ATR 42/72-600 Systems Guide — Chapter D: Air
Chapter D. AIR (FCOM DSC 21, 36)¶
1. PNEUMATIC SYSTEM OVERVIEW (Page 36)¶
The Pneumatic System (ATA 36) taps high-pressure bleed air from the engine compressors to supply secondary systems across the airframe.
Supplied Sub-systems:¶
- Air Conditioning and Passenger Cabin Environmental Packs (ATA 21).
- Cabin Pressurization Control System (ATA 21).
- De-Icing Boots for Wing, Tail, and Engine Nacelle Leading Edges (ATA 30).
- Hydraulic Reservoir Head-Pressure Pressurization.
1.1. Bleed Air Extraction Sources (Page 37)¶
Bleed air is tapped independently from Engine 1 and Engine 2 at two separate compressor stages to optimize temperature and pressure output:
- Intermediate Pressure (IP) Stage: Tapped during mid-to-high power settings (e.g., Takeoff, Climb, Cruise). This is the preferred operational source to conserve engine efficiency.
- High Pressure (HP) Stage: Tapped during low engine power settings (e.g., Flight Idle, Descent). The HP valve opens automatically to compensate for low IP manifold pressure.
1.2. Pneumatic Manifold Schematic Architecture (Page 38)¶
ENGINE 1 MANIFOLD ENGINE 2 MANIFOLD
┌───────────────────────┐ ┌───────────────────────┐
│ [HP Stage] [IP Stage]│ │ [IP Stage] [HP Stage]│
└────┬───────────┬──────┘ └──────┬───────────┬────┘
│ │ │ │
[HP VLV] │ │ [HP VLV]
└─────┬─────┘ └─────┬─────┘
▼ ▼
[ENG 1 BLEED VLV] [ENG 2 BLEED VLV]
│ │
├───────────────► [PACK 1] ├───────────────► [PACK 2]
│ │
▼ ▼
[WING DE-ICE LEAK] [WING DE-ICE LEAK]
│ │
└───────────────► [ CROSS-BLEED VALVE ] ◄───┘
[X-BLEED]
Regulation Values:¶
- Manifold Delivery Pressure: Regulated down to approximately $45\text{ psi}$ by the Bleed Valves.
- Temperature Limits: Pre-coolers utilize fan bypass air to drop extraction air temperatures below a max structural safety envelope of $274^\circ\text{C}$.
2. AIR BLEED OVERHEAD PANEL LAYOUT (Page 39)¶
Located on the center overhead panel assembly. Controls the distribution and extraction pathways for both engine bleed sources.
AIR BLEED CONTROL PANEL
┌────────────────────────────────────────────────────────┐
│ AIR BLEED │
│ │
│ HP VALVE 1 ENG 1 BLEED ENG 2 BLEED HP VALVE 2 │
│ [ FAULT ] [ OFF ] [ OFF ] [ FAULT ] │
│ [FAULT ] [FAULT ] │
│ │
│ X BLEED │
│ [ AUTO ] │
│ [OFF] [ON ] │
└────────────────────────────────────────────────────────┐
2.1. Component Functional Matrix¶
| Switch Control | Type | Normal Setting | Functional Operation / System Logic |
|---|---|---|---|
| HP VALVE 1 / 2 | Pushbutton | Released (ON) | Automatically schedules the HP bleed valve to open when IP stage pressure drops below system requirements. When depressed (OFF), the HP valve is forced closed. |
| ENG 1 / 2 BLEED | Pushbutton | Released (ON) | Actuates the main bleed control valve. Automatically regulates pneumatic manifold pressure. When depressed (OFF), the valve closes manually. |
| X BLEED | Rotary Selector | AUTO | OFF: Forces the cross-bleed valve closed, isolating the left and right pneumatic networks. |
AUTO: Cross-bleed opens and closes automatically based on single-engine operation or pack fault tracking rules.
ON: Mechanically commands the cross-bleed valve to open, unifying the manifolds. |
3. AIR BLEED FAULT MONITORING PARAMETERS (Page 40)¶
The annunciators built into each button monitor separate thermal and structural breakdown conditions:
3.1. Annunciator Light States and Triggers¶
- BLEED Pushbutton [FAULT] (Amber): Illuminates if any of the following parameters are detected:
- Duct Over-temperature (OVHT): Bleed air temperature downstream of the pre-cooler exceeds $274^\circ\text{C}$. The main bleed valve trips closed automatically.
- Duct Over-pressure: Manifold delivery pressure exceeds limits ($>80\text{ psi}$).
-
Hardware Mismatch: Physical position of the bleed valve does not match the commanded state of the button.
-
BLEED Pushbutton [OFF] (White): Illuminates continuously when the pushbutton is manually depressed, confirming the bleed valve is closed.
- HP VALVE Pushbutton [FAULT] (Amber): Illuminates if the high-pressure bleed extraction valve fails to reach its commanded position, or if an over-pressure spike is localized inside the upstream HP supply line.
3.2. Bleed Leak Detection System Logic (Page 41)¶
The pneumatic ducts are continuously monitored by structural loop detection lines (sensing elements) to identify insulation breakdowns or high-temperature escapes along the structural frames.
- Monitored Zones: Left Wing Duct, Right Wing Duct, Feed Ducts to Air Conditioning Packs, and the Fuselage Cross-Bleed Matrix.
- System Response: If a pneumatic leak triggers the threshold sensor:
- The associated MC/MW system initializes.
- An explicit warning line flashes on the EWD indicating the affected zone (e.g.,
PROP DE-ICE LOOPorAIR BLEED LEAK). - The respective automated controls command the main bleed valves to trip shut to prevent thermal damage to peripheral structural ribs.
3.3. Ground Pneumatic Operation (Page 42)¶
When the aircraft is operating on the ground without engine bleed supply active, an external high-pressure Ground Cart air source can be linked directly to the pneumatic distribution manifold via the dedicated ground connector coupling point.
- Manifold Cross-Feed Setup: To ensure conditioned air reaches both distribution networks during ground cart operations, the cockpit X BLEED rotary switch selection must be set to the mechanical ON position, cross-feeding the single external input across both the Left and Right Pack valves.
2. AIR CONDITIONING SYSTEM (ATA 21) (Page 43)¶
The air conditioning system conditions high-pressure bleed air down to comfortable cabin temperature ranges and maintains active volume exchanges across the sealed structural zones.
AIR CONDITIONING COMPONENT FLOW PATH
┌────────────────────────────────────────────────────────┐
│ BLEED MANIFOLD SOURCE │
└───────────────────────────┬────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────┐
│ PACK FLOW CONTROL VALVE │
│ (Modulates Volume Inflow Rates) │
└───────────────────────────┬────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────┐
│ AIR CYCLE MACHINE (ACM) │
│ (Heat Exchangers, Compressor, and Turbine) │
└───────────────────────────┬────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────┐
│ MIXING CHAMBER │
│ (Unifies Clean Conditioned Streams) │
└───────────────────────────┬────────────────────────────┘
│
┌──────────────┴──────────────┐
▼ ▼
┌────────────────────────┐ ┌────────────────────────┐
│ FLIGHT DECK ZONE │ │ PASSENGER CABIN ZONE │
└────────────────────────┘ └────────────────────────┘
2.1. Environmental Pack Air Cycle Mechanics (Page 44)¶
- Primary Cooling Phase: Raw bleed air passes through the primary stage air-to-air heat exchanger, using external ram air scoops to lower initial temperatures.
- Compression Phase: The pre-cooled air travels through the centrifugal compressor section of the Air Cycle Machine (ACM), raising pressure lines to optimize temperature extraction parameters.
- Secondary Cooling Phase: Air crosses the secondary stage heat exchanger for an additional ram-air cooling drop.
- Expansion Phase: Air expands rapidly across the turbine wheel assembly. Energy extraction drops the physical temperature down near freezing levels before the flow transitions out toward the main water separators.
2.1. AIR CONDITIONING SCHEMATIC DIAGRAM (Page 45)¶
The internal distribution ducts coordinate the mix of fresh pack air with treated internal recirculation loops to sustain constant airflow velocity metrics.
- Pack Output Balance: - Pack 1 is optimized to dump its primary thermal conditioned path into the Flight Deck distribution ductwork.
-
Pack 2 is optimized to dump its primary path into the main Passenger Cabin ceiling distribution track.
-
Recirculation Fans Integration: To minimize total bleed air demands on the power plants, the RECIRC system uses electric fan assemblies to draw ambient cabin air from the floor grittiness profiles, filter the volume, and mix it directly inside the central mixing chamber manifold.
2.2. COMPT TEMP CONTROL PANEL LAYOUT (Page 46)¶
Located on the center overhead panel space. Controls zone temp scheduling profiles.
COMPT TEMP OVERHEAD PANEL
┌────────────────────────────────────────────────────────┐
│ COMPT TEMP │
│ │
│ FLT DECK CABIN │
│ [ MAN ] [ MAN ] │
│ ( O ) ( O ) │
│ COOL WARM COOL WARM │
│ │
│ PACK VALVE RE-SET │
│ [ PB ] │
└────────────────────────────────────────────────────────┐
Component Functional Logic:¶
- FLT DECK / CABIN Selectors: Continuous rotary rheostats used to manually dial in target temperature boundaries.
- MAN Annunciators (Amber): Illuminate continuously when manual temp control selection override modes are enabled via the rotary baseline select gates.
- PACK VALVE RE-SET Pushbutton: Acts as the master manual reset pathway to clear electronic trip latches on the pack valves after an over-temperature condition cooling sequence satisfies system safety profiles.
2.3. Temperature Regulation Electronics (Page 47)¶
The system operates across two selectable control modes:
- Automatic Mode (AUTO): Digital temperature controllers sample data from duct temperature bulbs, cockpit skin sensors, and selector values. The digital loops drive individual electric trim air valves to inject hot bypass air into the cold pack lines, holding the selected temperature constant.
- Manual Mode (MAN): Bypasses the digital processing loops. Cockpit commands drive the trim air control valves directly via hardwired electrical line signals, requiring flight crews to monitor duct temperature behavior visually on the display screens.
2.4. Pack Over-Temperature (OVHT) Protections (Page 48)¶
To prevent internal fire hazards or component warping within the composite structural ducts, the systems guide tracks strict thermal limit controls:
- Trigger Limits: If the compressor discharge temperature within the Air Cycle Machine breaches a calibrated max boundary ($>204^\circ\text{C}$), or if duct supply feeds overheat:
- The internal logic tracks an automatic emergency safety shutdown.
- The associated flow control pack valve shuts immediately.
- The overhead panel illuminates the PACK FAULT amber alert alongside the OVHT warning text string.
2.5. Flight Deck and Passenger Cabin Balancing Logic (Page 49)¶
- Cross-Zone Fallback: If Pack 1 is manually deactivated or suffers an internal thermal lockout, the mixer valve architecture opens common paths. Pack 2 automatically handles the processing workload for both the Flight Deck and the Passenger Cabin zones.
- Note: Total volume delivery rates scale down during single-pack operations to protect engine torque performance reserves during high-altitude operations.
3. AVIONICS VENTILATION SYSTEM (ATA 21) (Page 50)¶
The Avionics Ventilation system directs constant cooling airflow streams across the forward flight deck electronics racks, instrument display modules, and under-floor CRT/IMA processing blocks to prevent electrical system failures from thermal overload.
AVIONICS VENT OVERHEAD PANEL
┌────────────────────────────────────────────────────────┐
│ AVIONICS VENT │
│ │
│ EXHAUST EXTRACT │
│ [ OVHT ] [ OVHT ] │
│ [ FAULT ] [ FAULT ] │
│ │
└────────────────────────────────────────────────────────┘
3.1. Annunciator Light Diagnostics and Warning Loops:¶
- EXHAUST Pushbutton [FAULT] (Amber): Illuminates if airflow parameters within the main overhead structural exhaust duct drop below calibrated output thresholds, or if the electric exhaust fan motor fails.
- EXHAUST Pushbutton [OVHT] (Amber): Illuminates if the temperature of the air stream exiting the avionics rack structures breaches a safety max limit ($>45^\circ\text{C}$).
- EXTRACT Pushbutton [FAULT] (Amber): Indicates an internal electrical loop breakdown or physical failure of the main under-floor extraction fan assembly.
- EXTRACT Pushbutton [OVHT] (Amber): Alerts the crew that the internal electronics bay internal skin temperature bounds are approaching operational limits, requiring manual backup configuration adjustments.
4.2. Pressurization System Architecture & Control Laws (Page 51)¶
The Pressurization Control System maintains a safe cabin environment using dual automatic digital channels and a completely independent manual pneumatic backup loop.
- Outflow Valve (OFV) Assembly: A single structural unit located on the aft pressure bulkhead containing two separate sub-valves:
- An electro-pneumatic valve driven by the digital automatic system.
-
A purely pneumatic valve driven by manual flight deck selections.
-
Cabin Pressure Controllers (CPC 1 & CPC 2): Two identical digital channels that share computing overhead via an active-standby configuration. Channel rotation occurs automatically after every landing cycle.
- Control System Inputs: The active digital controller samples parameters directly from the Flight Management System (FMS), Air Data Computers (ADC), and internal skin pressure transducers.
4.3. Cabin Pressure Display Field & Synoptics (Page 52)¶
Real-time structural pressurization readouts are permanently mapped to the Engine and Warning Display (EWD) and can be checked graphically on the MFD SYSTEMS synoptic page.
EWD PRESSURIZATION STATUS FIELD
┌────────────────────────────────────────────────────────┐
│ CAB ALT [ 550 ft ] ΔP [ 4.85 psi ] │
│ CAB RATE [ +150 fpm ] LDG ELEV[ 340 ft ] │
└────────────────────────────────────────────────────────┘
Alert Limits and Protective System Logic:¶
- Cabin Altitude Advisory (Cyan): Normal scheduled cabin metrics.
- Cabin Altitude Caution (Amber): Triggers automatically if cabin altitude climbs above $8,500\text{ ft}$.
- Cabin Altitude Warning (Red): Triggers if cabin altitude breaches structural safety boundaries ($>10,000\text{ ft}$). This activates the Continuous Repetitive Chime (CRC), illuminates the Master Warning light, and generates the
CABIN ALTwarning message on the EWD. - Automatic Utility Activation: When a Red
CABIN ALTwarning is active, the system automatically illuminates the passenger cabin overhead signs, overrides normalAUTOselector software, and commands the cabin oxygen masks to drop.
4.4. Pressurization Overhead Control Panel Layout (Page 53)¶
Located on the center overhead console.
PRESSURIZATION OVERHEAD PANEL
┌────────────────────────────────────────────────────────┐
│ PRESSURIZATION │
│ │
│ MODE SEL DUMP │
│ [ MAN ] [ NORM ] │
│ [ FAULT ] [ DUMP ] │
│ │
│ MAN RATE MAN ALT │
│ ( O ) (UP) │
│ MIN MAX [OFF] │
│ (DOWN) │
└────────────────────────────────────────────────────────┘
Component Functional Matrix:¶
| Control Element | Type | Default Setting | Functional / Systemic Operation Logic |
|---|---|---|---|
| MODE SEL | Pushbutton | Released (AUTO) | Fully automated digital cabin scheduling via the active CPC. When depressed (MAN, Amber text), digital software is bypassed, shifting control to the manual pneumatic system. |
| MODE SEL [FAULT] | Annunciator | Extinguished | Illuminates Amber if both digital CPC channels experience a simultaneous processor failure. System requires immediate shift to manual mode. |
| DUMP | Guarded Toggle | NORM | NORM: System schedules pressure parameters normally. |
DUMP: Sends an immediate open command to the outflow valves. Rapidly depressurizes the aircraft cabin down to atmospheric ambient levels or safe safety limits. | | MAN RATE | Potentiometer | Detent Position | Active only in MAN mode. Controls the scheduling speed of the pneumatic reference chamber to determine how fast cabin altitude changes. | | MAN ALT | Spring-loaded Toggle | Center (OFF) | Active only in MAN mode. Directly modulates pneumatic supply lines to the manual outflow valve actuator. Pulling UP drives the valve open (climbs cabin altitude); pushing DOWN closes the valve (lowers cabin altitude). |
4.5. Manual Control Operation & Valve Mechanics (Page 54)¶
When the flight crew manually shifts the system into MAN mode, all electrical current to the primary electro-pneumatic actuator is isolated.
- Pneumatic Loop Drive: The position of the manual outflow valve is driven entirely by metering jet lines controlled by the
MAN ALTtoggle. - Rate Limits: The
MAN RATEknob mechanically restricts the internal pneumatic orifice track to limit extreme pressure changes, preventing structural damage to passenger eardrums during manual recovery profiles.