Fire Protection Quiz 10.2024 PDF

Fire Protection (15.20) Learning Objectives 15.20 Explain the operation of detection and extinguishing systems (Level 2). 2024-07-23 B1-15b Gas Turbine Engine Page 258 of 290 CASA Part 66 - Training Materials Onl...

Fire Protection (15.20) Learning Objectives 15.20 Explain the operation of detection and extinguishing systems (Level 2). 2024-07-23 B1-15b Gas Turbine Engine Page 258 of 290 CASA Part 66 - Training Materials Only  Engine failure and severe re during take-off Engine Fire Detection Systems Several varieties of re surveillance systems are available for re detection purposes. The more common types are: Spot systems Thermal switch system Thermocouple system Optical re detection system Continuous loop systems Pressure type sensors. 2024-07-23 B1-15b Gas Turbine Engine Page 260 of 290 CASA Part 66 - Training Materials Only  Spot or Unit Type Detection Systems With spot or unit type systems, individual re detectors are placed in areas where a re is likely to occur but will only give warnings if there is an overheat condition at that exact spot. Thermal Switch Detector Thermal switches are also known as thermostat switches or spot detectors. The actual switch is mounted inside a stainless-steel housing. If a re begins, the switch housing heats up and elongates, causing the contact points to close. To adjust a thermal switch, the housing must be heated to a speci ed temperature and then a tension adjustment is turned in or out until the contacts just close. In most cases, this adjustment is set by the detector manufacturer and is not adjusted in the eld. The thermal switch can be either a single-wire or dual-wire operation. Aviation Australia Thermal switch detector The thermal switches are connected in parallel with each other, but in series with the indicator light in the ight deck. Any one switch, if grounded, can give a warning. A test switch in the ight deck provides power to a relay that in turn provides a ground to the warning light. Note that this only tests the continuity of the circuit and not the thermal switch capability. 2024-07-23 B1-15b Gas Turbine Engine Page 261 of 290 CASA Part 66 - Training Materials Only  Aviation Australia Thermal switch re detection circuit System Operation In the illustration above, all the switches are bolted to the aircraft frame, which connects one of the contacts of the switch to earth. The other contact of each of the switches is connected in parallel to the coil of relay RL1. Should any switch close, a current path is made for the coil of RL1. When energised, the contacts of RL1 complete a current path for the bell and red light. When the crew has been alerted, they can stop the bell from ringing by pressing the BELL CANCEL button. This action energises RL2, breaking the bell’s current path and completing its own coil’s current path. The BELL CANCEL button can be released, but RL2 remains energised until the re warning disappears. This system normally operates off the 28-V DC battery bus. Testing The test button completes an earth connection to R1 via all the wiring connecting the thermal switches. This checks the wiring for continuity. The bell should ring and the red light illuminate. If the BELL CANCEL button is pressed, the bell stops, but the red light remains illuminated. Individual switches can be tested for correct operation (continuity) by using an ohmmeter. 2024-07-23 B1-15b Gas Turbine Engine Page 262 of 290 CASA Part 66 - Training Materials Only  Double Loop The two-wire thermal switch can withstand one fault, either an open or short circuit, without causing a false warning. For example, if the ground loop develops a short, no warning occurs because the loop is already grounded. If the power loop shorts, the rapid increase in current ow trips a relay that causes the powered loop to become the ground and the grounded loop to become the powered. All the detectors are connected in parallel between two complete loops of wiring. One leg of the circuit supplies current to detectors, while the other leg is a path to ground. Aviation Australia Double loop (two wire) thermal switch circuit Aviation Australia Thermal switch caution notice 2024-07-23 B1-15b Gas Turbine Engine Page 263 of 290 CASA Part 66 - Training Materials Only  Thermocouple Fire or Overheat Detection Sensors Thermocouple type, rate of temperature rise, re and overheat systems are other types of spot detector. The thermocouple is constructed of two dissimilar metals, such as Chromel and constantan. Thermocouples are used where the temperature at a speci c location within the compartment could rise faster than the overall compartment temperature. These systems are often installed in engine compartments, where normal operating temperatures are quite high, but the rise to this temperature is gradual. When the hot junction is exposed to heat from an external source, an increase in current is obtained. The increase in current is directly proportional to the temperature difference between the hot and cold junctions. When the current reaches a preset level, warning indication is activated. This system is used in such areas as engines and in the aircraft pneumatic air bleed system. Again, for the purpose of redundancy, this system operates off the aircraft’s 28-V DC system. Aviation Australia Thermocouple spot detector In a thermocouple system, the detector is triggered by the rate of temperature rise, as opposed to the thermal switch, which detects a preset temperature. A typical thermocouple system has one or more thermocouples, called active thermocouples. These are placed in re zones around an engine, while a separate thermocouple, called a reference thermocouple, is placed in a dead air space between two insulated blocks. 2024-07-23 B1-15b Gas Turbine Engine Page 264 of 290 CASA Part 66 - Training Materials Only  ©Aviation Australia A thermocouple re detection system Under normal circumstances, the temperature of the air surrounding the reference thermocouple and the active thermocouples is relatively even, and no resultant current is produced. However, when a re occurs, the difference in temperature produces a current in the circuit and activates a warning. System Test Selection of the test function passes current through a heater around the test thermocouple. Its output causes the system to operate. The test checks the continuity of the circuit and is usually the only test applied to these systems. Each individual thermocouple is not tested normally. 2024-07-23 B1-15b Gas Turbine Engine Page 265 of 290 CASA Part 66 - Training Materials Only  Continuous-Loop Fire Detection Systems Continuous-loop systems work on the same basic principle as spot type systems, but a single switch in the form of a long tube is used instead of several spot detector switches. The small-diameter tube is tted all around the engine nacelle and allows complete coverage of the engine. These systems use different types of elements and control systems manufactured by the Fenwal and Walter Kidde companies. Large commercial aircraft almost exclusively use continuous thermal- sensing elements for power plant protection. The elements are also called re wires and are used primarily for engine re detection and overheat detection of bleed air systems. Fire wires and are used primarily for engine re detection and overheat detection of bleed air systems Fire elements come in different lengths and are identi ed by part number. There may be several sections joined together to make up the one element for an engine. These sections are joined to each other and the aircraft wiring by small plugs. The element is positioned around the engine or other compartment and attached by clamps, sleeves or grommets. When replacing a re wire, ensure the new path of wire matches the wire being replaced. 2024-07-23 B1-15b Gas Turbine Engine Page 266 of 290 CASA Part 66 - Training Materials Only  Fenwal Single-Conductor Element The Fenwal system uses a single conductor element. A thin-walled tube made from the alloy Inconel is lled with a compound. Embedded in the centre of the lling compound is a single nickel conductor. The lling compound can be in different forms. Two examples are: 1. Ceramic beads wetted with a eutectic salt. The salt’s melting point is low and its resistance lowers drastically when it melts, but will increase again when solidi ed. 2. Aluminium oxide suspended in brous glass. The resistance of this compound lowers with heat and its dielectric qualities improve, so the capacitance of the re wire is higher as temperature increases. At normal temperatures, the eutectic salt core material prevents electrical current from owing. With an increase in temperature, the core resistance drops and current ows between the signal wire and ground, energising the alarm system. When the re has been extinguished or critical temperature lowered, the system automatically returns to standby, ready to detect another over-temperature condition. The control unit senses the current ow, which produces a signal to actuate the warning system. Aviation Australia Continuous loop detection system - single conductor 2024-07-23 B1-15b Gas Turbine Engine Page 267 of 290 CASA Part 66 - Training Materials Only  Aviation Australia Single wire overheat sensing element circuit diagram 2024-07-23 B1-15b Gas Turbine Engine Page 268 of 290 CASA Part 66 - Training Materials Only  Kidde Two-Conductor Element The two-conductor element tube is made from the same alloy as the single-conductor element tube and is about the same size. Two nickel conductors are embedded in the lling compound, which is referred to as a thermistor material, having a negative temperature coef cient of resistance. That is, an increase in temperature decreases resistance. As the temperature of the core increases, electrical resistance to the ground decreases. The re detection control unit monitors this resistance. If the resistance decreases to the overheat set point, an overheat indication occurs in the ight deck. If the resistance decreases further to the re set point, a re warning occurs. As with the Fenwal system, when the re has been extinguished or critical temperature lowered the system will automatically return to standby, ready to detect another over temperature condition. In addition to re and overheat detection, the Kidde system can supply nacelle temperature data to the aircraft condition monitoring function of the Aircraft In- ight monitoring System. Continuous loop detection system - double conductor Testing Testing is usually carried out through the aircraft’s re test system, which is done through the control unit. Always use the correct test procedure (as per the aircraft manual) when testing continuous-loop systems. Most test functions test the integrity of the circuit and the re wires. 2024-07-23 B1-15b Gas Turbine Engine Page 269 of 290 CASA Part 66 - Training Materials Only  Pneumatic Continuous Loop Systems Two types of pneumatic continuous-loop systems are commonly used for re and overheat detection, with similar operation: Lindberg System Systron-Donner System. Lindberg System The Lindberg System consists of a stainless steel tube with an inert gas inside and a discrete material capable of absorbing a portion of the gas. The amount of gas the material can absorb varies with temperature, and when the discrete material is heated, it releases the absorbed gas, increasing the pressure in the tube. One end of the tube is sealed and the other is connected to a responder that consists of a pressure-sensing element and a set of electrical contacts. When the contacts are forced closed by the increased pressure in the tube, a warning system is activated (lights and/or audible warning). Aviation Australia Lindberg pneumatic continuous-loop system To test a Lindberg System, low-voltage AC is sent through the stainless steel outer casing, heating the sensing element until the gas is released from the discrete material and eventually causing the warning system to activate. When the test switch is released, the sensing element cools and the discrete material re-absorbs the inert gas, decreasing the pressure and opening the switch contacts in the transponder. During testing, the entire system is functionally tested, encompassing the control unit, wiring and temperature sensor. 2024-07-23 B1-15b Gas Turbine Engine Page 270 of 290 CASA Part 66 - Training Materials Only  Aviation Australia Lindberg pneumatic continuous-loop system circuit diagram 2024-07-23 B1-15b Gas Turbine Engine Page 271 of 290 CASA Part 66 - Training Materials Only  Systron-Donner System The Systron-Donner System is also a pneumatic continuous system incorporating a stainless steel tube lled with helium gas under pressure, but with a titanium wire running through the centre. The titanium wire acts as the gas absorption material because it contains a quantity of hydrogen. The Systron-Donner System provides a warning if an average OVERHEAT condition is detected, in addition to a FIRE warning. At normal temperatures, the helium gas pressure has insuf cient force to close the diaphragm switch. However, when the AVERAGE TEMPERATURE along the length of the tube reaches an OVERHEAT level, the gas pressure increases enough to close the diaphragm switch contacts, activating the alarm. The FIRE warning function is provided by the titanium wire. When this wire is exposed to localised heating, such as a re or a bleed air leak, it releases hydrogen gas, which again increases the overall pressure within the tube, triggering the warning system. After the re is extinguished, the hydrogen gas is re-absorbed by the titanium wire and the responder contacts break, resetting the alarm (switching it off). A typical system consists of two separate sensing loops for redundancy. Both loops are required to sense a re or overheat before an alarm will sound; however, if one loop fails (integrity switch opens), the system control box (typically computerised) isolates the defective loop and recon gures to a single-loop operation using the good loop. It is also part of all pre- ight checklists for ight crew and/or maintenance crews to perform a re detection system integrity test before each and every engine start to con rm system serviceability before operating the aircraft engines. Pneumatic re detection system installation 2024-07-23 B1-15b Gas Turbine Engine Page 272 of 290 CASA Part 66 - Training Materials Only  To check system integrity, the responder unit contains an integrity switch which has its contacts held closed by the normal gas pressure exerted by the helium. When the system is serviceable and helium pressure is satisfactory (no leaks), depressing the FIRE TEST switch activates the re warning alarms. However, if the helium pressure is below normal as a result of a leak in the system, depressing the FIRE TEST switch has no result – the test voltage is not applied to the warning circuit because there is an open circuit at the integrity switch contacts. Systron-Donner pneumatic re detection system 2024-07-23 B1-15b Gas Turbine Engine Page 273 of 290 CASA Part 66 - Training Materials Only  Inspection and Maintenance Installation of Elements When installing an element, you must comply with the following: Bends can be no sharper than a 1-in. radius. The grommet must protect the element from the clamp. The clamp should not touch the wire. The split in the grommet must be placed so that the element will not pull through. The element must not rub or touch anything. Continuous loop re sensing wires support bracket 2024-07-23 B1-15b Gas Turbine Engine Page 274 of 290 CASA Part 66 - Training Materials Only  Inspection of Elements Damage to the element can cause system failure or a false warning. Damage can be caused by poor installation or damage due to being stood on or having tools or other items placed or dropped on it. Ensure not to kink or overbend re wires, which can cause internal wire breakage, making the system inoperative. When inspecting an element, you must also ensure that: The element is not broken, there are no cracks in the surface and no part of the surface is chafed. Indentations in the surface do not exceed parameters detailed in the aircraft manual. Grommets are in good condition. All plugs are tight and lock-wired. If not, inspect for cleanliness and internal damage. Continuous loop re sensing wires installation 2024-07-23 B1-15b Gas Turbine Engine Page 275 of 290 CASA Part 66 - Training Materials Only  Fire Extinguisher Systems Purpose of Fire Extinguisher Systems Engine re extinguisher systems are used to remove re from the aircraft. Most gas turbine-powered aircraft have on-board re extinguisher systems that remove oxygen. Engine re and overheat protection includes the following: Engines and nacelles Pylon area APU and APU compartment. 2024-07-23 B1-15b Gas Turbine Engine Page 276 of 290 CASA Part 66 - Training Materials Only  Halogenated Hydrocarbons A halogen element is part of the group that contains chlorine, uorine, bromine and iodine. Some hydrocarbons combine with halogens to produce very effective re extinguishing agents that extinguish res by excluding oxygen from the re source and by chemically interfering with the combustion process. Because of changing regulations and developing environmental impact data, you should keep abreast of updates pertaining to the use of halogenated hydrocarbons as re extinguishing agents. It is important for you, as an aircraft maintenance engineer, to be aware of EPA, CASA and EASA regulations governing the use and disposal of CFCs. Improper handling or disposal of halogenated hydrocarbons can lead to civil and criminal penalties. Extinguishing agent Halon 1301 properties include: Colourless Odourless Displaces oxygen Chemically reacts with the exothermal process Non-corrosive Non-toxic Ozone depleting. Typical engine re extinguisher system 2024-07-23 B1-15b Gas Turbine Engine Page 277 of 290 CASA Part 66 - Training Materials Only  High Rate of Discharge Systems High rate of discharge (HRD) is the term applied to the re extinguishing systems found in most modern turbine engine aircraft. A typical HRD system consists of a container to hold the extinguishing agent, at least one bonnet assembly and a series of high-pressure feed lines. The containers used in an HRD system are typically made of steel and spherically shaped. Smaller containers generally have two openings: one for the bonnet assembly or operating head, and the other for a fusible safety plug. Larger containers are usually equipped with two bonnet assemblies. High rate discharge bottle Each container is partially lled with an extinguishing agent, such as Halon 1301, and sealed with a frangible disc. Once sealed, the container is pressurised with dry nitrogen. A container pressure gauge is provided so you can quickly reference the container pressure. The bonnet assembly contains an electrically ignited discharge cartridge, or squib, which res a projectile into the frangible disc. Once the disc breaks, the pressurised nitrogen forces the extinguishing agent out of the sphere. To prevent the broken disc fragments from getting into the distribution lines, a strainer is also installed in the bonnet assembly. A thermal fuse is installed in each bottle, which will melt and release the contents if the bottle is subjected to high temperatures. 2024-07-23 B1-15b Gas Turbine Engine Page 278 of 290 CASA Part 66 - Training Materials Only  2-shot high rate of discharge (HRD) re extinguisher Two indicating discs are placed in an easily visible position on the outside skin of the aircraft. The red disc is connected by plumbing to the bottle (thermal) relief valve. If the relief valve releases pressure, the red disc blows out. If this occurs, the bottle has to be serviced. A yellow disc is connected by plumbing and a restrictor to the bottle outlet. If the bottle discharges normally, the yellow disc blows out. If this occurs, the bottle has to be changed. Fire extinguisher discharge indicator discs 2024-07-23 B1-15b Gas Turbine Engine Page 279 of 290 CASA Part 66 - Training Materials Only  Fire extinguisher discharge indicator discs If either the red or yellow disc is missing, the system should be inspected to determine the cause. If the bottle has a pressure gauge, check the pressure indication. If the bottle is not equipped with a pressure gauge, weigh the bottle. If the pressure or weight is below normal, the bottle should be serviced or replaced before ight. Extinguishing Agent Identi cation Tape Extinguishing agent pipelines are identi ed by brown tape. This tape also has diamond symbols and the words Fire Protection. Extinguishing agent identi cation tape 2024-07-23 B1-15b Gas Turbine Engine Page 280 of 290 CASA Part 66 - Training Materials Only  Fire Panels Purpose of Fire Panels Relevant handle lights may ash or illuminate steadily, depending on aircraft design. Some aircraft handles ash for engine turbine area overheat and illuminate steadily for turbine re. All use red for re warning and amber for overheat indication. Flight deck re extinguisher panel (B737) All aircraft have the means to test the engine and APU re protection systems. A test should be carried out before starting the APU or engines, and the test procedure is different for each aircraft type. The test con rms the integrity of the re detection system without ring the bottles. Normally, the test does not con rm whether the bottle or squib is serviceable. In some systems, the test function closes the fuel and hydraulic re shut-off valves. Crew Procedure for an Engine Fire In the event of an engine re, the crew activates the necessary re handle. When the handle is pulled or activated, it closes off the fuel and hydraulics. Depending on the aircraft, it may also deactivate other systems, such as pneumatics, electrics and the thrust reverser systems. The next movement of the handles causes the re extinguishers to be activated. 2024-07-23 B1-15b Gas Turbine Engine Page 281 of 290 CASA Part 66 - Training Materials Only  System Operation All Transport category aircraft have at least one re extinguisher bottle for each engine, with cross- feed plumbing so the bottle can be discharged into another engine if a second shot is needed to ght the re. The discharge of the rst bottle is called rst shot, and the discharge of the next bottle is called second shot. The electrical switching to discharge the bottles always includes protection against inadvertent ring. This can be: A guarded switch A tee handle which has to be turned 90° before it can be pulled to re the bottle. All re handles contain a red re warning light. This allows quick intuitive identi cation of the system requiring immediate corrective action. It also helps to prevent a mistaken selection because it is the illuminated handle that needs to be pulled. Fire extinguisher electrical circuit 2024-07-23 B1-15b Gas Turbine Engine Page 282 of 290 CASA Part 66 - Training Materials Only  Fire and Overheat Detection Fire and Overheat Detection System Features Detection systems must be capable of rapidly detecting a localised re or overheat condition and indicating the area in which corrective action is required. Detectors must not automatically operate re extinguishing units, although they may be used to shut down power or fuel to certain areas or components. An ideal re detector system includes as many of the following features as possible: No false warnings under any ight or ground condition Rapid indication and accurate location of a re Accurate indication that the re is out Indication that a re has re-ignited Continuous indication for the duration of a re A means for electrically testing the detector system from the ight deck Detectors that resist damage from exposure to oil, water, vibration, extreme temperatures or handling Detectors that are lightweight and easily adaptable to any mounting position Detector circuitry that operates directly from an aircraft power system (battery) Minimum electrical current requirements when not indicating a re Ability to turn on a ight deck light corresponding to each detector and indicating the location of the re, and an audible alarm A separate re detection system for each engine. Computer-aided automatic operation of Auxiliary Power Unit (APU) re extinguishing units is used in some modern transport category aircraft, but only while on the ground. 2024-07-23 B1-15b Gas Turbine Engine Page 259 of 290 CASA Part 66 - Training Materials Only  Fire Extinguisher System Operation The diagram below illustrates a twin-engine aircraft system with one bottle in each engine nacelle (each bottle has two outlets), operated by a pull lever which also runs with the motorised gate valve low-pressure cock closed. Fire extinguisher electrical circuit Assume the right engine is on re; the crew receive a warning through the aircraft’s re detection system. The bottle selector switch should be in the rst shot position. The pilot pulls the tee handle: Power is provided through the re handle and relayed to the closed side of the low-pressure fuel cock motor. This closes off fuel to the right engine. The tee handle switch completes a current path to the rst shot cartridge of the right re bottle, which discharges into the right engine. 2024-07-23 B1-15b Gas Turbine Engine Page 283 of 290 CASA Part 66 - Training Materials Only  If the re persists: The pilot selects the re extinguisher selector switch to second shot, with the handle still pulled out. A current path is made to the left re bottle second shot cartridge. The left bottle discharges into the right engine, and the right engine ow valve prevents its contents going into the empty right bottle. 2024-07-23 B1-15b Gas Turbine Engine Page 284 of 290 CASA Part 66 - Training Materials Only  APU Fire System APU Fire Detection and Extinguishing Most modern commercial aircraft have a separate APU re detection and extinguisher system. This is because the APU is required to operate during ground operations. The APU re detection system is usually a single or double re loop detection system, which only detects res and not overheat situations. The loop is connected to an APU Fire Detection Module located in the main electronics area of the aircraft. Fire warnings are provided both in the ight deck and in a remote location of the aircraft – usually on the nose landing gear or in the main wheel well. In ight, if a re is detected in the APU compartment, a normal ight deck re alarm occurs, including: Red warning light Ringing re bell. If a re is detected in the APU compartment while the aircraft is on the ground, the normal ight deck re indications occur, plus the following: A horn sounds outside the aircraft. The APU automatically shuts down. In some aircraft, if the re persists, the extinguisher automatically discharges. Aircraft tted with an APU have a separate APU re system. As well as the ight deck APU re panel, most large aircraft are equipped with a remote APU re panel. The remote panel allows ground staff to control an APU re without the need to access the ight deck. Example of an APU remote (ground) re panel (B727) 2024-07-23 B1-15b Gas Turbine Engine Page 285 of 290 CASA Part 66 - Training Materials Only  Example of an APU remote (ground) re panel access (F28) Common locations for the remote panel include: Nose landing gear wheel well Main landing gear wheel well Refuelling panel Aft fuselage, APU access. Example of an APU remote re panel (B737) 2024-07-23 B1-15b Gas Turbine Engine Page 286 of 290 CASA Part 66 - Training Materials Only  Precautions Fire Protection Systems Precautions Never use an ordinary ohmmeter to check HRD re extinguisher circuits. It can re the cartridge (squib). Use only a safety ohmmeter. Safety ohmmeter Ensure all associated circuit breakers are pulled before working on the aircraft re protection system. Ensure no static charge is present on your person or tools prior to touching re bottle squibs. 2024-07-23 B1-15b Gas Turbine Engine Page 287 of 290 CASA Part 66 - Training Materials Only  Static spark caution A squib’s electrical terminals must be shorted anytime a connector is removed. Squib electrical warning Eye protection should be worn when handling squibs. 2024-07-23 B1-15b Gas Turbine Engine Page 288 of 290 CASA Part 66 - Training Materials Only  Caution wear eye protection Don’t fool with squib cartridges; they are an explosive device and must be handled carefully and treated with caution. Squibs may be sensitive to shock, impact, friction, electrostatic discharge, high pressure or high temperature. They may ignite and explode, releasing toxic fumes, heat, a shock wave and container fragments. 2024-07-23 B1-15b Gas Turbine Engine Page 289 of 290 CASA Part 66 - Training Materials Only  Ground Run Fire ghting Sometimes it may be necessary to extinguish a re if it occurs on start-up or during an engine ground run. It may not be necessary to use the aircraft’s HRD re protection system. Normally, a dry chemical powder type re extinguishing agent is used by the engineer assisting and monitoring the ground run from outside the aircraft. After the re has been extinguished, the engine should be motored by the starter to reduce the EGT as rapidly as possible to below 500 °C. The engine gas path should be washed down after the engine has cooled suf ciently to reduce the likelihood of thermal shock to hot section parts. The engine compressor wash should be performed in accordance with the engine/airframe maintenance manual. Portable re extinguishers 2024-07-23 B1-15b Gas Turbine Engine Page 290 of 290 CASA Part 66 - Training Materials Only