- Processed cold air combined with hot air which bypassed air cycle machine,
- Mixed air passes through a high pressure water seperator which removes moisture
Pack Temperature Controls
- Electronic controllers command the Pack Temperature Control Valve toward open or closed,
- If primary Pack Control fails, the affected Pack is controlled by the Standby Pack Control in the opposite Controller,
- If both Controls fails for the same Pack, Pack will continue to operate until excessive temperatures cause a Pack to trip off
Zone Temperature Selector Range
18-30 degrees
Zone Temperature Control Basics
- Packs produce an air temperature that satisfies the zone which requires the most cooling,
- Zone temperature is controlled by introducing the proper amount of trim air to the zone ducts,
- Quantity of trim air is regulated by individual trim air modulating valves
Single Pack Operation and Trim Air
- If TRIM AIR switch is ON, it’s same as during 2 Packs operation,
- If TRIM AIR switch is OFF, Pack attempts to produce an air temperature to satisfy the average temperature demands of all 3 zones
Zone Temperature Control Modes
- Left Electronic Controller controls Aft Cabin Zone and provides backup for Flight Deck,
- Right Electronic Controller controls the FWD Cabin Zone and provides primary control for Flight Deck
FWD or AFT Cabin Temperature Control Failure
- Associated Trim Air Modulating Valve closes,
- Temperature Selectors operate normally but 2 cabin zone selections will be averaged
Unbalanced Pack Temperature Control Mode
- Any failure affecting supply of Trim Air will cause the Temperature Control System to control both Packs independently,
- If Flight Deck Trim Air is lost: L Pack provides the selected temperature to Flight Deck and R Pack will satisfy the Cabin Zone which requires most cooling,
- If a Cabin Zone or all Trim Air is lost: FWD and AFT temperature demands averaged for control of R Pack
Standby Pack Average Temperature
- When all Zone Controls and Primary Pack Controls fail,
- Standby Pack Controls command the Packs:
- To produce air temperatures for an average temperature demand of 2 Cabin Zones,
- Trim Air Modulating Valves close,
- Flight Deck Temperature Selector has no affect on the Standby Pack Controls
Fixed Cabin Temperature
- If all Temperature Selectors OFF,
- L Pack maintains 24 degrees,
- R Pack maintains 18 degrees,
- Measured at the Pack Temperature Sensor
Passenger Cabin Air Distribution
- Sidewall Risers and,
- Overhead Distribution Duct
Recirculation Fans
- Driven by AC motors,
- Reduces Pack Load and Engine Bleed Air demand,
- Air from Cabin and Electrical Equipment Compartment drawn to FWD Cargo Hold,
- There it is filtered and recirculated to the Mix Manifold
Equipment Cooling
- Consists of Supply and Exhaust ducts,
- Each duct has a normal and an alternate Fan
Exhaust duct collects warm air from:
- Flight Deck Displays,
- Overhead and Aft Electronic Panels,
- CB Panels,
- E&E compartment
Equipment Cooling Alternate Fan Selection
Should restore airflow and extinguish OFF light within 5s
Equipment Overtemperature On The Ground
Call horn heard in the Nose Wheel Well
FWD Cargo Smoke Penetration Prevention
- When RECIRC FAN switches OFF and PACK switches HIGH,
- Smoke Control Relay will shut off Equipment Cooling Supply Fan for 5 minutes,
- Smoke Control Relay will inhibit the EQUIPMENT COOLING OFF light for 5 minutes,
- After 5 minutes fans and light will return to normal operation,
- Equipment Cooling Exhaust Fan will be shut off for the remainder of the flight,
- If any RECIRC FAN or PACK switches moved out of these positions, Cooling Fans begin to operate again
FWD Cargo Heating
- Recirculation Fan System circulates air from cabin and E/E Cooling System into the FWD Cargo,
- As Overboard Exhaust Valve closes to increase differential pressure, exhaust from E/E Cooling is also diffused into the FWD Cargo
Pressurization Controlled By
2 identical Automatic Controllers (AUTO or ALTN) and a Manual Mode (MAN) regulating:
- Mainly by Outflow valve and,
- Overboard Exhaust Valve
Pressure Relief Valves
- 2 valves limiting differential pressure to a maximum 9.1psi,
- 1 negative relief valve prevents external pressure from exceeding internal pressure
Cabin Pressure Controller Motor Types
All uses DC motor
Cabin Pressure Controller Inputs
- Throttle position from SMYD computers,
- Air/Ground sensors,
Also from ADIRU:
- Static Pressure,
- Baro Corrected Altitude (from CPT and F/Os EFIS),
- Non-corrected Altitude,
- CAS,
Overboard Exhaust Valve Operation
- On the ground and in flight with low differential pressure, it is open,
- In flight at higher cabin differential pressures, it is normally closed,
- Will open when either Pack switch is in HIGH and R RECIRC FAN OFF
Pressurization Auto Mode Operation
- Consist 2 identical controllers which alternately sequenced as a primary for each flight,
- On the ground at lower power settings, cabin is depressurized by opening Outflow Valve to full open,
- The cabin begins to pressurize at higher power settings on the ground,
- This slight pressurization make transition more gradual for humans and gives better response to ground effect pressure change,
- In the air increases altitude at a rate proportional to the airplane climb rate
Auto Mode Cruise/Descent Mode Activation
- Cruise: When airplane climbs within 0.25psi of the selected FLT ALT,
- Descent: When airplane descends 0.25psi below the selected FLT ALT
Differential Pressure Limits
- Above 37000FT: 8.35psid,
- 28000-37000FT: 7.80psid,
- At or below 28000: 7.45psid
AUTOFAIL Illumination Reasons
- Loss of DC power,
- Controller Fault,
- Outflow Control Fault,
- Excessive differential pressure (> 8.75psid),
- Excessive rate of cabin pressure change (+/- 2000FPM),
- High cabin altitude (> 15800FT)
Pressurization MAN Mode
- Uses a seperate DC motor, powered by DC Standby system,
- Drives outflow valve at a faster rate than AUTO and ALTN modes,
- Full range motion takes 20s
