ATR 42/72-600 Systems Guide — Chapter I: Fire Protection
Chapter I. FIRE PROTECTION (FCOM DSC 26)¶
1. POWER PLANT FIRE DETECTION SCHEMATIC (Page 103)¶
The engine fire protection architecture utilizes a closed, continuous gas-expansion loop topology (Lindberg type) configured around the exterior compressor casing, accessory gearbox, and turbine modules of Engine 1 and Engine 2.
ENGINE LOOP INTERCONNECTION LAW
┌────────────────────────────────────────────────────────┐
│ ENGINE CORE BOUNDARY MONITORING MATRIX │
│ │
│ ┌──────────────┐ ┌──────────────┐ │
│ │ LOOP A DET │ │ LOOP B DET │ │
│ └──────┬───────┘ └──────┬───────┘ │
│ │ │ │
│ └───────────────┬────────────────┘ │
│ ▼ │
│ [ CENTRAL CORE AND LOGIC ] │
│ [ (Requires Dual Capture) ] │
└───────────────────────────┬────────────────────────────┘
▼
┌────────────────────────────────────────────────────────┐
│ FLIGHT WARNING SYSTEM │
│ ──► Active CRC Alarm ──► Master Warning Flashing │
│ ──► Red EWD Alarm Line ──► Fire Handle Illuminated Red│
└────────────────────────────────────────────────────────┘
2. DUAL-LOOP FIRE SENSING LOGIC PARAMETERS (Page 104)¶
To eliminate false alarms caused by localized duct damage or short circuits, each engine fire detection network relies on parallel-routed channels: Loop A and Loop B.
2.1. Systemic Verification Rules¶
- Normal Fire Condition: Requires a simultaneous pressure or thermal expansion spike across both Loop A and Loop B. This satisfies the validation gates and triggers the full Master Warning system.
- Single Channel Failure: If an operational check identifies a short circuit or structural line break on Loop A, the crew isolates that channel. The internal logic shifts entirely to a single-channel configuration, allowing Loop B alone to trigger the fire warning if a thermal surge occurs.
- Core Sensor Discrepancies: If a massive thermal surge occurs on one loop while the secondary loop registers normal baseline values, the system suppresses the master warning red line and outputs a localized loop fault advisory message on the display instead.
3. COMPARTMENT SMOKE AND CARGO MONITORING LAWS (Page 105)¶
The structural forward cargo bay, aft cargo bay, and lavatory enclosures are monitored continuously by dual-channel optical smoke detectors.
- Optical Sensing Mechanics: The detectors sample ambient air drawn through internal light-labyrinth chambers. If airborne smoke particulates accumulate beyond calibrated density targets, they scatter internal infrared beams onto photoelectric receiver nodes, completing the alert circuit.
- Ventilation Coordination: When a cargo smoke sensor generates an alert, the system automatically commands the respective compartment intake and exhaust ventilation valves to close. This seals the compartment to starve the fire of oxygen.
4. CENTRAL FIRE PROTECTION OVERALL SCHEMATIC (Page 106)¶
This schematic tracks the routing paths of the automated fire extinguishing lines from the storage bottles to the engine nacelles and cargo spaces.
- Engine Fire Extinguisher Bottles: Each engine nacelle is backed up by two independent fire extinguishing cylinders (Bottle 1 and Bottle 2) cross-plumbed across a common manifold. This design allows both bottles to be discharged into a single engine core if a fire persists.
- Cargo Extinguisher Network: Employs a dual-bottle configuration consisting of a high-rate discharge bottle (for rapid knock-down of open flame) and a metered slow-discharge bottle (which bleeds suppressant gas into the sealed cargo space over 45-60 minutes to prevent re-ignition during an emergency diversion).
5. ENGINE FIRE HANDLE PANEL CONTROL LOGIC (Page 107)¶
Located prominently on the center overhead console framework.
ENGINE FIRE CONTROL PANEL
┌────────────────────────────────────────────────────────┐
│ ENG FIRE │
│ │
│ [ ENG 1 FIRE ] [ ENG 2 FIRE ] │
│ (HANDLE 1) (HANDLE 2) │
│ │
│ SQUIB EXTGH 1 SQUIB EXTGH 2 │
│ [ARMED] [ DISCH ] [ARMED] [ DISCH ] │
│ │
└────────────────────────────────────────────────────────┘
5.1. Pulling the Engine Fire Handle: The Five Structural Closures¶
Pulling an Engine Fire Handle mechanically releases its locking latch and executes five critical system isolations to starve and contain the engine fire:
- Fuel System Isolation: Commands the low-pressure (LP) fuel shutoff valve inside the wing root to close, cutting off all fuel flow to the affected engine.
- Pneumatic Bleed Air Isolation: Closes the main Engine Bleed Valve and associated High-Pressure (HP) Valve to isolate the pneumatic manifold.
- Environmental Control Isolation: Closes the respective Pack Flow Control Valve to prevent toxic smoke from entering the cabin mixing chamber.
- Electrical Generation Isolation: Opens the line contactors for both the DC Starter-Generator and ACW Generator, stripping the failed engine's power sources off the main grids.
- Extinguisher Squib Arming: Electrically arms the explosive squib firing heads on both fire bottles, illuminating the amber ARMED indicators on the fire panel.
5.2. Extinguisher Discharge Actions¶
Turning the pulled Fire Handle left or right fires the high-pressure squib pins, discharging Halon gas directly into the engine nacelle core. Successful pressure discharge changes the panel state text from ARMED to white DISCH indicators.
6. COMPARTMENT SMOKE OVERHEAD PANEL LAYOUT (Page 108)¶
Located on the center overhead panel space. Controls suppression for cargo and lavatory spaces.
COMPARTMENT SMOKE PANEL
┌────────────────────────────────────────────────────────┐
│ COMPT SMOKE │
│ │
│ FWD CRG AFT CRG LAV │
│ [ SMOKE ] [ SMOKE ] [ SMOKE ] │
│ │
│ AGENT AGENT EXTING │
│ [ DISCH ] [ DISCH ] [ DISCH ] │
└────────────────────────────────────────────────────────┘
- SMOKE Indicator (Red): Illuminates if duplicate optical sensors confirm a smoke density spike inside that zone. This warning activates the continuous repetitive chime (CRC).
- AGENT / EXTING Pushbuttons: Guarded switches used to fire cargo fire extinguishing systems. Pressing the button discharges the fire suppressant gas and illuminates the white DISCH confirmation text once line pressure sensors confirm the bottle is empty.