Utility System

INTRODUCTION Modern day aircraft fly higher and faster than those of the earlier days of flight. The effects of the atmosphere on the aircrew and aircraft as they fly at high altitudes can have negative impacts on mission completion. Utility systems are in place to counteract physiological symptoms aircrew experience in extreme conditions. INFORMATION: Utility System Fundamentals. Bleed Air System It is important to understand what is meant by bleed air and where bleed air comes from. Bleed air is pressurized air originating from the engine compressor section. The compressing of the air into a confined space causes a tremendous increase in the air temperature as high as 900° F. This design gives a source for high temperature, high-volume and low-pressure air to operate various aircraft pneumatic systems. Many aircraft have utility systems that rely on bleed air to function (fig. 3-45). Some of the applications that use bleed air are: • Pneumatic starting of engines. • Deicing and anti-icing equipment • Cabin pressurization, heating, and cooling Fig. 3-45, Bleed Air System CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 109 Components Bleed air is often bled from the final or highest pressure stage through devices called compressor bleed ports (fig. 3-46), at this point, pressure and air temperature are at a maximum. Bleed air ducts (fig. 3-47) route this air from each engine compressor section, APU or external air source to the aircraft systems. They are constructed of heat resistant materials to protect the airframe, other components and personnel from the excessive temperatures (800 - 900°F). Switches located in the control cabin or cockpit provide a means of isolating the engine bleed air shut off/isolation valves (fig. 3-48) to control air flow into or out of the engine enclosure. Bleed air pressure is sensed by the bleed air pressure regulator located in the bleed air supply duct downstream of the crossover duct isolation check valves. The bleed air pressure regulator maintains the bleed air output within the established tolerances. Check valves are installed in the bleed air system where needed to prevent the reverse flow of air. An external air receptacle (fig. 3-49) is installed as part of the duct system to provide an attachment point for an external source of bleed air. Some aircraft come equipped with an onboard APU. This is a small gas turbine compressor that can provide bleed air for engine starting and operational checks of supported pneumatic systems. Fig. 3-46, Compressor Bleed Ports Fig. 3-47, Bleed Air Ducts Fig.3-48, Bleed Air Shut-off Valve Fig 3-49, External Air Receptacle CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 110 Air Conditioning System (fig. 3-50) When a gas is compressed, it gets hot. When expanded, gas cools, meaning that it transfers heat to the surrounding air. Most turbine-powered aircraft air conditioning systems are based on an Air Cycle Machine (ACM) cooling device, often called the cooling turbine. In large aircraft, the whole environmental heating/cooling system is bundled together, including the bleed air heat source, the ACM, and mixing valves. This bundle is commonly referred to as a “pack.” Packs remove the excessive heat from bleed air to a few degrees above ambient temperature and rapidly expands the air via a cooling turbine to near freezing temperatures. Normally two packs are installed for capacity and redundancy to provide conditioned air for pilot/crew and passenger comfort, equipment cooling, and aircraft pressurization. To control cabin temperature the cooled air from the ACM is simply mixed with unconditioned bleed air. Two or more temperature mixing valves are used for this purpose. The conditioned air is then distributed throughout the aircraft via ducts. Fig. 3-50, Air Conditioning System CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 111 Components The most basic air conditioning system consists of many interrelated components including heat exchangers, which are radiator like devices in a car to help cool the engine. The air conditioning heat exchanger (fig. 3-51) uses ram air to initially cool bleed air. After initially cooled, the air passes through the cooling turbines which cools the air to near freezing temperatures through rapid expansion. The rapid de-compression of the air releases water in the form of moisture. The moisture is removed from the cool air by the water separator (fig.3-52) installed downstream of the cooling turbine. The modulating/temperature mixing valves connects untreated bleed air and conditioned cold air ducts to obtain the desired cabin temperature. The temperature selector/controllers (fig. 3-53) control the positioning of the modulating/temperature mixing valve. The conditioned air is routed through the air ducts for pressurization from the air conditioning system to crew stations, equipment bays and other pressurized compartments. Because of their extreme sizes some larger aircraft come equipped with more than one air conditioning system (left and right side packs). If both packs fail, an emergency ram air inlet valve ventilates the cockpit to allow fresh air to enter the cabin or to remove smoke, vapors, or other hazardous air from failing turbine oil seals. Fig. 3-51, Heat Exchanger Fig. 3-53, Temperature Controller Fig. 3-52, Water Separator CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 112 Pressurization System (fig. 3-54) Pressurization is one of those aircraft systems that is very simple in concept but surprisingly complicated in execution. The principle, of course, is to seal up the airplane’s cabin into a pressure vessel. Air is then pumped in to maintain internal pressure as close as possible to that at sea level in order to create a safe and comfortable environment for crew flying at higher altitudes. This helps to ensure an adequate amount of oxygen is available for breathing. Some aircraft incorporate a cabin pressurization subsystem that will operate automatically when a pressure differential exists inside and outside the aircraft. This is accomplished by the regular release of air through the outflow valve to control the cabin pressure according to a predetermined altitude. Components The efficiency of aircraft pressurization depends on multiple components working in concert to control the internal pressure of the aircraft. The aircrew can select the desired cabin pressure in relation to the aircraft’s actual altitude. The pressurization has four general functions (Table 3-2) controlled by the cabin pressure regulator which automatically positions the outflow valve (fig. 3-55) allowing the escape of pressurized air to maintain cabin pressure within safe structural limits. If the ram air valve is open, the outflow valve with be open to 50% to maintain some pressurization. Table 3-2 Pressurization Functions Function Description Ground Function Fully opens outflow valve on ground Pre-pressurization During takeoff, increases pressure to avoid a surge in cabin during rotation Pressurization in flight Adjusts cabin altitude, and rate of change to provide comfortable flight in conjunction relief valves (positive or negative) Depressurization After touchdown, gradually releases residual overpressure before ground function with dump valve Fig. 3-54, Pressurization System Fig. 3-55, Outflow Valve CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 113 Oxygen System The Human body is dependent on oxygen. As the altitude increases, the consequent decrease in pressure reduces the amount of oxygen the human body can absorb when breathing. To enable flight at high altitudes either the aircraft cabin must be pressurized (normal operation), to replicate the pressure at a lower altitude, or the occupants of the aircraft must be given supplemental oxygen. Depending on the aircraft’s design, oxygen is stored in containers as either liquid or gaseous oxygen or it is created onboard using an on-board oxygen generating system (OBOGS). The oxygen system must be able to supply a non-pressurized aircraft during emergency situations such as loss of cabin pressurization. It can also provide oxygen during high altitude cargo/personnel airdrops when the cargo compartment must be open or for the fighter pilot during combat or aerial refueling operations. Regardless of the style of installed system, the aircrew needs a means of delivering the oxygen for use; this is accomplished using oxygen regulators and oxygen masks. Oxygen Regulator The oxygen regulator (fig. 3-56) serves as the connection between the aircraft’s installed oxygen system to deliver regulated pressure and flow to the aircrew members’ oxygen masks. Internal components automatically combine cabin air and oxygen as needed to provide a proper 21% oxygen concentration to the mask at any altitude. Depending upon the aircraft type, regulators can be constant flow or diluter-demand The constant flow regulator provides the same output pressure or flow regardless of altitude. The regulator is therefore optimized for a specific altitude. At altitudes lower than the designed optimum altitude, it will provide more oxygen than is required. This type of regulator is most often found in non-pressurized aircraft and on portable oxygen systems. A single constant flow regulator can control the oxygen flow to all users. When installed, diluter-demand regulators will be located at each crew position. Depending upon user selection, the diluter-demand regulator can provide 100% oxygen under positive pressure or a mixture of oxygen "diluted" with cabin air. The regulator also works on "demand". That is, the oxygen or air-oxygen mixture only flows into the mask during inhalation. The regulator might be a standalone unit, or it could be incorporated into the mask itself. Fig 3-56, Oxygen Regulator CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 114 Liquid Oxygen (LOX) System Liquid oxygen (LOX) is a pale blue transparent liquid. It uses an evacuated double-walled insulation design converter cylinder (fig. 3-57) to keep the liquid oxygen under pressure at a very low temperature (-297° F). The liquid has an expansion ratio of about 862 to 1, which means a small quantity of LOX can be converted to an enormous amount of gaseous oxygen, resulting in the use of very little storage space compared to that needed for high-pressure gaseous oxygen cylinders. The liquid is nontoxic but will freeze (burn) the skin severely upon contact. Use extreme caution not to touch components containing LOX unless gloves are worn, bare skin would immediately stick and freeze to the metal surface. LOX will react violently when it encounters oil, grease, asphalt, kerosene and any ignition source such as a spark (static electricity). Aircraft LOX servicing (fig. 3-58) should not be done during refueling, defueling, or other maintenance work, which could provide a source of ignition. AFTO Form 134 The AFTO form 134 is stored on the LOX servicing cart and identifies the aircraft, date and amount serviced from each serving cart. This form must be filled out as it is an easy way to identify what aircraft has been serviced with that particular cart in case it is discovered that the LOX from the cart is contaminated LOX. Components (fig.3-59) In the aircraft, oxygen in the liquid state is stored in a container called a converter. This is a double-walled, vacuum-insulated container like the common Thermos bottle. It is necessary to convert LOX into usable gaseous oxygen for crewmembers and/or passengers. The converter is equipped with the necessary valves and tubing inside the container for vaporizing the liquid (converting liquid to gas). From the converter, the extremely low temperature oxygen must travel through a heat exchanger to avoid lung damage. The warmed oxygen is directed to storage cylinders for later usage or to a regulator for immediate use of an oxygen mask. To monitor LOX levels within the converter, the quantity gauge receives a signal from the quantity probe on liquid oxygen converter. This probe senses the amount (quantity) of liquid contained in the converter. This information is transmitted to the quantity gauge by an electrical cable. The quantity gauge is marked in liters from zero to the systems maximum storage capacity (i.e., 0 to 10). Fig. 3-57, Liquid Oxygen Converter Fig. 3-58, LOX Servicing CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 115 Fig. 3-59, LOX Schematic CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 116 Gaseous Oxygen System Gaseous oxygen (GOX) systems are used primarily in large aircraft where space and weight limitations are less important, and the systems are used only periodically. Gaseous oxygen is a colorless, odorless, and tasteless gas at normal atmospheric temperatures. It is stored in high pressure cylinders at pressures near 1,800 psi. Pressure regulators installed in the oxygen system limit the GOX output to safe levels. Delivery of the GOX to the aircrew is accomplished in the same manner as systems that utilize LOX. Associated plumbing, valves and oxygen regulators ensure the aircrew receive oxygen as needed. Portable Oxygen Bottle/Cylinder Portable oxygen systems include walk-around cylinders (fig. 3-60), survival kits, and bailout units. The portable oxygen cylinders provide aircrew a supply of gaseous oxygen to allow movement around unpressurized aircraft for short periods and when conditions require them to use an oxygen system (e.g., smoke in the cabin). Recharging hoses installed on the aircraft allow the aircrew to recharge the bottles from the main oxygen system. On-Board Oxygen Generation System (OBOGS) Due to the limitations present in GOX and LOX, the third-generation system, On-Board Oxygen Generation system (fig. 3-61) was developed. In most aircraft installations, bleed air from already conditioned air is tapped directly to OBOGS. This gives the ability to store or generate an abundance supply of pure oxygen, to regulate, dilute as required, and then is distributed to the pilot/aircrew. The breathable gas is produced on board using a Molecular Sieve Oxygen Generator System (MSOGS) The MSOGS works by separating oxygen from nitrogen and other impurities by means of pressure swing adsorption (PSA) technology. This technique uses a zeolite (natural volcanic mineral) molecular sieve (filter) two bed system which is alternatively pressurized and depressurized to absorb the nitrogen. When one bed is de-pressurized and purged of its nitrogen the other bed is in pressurization cycle producing oxygen enriched breathable gas. This is called the concentrator and is sensed by the oxygen monitor to warn the pilot if there is a low pressure of gas. The concentrator boost pumps provide high-pressure oxygen to recharge portable oxygen bottles in flight in the event of a malfunction. OBOGS presents considerable advantages over LOX, including significant life cycle cost advantages, improves safety, weighs less, and on some aircraft eliminates the need for LOX generation, servicing and storage. Fig. 3-60, Walk-around O2 Cylinder Fig. 3-61, On-Board Oxygen Generation System (OBOGS) CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 117 Fire and Overheat Warning System The fire and overheat warning system help notify aircrew when a potential hazardous or fire condition exists. These detection systems are designed to detect the presence of fires or overheating in zones such as the engine bays or nacelles and to illuminate a warning light in the pilot’s compartment. To detect these fires or overheat conditions units of the system are installed in locations where the greatest possibilities of a fire exist. Components A fire and overheat detection system is used to signal the presence of a fire or overheat condition. Ideally, the system should first indicate an overheat condition well before the malfunction escalates to a fire. Two different detectors used in this system, depending on engine, are the thermal switch and the continuous loop detectors. A thermal switch style system has one or more lights in the pilot’s compartment energized by the aircraft power system and the thermal switches located in the engine areas (fig. 3-62) that control operation of the light(s). The thermal switch system uses a bimetallic thermostat switch design that will expand upon the detection (or set value) of temperature increase to complete an electrical circuit to the warning light. A continuous loop detector (fig. 3-63) permits more complete coverage of a fire hazard area than any type of thermal switch temperature detector. Two widely used types of continuous-loop thermistor type detectors are the Kidde (top) and the Fenwal (bottom) systems. Wires imbedded in an insulating core within a tube prevent a circuit to complete. Reaching the designated temperature range causes the insulating core to experience a change and become more conductive. This completes the circuit and illuminates warning lights in the pilot’s compartment to alert the pilot of the fire or overheat condition. Pilots get aircraft operating status inputs from various indicator (warning, caution, and advisory) lights. The fire/overheat warning indicators are intended to alert the pilot and grab their attention (fig. 3-64). Yellow (or in some cases flashing red) lights are used to indicate an overheat condition exist while a steady red light indicates that a fire has developed. In addition to the lights, some aircraft use an audible warning device that activates at the same time as the lights to get the pilot’s immediate attention. The best time to discover that the fire and overheat warning system does not function properly is before the need for the system arises. Testing system circuit continuity, warning lights and audio signals are accomplished by test switches or buttons located in the cockpit/crew station compartments. Fig. 3-62, Thermal Switch Fig. 3-63, Continuous Loop CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 118 T-handles/Fire/Overheat Warning Panel Fire control T-handles (fig.3-64, 3-65) or fire push button lights used to arm the extinguisher system are centrally located in the cockpit/flight station. The fire detector system will indicate an engine/APU fire by illuminating the MASTER CAUTION light and the light in the respective fire control T-handle or fire push buttons. Pulling the fire control T-handle or pushing the respective engine fire button will electrically arm the extinguisher system and close the fuel shutoff valve stopping the flow of fuel going to that particular engine or APU and stops the bleed air from leaving or entering the engine by closing associated valves. Fig. 3-64, Fire/Overheat Panel Fig. 3-65, Fire/Overheat Panel CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 119 Fire Suppression System The engine fire suppression (extinguisher) system consists of a supply cylinder, explosive squib, and valve strategically located in each aircraft. When an engine fire button is pushed or a T-handle is pulled, the following happens: the engine stops because the fuel control shuts off, the engine is isolated from the aircraft systems, and the fire extinguishing system is armed. Pushing the lens of the PUSH TO EXTINGUISH fire switch or turning the T-handle will activate the squib, expelling all the agent in the cylinder at one time (fig. 3-66). The non-toxic/noncorrosive agent, called Halon, stored in the spherical container on the aircraft is released into the engine/APU enclosure. The agent surrounds the external engine/APU inside the enclosure and extinguishes the fire by excluding oxygen from the area.