easa part 66 - module 11.08 - fire protection

B1 Mod 11.08.doc Issue No * Page 1

JAR 66 CATEGORY B1

MODULE 11.08 FIRE PROTECTION

CONTENTS

1 FIRE PROTECTION...................................................................... 1-1

1.1 FIRE DETECTION AND WARNING .................................................... 1-1 1.1.1 Thermal Switch Detectors ............................................. 1-1 1.1.2 Continuous Loop (Fire Wire) Detectors ......................... 1-2 1.1.3 Dual Loop System ......................................................... 1-4 1.1.4 Pressure-Type Sensor .................................................. 1-4 1.1.5 Thermocouple System .................................................. 1-4

1.2 FIRE ZONES ................................................................................. 1-5 1.2.1 Hot And Cool Zones ...................................................... 1-6 1.2.2 Fireproof Bulkheads ...................................................... 1-6 1.2.3 Engine Fire Prevention .................................................. 1-6 1.2.4 Cockpit and Cabin Interiors. .......................................... 1-7

1.3 SMOKE DETECTION ...................................................................... 1-7 1.3.1 Carbon Monoxide Detectors .......................................... 1-7 1.3.2 Photoelectric Smoke Detectors. .................................... 1-8 1.3.3 Ionization Type Smoke Detector. .................................. 1-8

1.4 FIRE EXTINGUISHING .................................................................... 1-9 1.4.1 Extinguishing System .................................................... 1-10 1.4.2 Directional Flow Control Valves (2 Way Valves) ............ 1-12 1.4.3 Fire Extinguishant Container ......................................... 1-12 1.4.4 Toilet Compartment Systems ........................................ 1-13 1.4.5 Warnings And Indications .............................................. 1-13 1.4.6 Hand Held (Portable) Fire Extinguishers ....................... 1-14

1.5 SYSTEM TESTS ............................................................................ 1-14

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1 FIRE PROTECTION As fire is one of the most dangerous threats to an aircraft, manufacturers and operators will install a variety of overheat, fire and smoke detection devices as well as extinguishing equipment. Different types of aircraft require different levels of equipment, depending on the demands of the relevant airworthiness authorities. 1.1 FIRE DETECTION AND WARNING Overheat and fire protection systems on larger, modern aircraft do not rely on observation by crew members as a primary method of fire detection. An ideal fire protection system will include as many as possible of the following features: 1. Must not cause false warnings under any circumstances. 2. Rapid indication of the fire and its accurate location. 3. Accurate indication that the fire is out 4. Indication that the fire has re-ignited 5. Continuous indication for the duration of the fire 6. Means of testing the detection system electrically, from the cockpit. 7. Detectors that are proof against oil, water, vibration and high temperatures. 8. Detectors that are light and easily located throughout the aircraft 9. Detector circuitry that depends on basic power supplies only. 10. Minimum electrical current draw during 'stand-by' when not indicating. 11. Each system should indicate, via a cockpit light, showing location and an

audible alarm system. 12. A separate system for each engine. The size of modern airliners makes the detection of heat, fire and smoke difficult, so most have detection systems installed in the most likely places that they may occur. These can include the engine bays, electrical compartments, cargo holds, hot air duct runs and wheel bays. All these areas must be separately indicated to the flight deck, so that the crew can take suitable action. 1.1.1 Thermal Switch Detectors This system is a spot-type system that uses a number of thermally activated switches to warn of fire (Figure 1). They are mounted in parallel and are connected in series with the warning light. This parallel connection allows the remainder of the system to work even when one indicator has failed. The indicators operate using a bi-metallic thermoswitch that closes when heated to a high temperature and, just as importantly, goes open circuit again when the heat is removed. A thermoswitch spot detector is shown in Figure 2




Thermoswitch Type Fire Detection System Figure 1

Thermoswitch Spot Detector

Figure 2 1.1.2 Continuous Loop (Fire Wire) Detectors This method permits more complete coverage of a fire hazard area than any type of spot-type of temperature detectors. The continuous loop uses the principle of capacitance and resistance to indicate a rise in temperature at any point along the length of the detector loop. The commonest type has a stainless steel or Inconel outer tube, an inner pure nickel wire surrounded by ceramic beads wetted by eutectic salt. The effect of this design is that a rise in temperature causes a sharp fall in electrical resistance, as well as a rise in capacitance.


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Once the detection unit senses this effect, anywhere along the wire, it will cause an overheat warning to be generated. This continuous loop system is often referred to as a 'firewire' system.The advantage of a firewire system is that a loop can cover the complete powerplant, (Figure 3) within its cowling so that an overheat or fire will be detected quickly no matter where it starts. The firewire will also re-set the control box to remove the warning when the temperature falls below the limit temperature.

Fire Wire Layout Figure 3

Firewire elements are attached to the airframe structure with quick release clips approximately 6 apart and 4 from the end fittings. The element is supported in clips with a rubber grommet to prevent rubbing and to help damp out vibrations. (Figure 4). Care is taken to eliminate strain on the element as excessive bending could result in work hardening of the capillary.

Fire Wire Clips and Connections Figure 4




1.1.3 Dual Loop System Most aircraft use the dual loop system of indication. Each sensing circuit has dual sensing loops. Each Loop A and Loop B is independent of each other. When the loop selector switch is set to BOTH, both loops must detect a fire condition before the warning system is activated. If only one loop detects a fire the associated loop fault light will illuminate. If the selector is switched to a single loop (A or B) full fire warnings will activate if the selected loop senses a fire condition. Pressing the loop test button simulates a fire condition on the respective loop. This is done by earthing the inner electrode of the loop which functionally checks the system and checks the continuity of the loop. 1.1.4 Pressure-Type Sensor The pressure type detection system uses a continuous loop for the detection element. This loop is made from sealed stainless steel tube that contains an element which absorbs gas when it is cold but releases the gas when it is heated. This tube is connected to a pressure switch that will close when the pressure reaches a pre-determined level. The commonest make of this type of system is the Systron-Donner system which uses a centre titanium centre wire and the expansion of both helium and hydrogen gas to give the two-stage warnings. Whilst the firewire system actuates when any part of the loop reaches the limit temperature, the pressure type system will actuate in two different ways. If a localised fire occurs, the hydrogen gas is released and its pressure closes the pressure switch which will set off the warning system, however, if the temperature over a larger area rises to a lower level than a fire warning the helium expands and closes the pressure switch to activate the system warning. 1.1.5 Thermocouple System The thermocouple warning system operates on a different principle from the thermal switch system. A thermocouple depends on the rate of temperature rise and will not give a warning when an engine slowly overheats or a short circuit developes. The system normally consists of the thermocouples, a relay box and a warning system. Figure 5 shows a typical thermocouple. The thermocouple is constructed of two dissimilar metals such as chromel and constantin. The point where these metals are joined will be exposed to the heat and is called the hit junction. There is also a reference junction, which is insulated and enclosed in a dead air space. A metal sheath surrounds the thermocouple for protection without obstructing the air flow to the hot junction.


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If the temperature rises rapidly the thermocouple produces a voltage because of the temperature difference between the hot junction and the reference junction. If both junctions are heated at the same rate as is normal with a gradual rise in engine temperature, no voltage will be produced.

Thermocouple Figure 5

If there is a fire situation the hot junction will heat much more quickly than the reference junction. The voltage produced will activate the detector circuit and the warning signals will be sent to the cockpit warning panels. 1.2 FIRE ZONES On light aircraft, the only protection against fire is a stainless steel or titanium bulkhead (firewall), dividing the engine bay from the cabin and the rest of the aircraft. Larger aircraft have the complete engine cowlings isolated from the airframe/wing assemblies and, in addition, aircraft cowlings can be divided into a number of 'fire zones', each one usually having its own warning and extinguishing system. The types of zone dictate what type of protection that they receive, for example, light aircraft have piston engines and hence, due to the high flow of air through the bay, have no fire protection and depend on isolating the engine of fuel to put out any fire. The example has four zones around the engine only two of which have firewires and extinguishing.




1.2.1 Hot And Cool Zones Engines are usually split into hot and cool zones (Figure 6). The hot zone comprises the combustion chamber turbines and exhaust areas, the cool zone comprises the intake, compressors and accessory drives.

Engine Fire Zones Figure 6

1.2.2 Fireproof Bulkheads These prevent fire from spreading to other areas. Auxillary power units and tail mounted engines are normally contained within such bulkhead compartments separating them from the rest of the airframe. The engine pylons also contain a firewall to separate the engine from the wing. These are made from titanium or stainless steel and all joints are sealed with fireproof sealants 1.2.3 Engine Fire Prevention There are a number of techniques used to help prevent a fire occurring around engines. These are, the use of flameproof or flame resistant materials, use of bonding strips to prevent arcing, drainage of spilt fuel/oil and efficient cooling. All pipes which carry fuel, oil or hydraulic fluids are made fire resistant and all electrical components and connections are made flame proof.


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It is essential that a fire staring in any zone is contained within that zone and is not allowed to spread to any other part of the aircraft. The engine cowlings form a natural container but they are usually made from light alloy and would not contain a ground fire for long. In flight however cooling airflows through the cowlings provide sufficient cooling to render the cowlings fireproof. The fireproof bulkheads and any cowling that has no cooling air flow are usually made from titanium or stainless steel. 1.2.4 Cockpit and Cabin Interiors. All wool, cotton and synthetic fabrics used in interior trim are treated to render them flame resistant. Tests conducted have shown that whilst the foam used in seat cushions is flammable, if covered with a flame-resistant fabric, there is little danger of fire from accidental contact with a cigarette, for example. Fire protection for the aircraft interior is usually provided by hand-held extinguishers. Various types are available including, Water, CO2 and Dry Powder. Each type is best used on one kind of fire but may be used on other kinds. It is best to be sure which is safe to use on which type of fire. 1.3 SMOKE DETECTION A smoke detection system monitors certain areas of the aircraft for the presence of smoke, which is could be indicative of a fire condition. These may include, cargo and baggage compartments and the toilets of transport category aircraft. A smoke detection system is used where the type of fire anticipated is expected to generate a substantial amount of smoke before temperature changes are sufficient to actuate a heat/fire detection system. 1.3.1 Carbon Monoxide Detectors The presence of Carbon Monoxide (CO), or Nitrous Oxides (N2O), is dangerous to flight crew and passengers alike and may indicate a fire condition as it is a by product of combustion. Detection of the presence of either or both of these gases could be the earliest warning of a possible dangerous situation. Carbon Monoxide is very dangerous, firstly due to the minute amount required to cause loss of attention and headaches, (this is approximately 2 parts in 10,000). It is colourless, odourless, tasteless and a non-irritant. Carbon Monoxide detectors are usually used in cabin and cockpit areas. The detector is usually a small card with a transparent pocket containing silica gel crystals that have been treated with a chemical, which changes colour to green or black when they come into contact with carbon monoxide.




1.3.2 Photoelectric Smoke Detectors. Air from the monitored compartment is drawn through the detector chamber and a light beam is shone on it. A photoelectric cell installed in the chamber senses the light that is refracted by the smoke particles. The photocell is installed in a bridge circuit that measures any changes, in the amount of current that it conducts. Figure 7 shows a typical photoelectric smoke detector.

Photo Electirc Smoke Detector Figure 7

When there is no smoke in the chamber air, no light is refracted and the photocell produces a reference current. When smoke is in the chamber air, some of the light is refracted and sensed by the photocell. Its conductivity changes, changing the amount of current. These changes in current are amplified and used to initiate a smoke warning signal. 1.3.3 Ionization Type Smoke Detector. A small amount of radioactive material is mounted on the side of the detector chamber. This material bombards the oxygen and nitrogen molecules in the air flowing through the chamber and ionizes it to the extent that a reference current can flow across the chamber through the ionised gas to an external circuit.


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Ionisation Type Smoke Detector Figure 8

Smoke flowing through the chamber changes the level of ionisation and decreases the current. When the current reduces to a specific level the external circuit initiates a smoke warning signal. Figure 8 shows a typical ionisation smoke detectot.

Flame Detectors This system uses a photoelectric cell to detect a sharp rise in light, such as that from a flame in a closed bay. 1.4 FIRE EXTINGUISHING There are a variety of aircraft and ramp extinguishing agents. Their use depends upon several variables such as location, proximity to personnel, environment, possible sources of fire, etc. There are integral extinguishing systems on board the aircraft as well as hand held extinguishers




1.4.1 Extinguishing System Aircraft that have an integral fire extinguisher system have a system similar to the arrangement shown in Figure 9. There are a number of pressurised bottles with extinguishant inside and each bottle has two explosive cartridges, (squibs), which can be fired from the flight deck. Each bottle can feed either the port or starboard engines through a crossfeed. The extinguishant is fed through a series of pipelines and valves to the outlet nozzles and tubes. In some aircraft, fixed systems may also be provided for the protection of landing gear wheel bays and baggage compartments. These systems may be independent of each other. They may be fully automatic or require the air crew to initiate them when a fire is indicated.

Basic Aircraft Extinguishing System

Figure 9 On multi-engine aircraft there may be one extinguisher bottle provided for each engine or one bottle may feed 2 engines (Figure 10). There is always usually a facility for cross feeding to another engine should the need arise.


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Dual Container System Figure 10

Two bottles giving either two 'shots', to a single engine or, one 'shot' each to either engine (Figure 11). The bottle condition is indicated either through a pressure gauge on each bottle, or a red/green sectioned gauge showing red when the bottle is empty or its pressure is low as well as a discharge indication on the associated fire control panel I the cockpit.

Typical 2 Shot System

Figure 11




There may also be pop up indicators to indicate that the squib has been fired. A pressure switch may also be fitted which gives an electrical indication to the cockpit control panel when the pressure drops to a pre-determined level. Each bottle will have protection against overpressure using a 'rupture disc', which fails if the bottle pressure becomes excessive due to overheating. 1.4.2 Directional Flow Control Valves (2 Way Valves) These valves are non return valves designed for use in a crossfeed system to allow the contents of one or several extinguishers to be directed into any one engine (or compartment). The valves prevent the reverse flow of the extinguishant into the other bottle or engine. 1.4.3 Fire Extinguishant Container Figure 12 shows a typical extinguishant container. The cartridge is electrically ignited which drives the cartridge cutter into the disc which on rupture releases the extinguishant. The strainer prevents any of the broken disc from entering the distribution system.

Fire Extinguisher Bottle Figure 12


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The safety plug is connected by a pipeline to a red indicator disc on the outside of the compartment. If the gas pressure increases due to an increase in the compartment temperature that the bottle is located in, the fusable safety plug melts at a pre-determined temperature and the bottle contents are discharged overboard. As the bottle discharges overboard it blows out the red indicator. The gauge shows the pressure of the extinguishant in the container. 1.4.4 Toilet Compartment Systems Small, automatic units will often be found in the toilet waste bins, where they will discharge themselves when a heat source is sensed in the region of 75 degrees centigrade. A fusible type plug will melt allowing the contents to discharge. Most aircraft with this system fitted do not generate any indications to the cockpit or attendants panel if the system was activated. Some systems have a visible temperature strip which can be checked before each flight, or by the cabin crew in flight. 1.4.5 Warnings And Indications Once a fire has been detected in the engine bay (or compartment being sensed) a signal is generated by the firewire element and this signal is sent to a control unit. The control unit processes the signal and sends a signal to the cockpit CWP, associated power lever handle, and the fire control panel. The CWP red Fire warning caption light illuminates for the affected engine (or compartment) as well as the master warning lights and audio warnings. The Affected power lever handle and fire extinguisher handle on the overhead console also illuminate red. To activate the extinguishant, the red fire handle is pulled to arm the system and then the squib button is pressed to fire the bottle. If after the bottle contents have exhausted and the fire indication remains, the second squib button is pressed to fire the contents of the other bottle into the same affected engine (or compartment). Some aircraft activate the extinguishers differently. The bottle may be fired by pressing the affected fire button on the fire panel. If the fire remains a cross feed switch is activated which opens a crossfeed valve and the same fire button is repressed to fire the other bottles contents into the same affected system. Once discharged an amber DISCH caption on the fire control panel will indicate when the corresponding bottle is empty. These captions are usually electrically activated Whatever the method of operation of the extinguisher system, the same basic principle applies. The contents of each bottle, can be cross fed into the affected area, that is on fire.




1.4.6 Hand Held (Portable) Fire Extinguishers Each aircraft must carry portable fire extinguishers for use by the cabin crew in the event of a fire. These are positioned in various places within the cabin with easy access to the crew. The amount and location depends on the type of aircraft and its size. Halon extinguishers contain a gas that interrupts the chemical reaction that takes place when fuels burn. These types of extinguishers are often used to protect valuable electrical equipment since they leave no residue to clean up. Halon extinguishers have a limited range, usually 4 to 6 feet. The initial application of Halon should be made at the base of the fire, even after the flames have been extinguished Carbon Dioxide fire extinguishers disperses the gas quickly, these extinguishers are only effective from 3 to 8 feet. The carbon dioxide is stored as a compressed liquid in the extinguisher; as it expands, it cools the surrounding air. The cooling will often cause ice to form around the horn where the gas is expelled from the extinguisher. They are primarily used to extinguish electrical fires in the cabin and cockpit. The CO2 can be aimed at the fire and discharged using a trigger.

A dry powder fire extinguisher use compressed nitrogen to expel a dry powder such as sodium bicarbonate or potassium bicarbonate. They can be used on most fires but should never be used on the flight deck, due to lack of visibility and interference with some electrical equipment caused by the powder.. Water extinguishers are also fitted to some aircraft and should be used to put out fires in ordinary combustibles, such as wood and paper. The hand held extinguishers are subject to periodic maintenance. The extinguisher is checked for its weight. This is stamped on the neck of the bottle and indicates its charged weight. If the weight is below the set limits, it is to be replaced. 1.5 SYSTEM TESTS All extinguishing systems have a method of testing their serviceability. This can vary from weighing the complete cylinder off-aircraft, (which will have the correct 'full' weight marked on it), through to the bottle having a gauge with safe and low-pressure sectors marked on it. Figure 13 shows an engine extinguisher with a fitted gauge. Other more sophisticated systems have internal pressure switches fitted to the bottle, which will notify the flight deck of the loss of bottle pressure, (or discharge), via a warning light, magnetic indicator etc.


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Regardless of the system, all bottles and squibs have a life, after which they have to be removed and returned to the manufacturer for maintenance.

Fire Bottle With Pressure Gauge

Figure 13

Fire System Test Switch A test switch is available for each system. When pressed all warning lights and audio warnings are checked. If a light fails to illuminate it will normally indicate a bulb filament failure.

Fire Wire Loop Test A test switch on the cockpit fire panel is available to test each sensing element loop. When selected the continuity of each circuit is checked. If the system is serviceable the Loop caption(s) will illuminate. If the caption(s) do not illuminate there is a fault in the system.

Squib-Test . A squib test button is available to check the continuity of the discharge heads for each of the fire extinguisher bottles. When pressed a squib warning light or magnetic indicator will illuminate if the system is serviceable. No illumination means that there is a fault in the system. The current used during the squib test is at a much lower value than that required to fire the squib.




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easa part 66 - module 11.08 - fire protection

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protection systems

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extinguishing system

smoke detection devices

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