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Which areas on an aircraft are typically protected by a fixed fire detection and extinguishing system?
Which areas on an aircraft are typically protected by a fixed fire detection and extinguishing system?
What is the purpose of a fixed fire protection system in an aircraft?
What is the purpose of a fixed fire protection system in an aircraft?
What type of detector is NOT mentioned as part of the aircraft fire protection systems?
What type of detector is NOT mentioned as part of the aircraft fire protection systems?
Which class of fire involves ordinary combustible materials like wood and paper?
Which class of fire involves ordinary combustible materials like wood and paper?
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Which class of fire requires extinguishing media that is electrically nonconductive?
Which class of fire requires extinguishing media that is electrically nonconductive?
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Which of the following is an example of Class D fires?
Which of the following is an example of Class D fires?
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What does the term 'fixed' refer to in the context of aircraft fire protection systems?
What does the term 'fixed' refer to in the context of aircraft fire protection systems?
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Which of the following is NOT a typical zone protected by fixed fire systems?
Which of the following is NOT a typical zone protected by fixed fire systems?
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What is a primary requirement for an ideal fire detection system in aircraft?
What is a primary requirement for an ideal fire detection system in aircraft?
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Which type of fire detection system is known for being heat-sensitive and completing electrical circuits at a certain temperature?
Which type of fire detection system is known for being heat-sensitive and completing electrical circuits at a certain temperature?
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What feature of an ideal fire detection system indicates that a fire has re-ignited?
What feature of an ideal fire detection system indicates that a fire has re-ignited?
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Which component allows for electrically testing the detector system from the aircraft cockpit?
Which component allows for electrically testing the detector system from the aircraft cockpit?
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What principle does an ionization smoke detector use to detect smoke?
What principle does an ionization smoke detector use to detect smoke?
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What is one of the uses of thermal switches in fire detection systems?
What is one of the uses of thermal switches in fire detection systems?
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What happens to the electrical current flow in an ionization smoke detector when smoke is present?
What happens to the electrical current flow in an ionization smoke detector when smoke is present?
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Which components are part of an optical smoke detector system?
Which components are part of an optical smoke detector system?
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Which is NOT an ideal characteristic of a fire detection system mentioned?
Which is NOT an ideal characteristic of a fire detection system mentioned?
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What type of fire detection system is typically installed in areas with higher fire risks?
What type of fire detection system is typically installed in areas with higher fire risks?
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What occurs in an optical smoke detector when smoke particles are present?
What occurs in an optical smoke detector when smoke particles are present?
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What is a key feature of a thermal switch system in fire detection?
What is a key feature of a thermal switch system in fire detection?
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What does the intensity monitor photodiode in an optical smoke detector do?
What does the intensity monitor photodiode in an optical smoke detector do?
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What indication does a lavatory smoke detector provide during an alert?
What indication does a lavatory smoke detector provide during an alert?
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How does the optical smoke detector identify contamination or defective diodes?
How does the optical smoke detector identify contamination or defective diodes?
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What is the purpose of smoke detection systems in fire protection?
What is the purpose of smoke detection systems in fire protection?
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What happens to the color of the chemical when carbon monoxide is present?
What happens to the color of the chemical when carbon monoxide is present?
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What is a key advantage of Halon as a fire extinguishing agent in aviation?
What is a key advantage of Halon as a fire extinguishing agent in aviation?
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Which of the following best describes carbon dioxide's method of extinguishing fires?
Which of the following best describes carbon dioxide's method of extinguishing fires?
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Where are fixed fire extinguishing systems installed in transport aircraft?
Where are fixed fire extinguishing systems installed in transport aircraft?
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What indication occurs in the cockpit when there is smoke in a cargo compartment?
What indication occurs in the cockpit when there is smoke in a cargo compartment?
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Why is Halon considered a clean agent?
Why is Halon considered a clean agent?
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What happens to the smoke detector in a cargo compartment when smoke is detected?
What happens to the smoke detector in a cargo compartment when smoke is detected?
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Which statement is true regarding Halon 1211?
Which statement is true regarding Halon 1211?
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What activates the cargo compartment extinguisher system?
What activates the cargo compartment extinguisher system?
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What is the primary function of the dump system in the cargo compartment extinguisher system?
What is the primary function of the dump system in the cargo compartment extinguisher system?
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How long can the metered system keep the fire extinguished?
How long can the metered system keep the fire extinguished?
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What role does the squib play in the extinguishing system?
What role does the squib play in the extinguishing system?
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What happens when the cargo discharge switch is activated?
What happens when the cargo discharge switch is activated?
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What unique feature is present in the extinguishing bottles of the cargo compartment system?
What unique feature is present in the extinguishing bottles of the cargo compartment system?
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What type of fire extinguisher is used in the lavatory compartment?
What type of fire extinguisher is used in the lavatory compartment?
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What is one indication that a bottle has been discharged in the cargo compartment?
What is one indication that a bottle has been discharged in the cargo compartment?
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What triggers the discharge of Halon from the fire extinguisher bottle?
What triggers the discharge of Halon from the fire extinguisher bottle?
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Which issue is NOT addressed in the maintenance of a fire detection system?
Which issue is NOT addressed in the maintenance of a fire detection system?
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What should be done if dents or kinks are found in the sensing elements?
What should be done if dents or kinks are found in the sensing elements?
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What specific part of the sensing elements should be inspected for tightness during maintenance?
What specific part of the sensing elements should be inspected for tightness during maintenance?
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What is the consequence of not adhering to the manufacturer's specifications during maintenance?
What is the consequence of not adhering to the manufacturer's specifications during maintenance?
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In high activity areas around aircraft engines, what increases the likelihood of damage to sensing elements?
In high activity areas around aircraft engines, what increases the likelihood of damage to sensing elements?
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What visual inspection is included in an inspection program for continuous-loop systems?
What visual inspection is included in an inspection program for continuous-loop systems?
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Which specific maintenance task involves ensuring the safety and tightness of a component in a fire detection system?
Which specific maintenance task involves ensuring the safety and tightness of a component in a fire detection system?
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Study Notes
ME3531 Aircraft Systems - Chapter 5: Fire Protection Systems
- Fires are a major threat to aircraft, and modern aircraft have fixed fire protection systems.
- "Fixed" systems are permanently installed, unlike portable extinguishers. A modern fire protection system includes both fire detection and fire extinguishing.
- Typical areas protected include engines, auxiliary power units (APUs), cargo/baggage, lavatories, electronic bays, wheel wells, and bleed air ducts.
- Fire protection systems utilize various detection methods.
Fire Detection Methods
- Rate-of-temperature-rise detectors
- Overheat detectors
- Smoke detectors
- Carbon monoxide detectors
- Visual observation by crew/passengers
Classes of Fires
- Class A: Ordinary combustible materials (wood, cloth, paper, rubber, plastics).
- Class B: Flammable liquids (petroleum oils, greases, tars, oil-based paints).
- Class C: Energized electrical equipment (requires electrically nonconductive extinguishing media).
- Class D: Combustible metals (magnesium, titanium, zirconium, sodium, lithium, potassium).
Requirements for Overheat and Fire Protection Systems
- Ideal fire detection systems avoid false alarms under any condition.
- Systems quickly identify and locate the fire and its exact location.
- They clearly indicate if the fire is out or re-ignited.
- Continuous indication during the fire.
- Detecting system testing from the cockpit.
- Light weight and adaptable mounting.
- Resisting damage from exposure to extreme conditions.
- Minimal electrical consumption when not detecting a fire.
- Cockpit indicators (visual and audible) pinpointing the fire location.
- A separate detector system for each engine is often implemented.
Fire Detection/Overheat Systems: Thermal Switch Systems
- Thermal switches are heat-sensitive and complete electrical circuits at a designated temperature.
- These are connected in parallel, but in series with indicator lights.
- Thermal switch will close to trigger a fire or overheat alarm if one section of the system exceeds the set temperature.
Fire Detection/Overheat Systems: Thermocouple Systems
- Thermocouples are constructed from dissimilar metals (chromel and constantan) and measure temperature differential arising from a hot junction (where metals meet and are exposed to heat) compared to a reference junction.
- Thermocouples detect the rate of temperature rise, useful for faster-developing fires.
- This system differs from thermal switches by its temperature detection by rate and not just temperature.
- When a fire occurs, the hot junction heats faster than the reference junction causing a warning signal for the crew.
Fire Detection/Overheat Systems: Continuous-Loop Systems
- Continuous-loop systems provide more extensive coverage than spot detectors.
- This system is frequently used in powerplants and wheel well areas.
- Two common types include thermistor-based systems (e.g., Kidde and Fenwal) and pneumatic-based systems (e.g., Systron-Donner).
Fire Detection/Overheat Systems: Pneumatic Continuous-Loop Systems
- Pneumatic detectors have two components: overall average temperature and discrete temperature increases.
- These detectors use helium gas, whose pressure changes with the environmental temperature, which triggers an alarm.
- Pressure diaphragm within the system is the sole moving part and operates the electrical alarm circuit.
- Typical temperature settings range from 200°F (93°C) to 850°F (454°C).
Fire Detection/Overheat Systems: Discrete Function
- Specific areas of the tube can reach a predetermined temperature.
- Detection by temperature output causes hydrogen gas release and an alarm.
- Averaging and discrete functions are reversible. This gas returns to the core when the area cools.
- A pressure warning device shows operational status or alerts flight crew if the system's functionality is not working properly.
Smoke Detection Systems: Light Refraction Type
- Detects changes and amount of light refracted by smoke particles via a photoelectric device.
- Smoke particles reduce transmitted light, activating an electrical signal, and setting off an alarm.
Smoke Detection Systems: Ionization Type
- Uses radioactive material to ionize oxygen and nitrogen molecules in the sampled air, creating a current.
- Smoke particles attach to these ions and reduce the current, triggering an alarm.
Smoke Detection Systems: Optical Type
- Optical detectors monitor light generated in the smoke detector chamber.
- These are placed between light emitting diodes (LEDs) and scattered light detectors.
- Smoke particles cause more light to scatter and are detected by the monitoring device, triggering an alarm.
Lavatory Smoke Detectors
- Each lavatory has a smoke detector in the ceiling.
- A warning light or alarm system activates in the cockpit when the sensor detects smoke and fire.
- A fire extinguisher is also fitted to these lavatories.
Flame Detection Systems
- Optical sensors detect specific hydrocarbon flame radiation (infrared or ultraviolet).
- The sensed radiation changes the device temperature and triggers an output.
- This system is differentiated from other devices by its use of a filter to block non-target radiation emissions.
Carbon Monoxide Detection System
- Carbon monoxide detectors are used to detect carbon monoxide, a byproduct of incomplete combustion. Its presence in high concentrations poses a significant risk to health.
- Two common detection systems include electronic and chemical color-change detectors.
- A chemical color-change detector's color changes from tan to gray when CO is present; an electronic device produces an alarm triggered by the chemical.
- Replaceable chemical indicators allow for continued functionality.
Extinguishing Agents: Halogenated Hydrocarbons
- Halon is an effective fire extinguishing agent for aircraft environments.
- It is electrically non-conducting, leaves minimal residue, and is relatively non-toxic.
- Halon 1301a is used for total flooding, and Halon 1211 for streaming applications.
Extinguishing Agents: Inert Cold Gases
- Carbon dioxide (CO2) is an effective extinguishing agent, also commonly used in aircraft.
- It dilutes the oxygen content, interrupting combustion.
Installed Aircraft Fire Extinguisher Systems
- Aircraft have various fire suppression systems, most commonly installed in turbine engines, APUs, cargo/baggage, and lavatories.
Cargo Compartment Fire Detection and Extinguisher System
- Smoke detection systems are strategically placed in the cargo compartment. If smoke is detected, warnings are given in the cockpit.
- An aural and visual warning system is used to alert crew when smoke is detected.
Cargo Compartment Extinguisher System
- Systems are designed for fast activation.
- A "dump" discharge activates immediately upon activation.
- A metered system slowly dispenses the extinguishing agent over time. The system is designed to maintain the proper concentration of extinguishing agent for 180 minutes or longer.
Lavatory Fire Extinguisher System
- Lavatories contain a fire extinguisher that discharges when a preset temperature is reached in the lavatory.
- Pressurized Halon or a similar extinguishing agent is used, and when the specified temperature threshold (170°F/77°C) is reached, it triggers the system's activation.
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Description
Explore the crucial fire protection systems in modern aircraft as covered in ME3531. This chapter delves into various detection methods and the different classes of fires that may occur on an aircraft, emphasizing the significance of fixed fire protection systems. Learn how these systems contribute to ensuring flight safety.
