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ATR 42/72-600 Systems Guide — Chapter N: Ice and Rain Protection

2026-06-23

Chapter N. ICE AND RAIN PROTECTION (FCOM DSC 30)

1. ICE AND RAIN PROTECTION SYSTEM SCHEMATIC (Page 154)

The Ice and Rain Protection framework (ATA 30) coordinates multiple thermal systems to protect the airframe from structural degradation caused by ice accretion.

  ICE AND RAIN DEFENSE SOURCE REPLICAS
  ┌────────────────────────────────────────────────────────┐
  │                     AIRCRAFT MATRICES                  │
  └─────────────┬────────────────────────────┬─────────────┘
                │                            │
                ▼                            ▼
  ┌────────────────────────┐    ┌────────────────────────┐
  │   PNEUMATIC DE-ICING   │    │  ELECTRICAL ANTI-ICING  │
  │ (Pneumatic Boot Arrays)│    │(Resistive Heating Grids)│
  └─────────────┬──────────┘    └────────────┬───────────┘
                │                            │
                ▼                            ▼
     - Wing Leading Edges        - Propeller Blades
     - Tail Stabilizer Edges     - Flight Deck Windshields
     - Engine Nacelle Intakes    - Pitot/Static/TAT Probes

Operational Philosophy Differences

  • De-Icing Systems: Designed to cycle active inflation blocks to break up and shed ice after a layer has physically accumulated on the structural skin sheets.
  • Anti-Icing Systems: Designed to maintain continuous thermal output levels to prevent ice crystals from ever bonding to critical aerodynamic paths or data sensor ports.

2. PROBES, WINDSHIELD HEATING & WIPER SYSTEMS (Page 155)

Flight deck transparency panels and external data monitoring arrays rely on localized electrical heating networks to maintain raw visibility and data line integrity.

2.1. Transparency Panel Systems

  • Windshield Heating Grids: Heavy-duty transparent resistive element layers are bonded inside the forward windshield glass panes. Powered directly by ACW BUS 1 (Left windshield) and ACW BUS 2 (Right windshield).
  • Operating Logic Modes: Controlled via the overhead console switches. The system cycles internal line current continuously to hold panel structures within optimized elastic temperature brackets, preventing windshield cracking and keeping the glass clear of frost.

2.2. Data Probe Protection Matrices

  • Automatic Power Scheduling: Pitot heads, static ports, alpha vanes (AOA), and Total Air Temperature (TAT) probes contain internal electrical heating filaments.
  • Ground-to-Flight Law Transitions: To prevent ground crew burns or probe filament burnout, the system limits power lines to a low-amperage state while the aircraft is on the ground. The moment the landing gear shock struts uncompress at liftoff, the Multi-Function Computers (MFC) switch the power grid to full operational output automatically.

3. AIRCRAFT PERFORMANCE MONITORING (APM) LOGIC LAWS (Page 156)

The Aircraft Performance Monitoring (APM) computer code runs continuous real-time diagnostic checks to identify aerodynamic drag degradation caused by structural ice accretion.

System Diagnostic Flow

  • Drag Vector Interrogation: The APM system constantly cross-checks live true airspeed, engine torque parameters, and pitch attitude metrics against an un-degraded clean-aircraft performance database.
  • Icing Speed Bug Scaling: If severe or hidden ice accretion breaks smooth airflow over the wings, the APM system shifts safety speed boundaries upward. It automatically updates the PFD speed tapes, scaling up minimum stable speeds ($V_{MSTI}$) by 15 to 30 kt depending on configuration choices.

ICING AOA Alarm Alterations

  • Stall Threshold Compression: When the ice warning loop is active, the stall warning computers change their inner calculation rules.
  • Shaker Modification: The Angle-of-Attack (AOA) activation limit for the mechanical stick shaker drops to a lower angular threshold. This causes the cockpit alert shake to fire much earlier in the alpha spectrum, compensating for the degraded lift performance of an iced wing profile.

4. DE-ICING SYSTEM PNEUMATIC DISTRIBUTION SCHEMATIC (Page 157)

The leading edge boot systems use high-pressure pneumatic lines tapped from the engine bleed manifolds to inflate and deflate structural rubber boot arrays.

  DE-ICING PNEUMATIC ROUTING MAP
  ┌────────────────────────────────────────────────────────┐
  │                 HP/IP AIR BLEED MANIFOLD               │
  └───────────────────────────┬────────────────────────────┘
                              │
                              ▼ [Regulated down to 15 psi]
  ┌────────────────────────────────────────────────────────┐
  │                 CYCLIC DISTRIBUTOR VALVES              │
  └─────┬─────────────────────┬─────────────────────┬──────┘
        │                     │                     │
        ▼                     ▼                     ▼
  ┌───────────────┐     ┌───────────────┐     ┌───────────────┐
  │   OUTER WING  │     │   INNER WING  │     │   TAIL BOOTS  │
  │ (Boot Expand) │     │ (Boot Expand) │     │ (Boot Expand) │
  └───────────────┘     └───────────────┘     └───────────────┘

Vacuum Suction Retention

To prevent inflated rubber boots from buffering or distorting the clean wing airfoil profile during non-alert flight paths, the cyclic distributor valves maintain a continuous internal vacuum suction line against the boots when the de-icing system is turned OFF. This keeps the rubber skins pulled tightly down against the leading-edge structural frames.

5. AIRFRAME BLEED FAULT LOOPS & CYCLING SCHEDULER (Page 158)

The structural boots are scheduled sequentially across the airframe by electronic timer units to minimize the total pneumatic demand on the engine bleed manifolds.

Scheduler Timeline Modes

Selected Mode Total Cycle Duration Section Inflation Timing Sequence
FAST CYCLE 60 Seconds Each structural boot zone (Outer Wings, Inner Wings, Stabilizers) receives inflating pressure for exactly 6 seconds sequentially, followed by a 42-second system rest period under vacuum line hold.
SLOW CYCLE 180 Seconds Individual zones receive pressure for 6 seconds sequentially, followed by an extended 162-second rest period to manage light icing accretion accumulation.

System Low Pressure Warnings

  • Trigger Target: If delivery line pressure inside the active manifold drop-lines falls below operational requirements ($< 15\text{ psi}$) during an active inflation phase:
  • The FWS triggers a single chime Master Caution loop.
  • Generates the amber flashing DE-ICE STRCTR PRESS LO message on the EWD screen, identifying a ruptured boot or frozen cycling distributor valve.

6. ANTI-ICING & DE-ICING OVERHEAD PANEL SPECIFICATIONS (Page 159)

Located on the central overhead panel layout, consolidating all ice protection management controls.

  ANTI-ICE / DE-ICE OVERHEAD CONTROL INTERFACE
  ┌────────────────────────────────────────────────────────┐
  │                     ANTI-ICE & DE-ICE                  │
  │                                                        │
  │    PROP 1        PROP 2       WINDSHIELD    SIDE WINDOW│
  │   [ FAULT ]     [ FAULT ]      [ FAULT ]     [ FAULT ] │
  │   [  OFF  ]     [  OFF  ]      [  OFF  ]     [  OFF  ] │
  │                                                        │
  │      AIRFRAME DE-ICE               TAIL DE-ICE         │
  │         [ SLOW ]                     [  ON  ]          │
  │         [ FAST ]                     [FAULT ]          │
  └────────────────────────────────────────────────────────┘

Annunciator Warning Interpretations:

  • PROP Pushbutton [FAULT] (Amber): Illuminates if the internal electronic distributor detects an un-balanced electrical current draw or a heating element break across the propeller blade de-icing arrays.
  • WINDSHIELD Pushbutton [FAULT] (Amber): Alerts the crew that a windshield resistive grid has overheated ($> 60^\circ\text{C}$) or an internal temperature controller has failed. The power relay automatically isolates the grid to protect the windshield.
  • AIRFRAME DE-ICE Selector Button: Selects between the automated SLOW or FAST cyclic pneumatic inflation profiles.