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What is the purpose of a bleed air system?
a. To supply air from the engine compressor section or other sources to pneumatically operated systems.
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What are three sources of bleed air used to operate systems on jet aircraft?
a. Aircraft engine(s); ground air cart; and GTCs, GTUs, or APUs.
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List the components of a bleed air system.
a. Check valves, shutoff valve, wing isolation or body crossover valves, flow control valves, pressure regulating valves, bleed air ducting, and the necessary controls.
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What is the purpose of a ground-air-connection check valve?
a. Prevent the escape of bleed air from the system.
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What happens to the system shutoff valve if power to the solenoid is interrupted?
a. The fail-safe feature causes the air to pass through the deenergized solenoid plunger and pushes the piston, thus, closing the butterfly valve.
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Why is velocity greatest at the venturi throat?
a. The airflow rate through the venturi throat increases so that the same amount of air at the inlet can pass through the narrow throat.
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What function does a pressure limiter serve in a bleed air system?
a. To protect downstream components from excessive pressure.
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What are the factors that limit a flow control valve?
a. Inlet pressure and inlet temperature.
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What material(s) are used for high-pressure/high-temperature ducting?
a. Stainless steel.
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To ensure a good airtight seal when installing a V-band clamp, what action should you take?
a. Tap the clamp with a rawhide or plastic-faced mallet.
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Why should the bottom bolts be installed first on a bolted flange duct?
a. To cradle or support the gasket in place.
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What type lubricant can be used on beaded duct sleeves to aid in installation?
a. Water.
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List three components that compensate for thermal expansion.
a. Any three of the following: expansion joint (bellows), thermal compensator, universal joints, loops, horseshoe bends, and offsets.
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An operational check of the bleed air system consists of what?
a. An electrical check to ensure opening and closing of bleed air valves when the control switches are placed to the corresponding positions.
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When is a leakage check test performed on a bleed air system?
a. After maintenance on the bleed air system requiring the removal or installation of system components.
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What air sources can be used to perform a leakage test?
a. Aircraft engines, mobile ground air carts, and GTCs or APUs.
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What are the 2 most commonly used methods for detecting leaks?
a. Hand survey and pressure decay.
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Why should bleed air ducting insulation be removed when discoloration of the aircraft structure is found?
a. The bleed air leak may not be in the immediate area of the discoloration.
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What malfunction could an over-speeding cooling turbine indicate?
a. A drastic decrease in cooling efficiency.
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How does low bleed air system pressure cause high temperature in the cockpit?
a. The cooling turbine is not receiving sufficient airflow to produce effective cooling.
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Match the components in column B with the precooler functions in column A.
- "Column B" (a)Jet pump modulating and shutoff valve, (b)Pneumatic thermostat, (c)Temperature control circuit
- "Column A" b(1)Senses temperature of precooled bleed air, c(2)Positions the modulating control valve, a(3)Controls the airflow through the jet pump
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Describe the operation of a heat exchanger.
a. Hot bleed air enters the heat exchanger and passes through passages that are cooled by ram air flowing across them.
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What is the purpose of the water aspirator and regenerative heat exchanger?
a. To provide additional cooling of the bleed air to reduce the excessive turbine discharge temperatures.
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How does the compressor turbines section increase cooling efficiency?
a. By increasing the bleed air pressure before sending air pressure to the expansion turbine.
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What are three benefits of ceramic bearings over steel bearings?
a. Any 3 of the following: much harder than steel, full ceramic bearings can be operated at temperatures up to 1800°F, smoother and more uniformly round than steel bearings, require little or in some cases no lubrication, lighter than steel bearings of the same size, they are highly corrosion resistant, nonmagnetic, electrically nonconductive, and thermally insulating.
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A cooling turbine unit had been operated for several hours without replenishment of the oil supply. You are inspecting the unit and notice the turbine oil is slightly darker than normal and has a few dark particles in it. What actions do you take? Why?
a. The turbine unit should be removed and replaced. Although darkening of the oil due to overtime operation is normal, any noticeable particles, (regardless of the nature) usually are causes for removal of the turbine from service.
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Explain how the electronic temperature control anti-icing system operates.
a. A sensor transmits the temperature signal to the controller. The controller causes the actuator to position the anti-icing valve according to the temperature sensed by the sensor.
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Explain briefly how the ice control screen anti-icing system operates.
a. When an ice control screen begins to ice up, it slows down the air flow through the turbine. This causes the air temperature to rise and melt the ice.
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A write up in the aircraft forms states that after several hours of system operation the cabin area started receiving fog, which turned to snow. Should the water separator be replaced? Explain.
a. Not necessarily. There could be several reasons for this. The separator may not be removing the moisture because the condenser bag is freezing. In addition, the condenser bag may be dirty or the water drain may be clogged. In either of these cases, the water separator won’t need replacing.
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What air source is used for cabin ventilation?
a. Atmospheric (ram) air.
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What is the purpose of the ground cooling ejector valve?
a. Controls bleed air used to draw ram air across the heat exchanger on the ground.
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What is the purpose of the flow limiting venture?
a. Prevent pressure surges from reaching the turbine and also to prevent a complete loss of system pressure through a ruptured disc.
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When the pilot is receiving full cold air in the cockpit, what are the positions of the dualtemperature mixing valve butterflies?
a. The butterfly leading to the cooling turbine opens and the butterfly in the hot bleed air ducting closes.
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Match the systems components in column B with the function in column A.
- "Column B" (a)Water separator, (b)Anti-ice valve, (c)Anti-ice controller, (d)Rheostat, (e)Control box, (f)Sensor, (g)Manual temperature limiter, (h)Temperature control switch
- "Column A" c(1)Controls air pressure on the opening diaphragm, b(2)Allows warm air to go to the condenser, a(3)Condenses moisture into water droplets, f(4)Senses temperature changes, d(5)Selects the desired temperature during automatic operations, g(6)Prevents overheating of the system, h(7)Used to select the mode of operation, e(8)Sends a signal to the dual temperature mixing valve
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What component is used to start and stop the bomber ACS?
a. The ACS pressure regulator and shutoff valve.
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What is the purpose of the catalytic filter?
a. Removes any contaminants in the air supply.
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When a decrease in control pressure is sensed by the flow control sensor, in what direction does the flow control valve modulate? Why?
a. Towards the open position; to allow more airflow due to a decrease in air pressure.
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What components absorb the power produced by the expansion turbine?
a. Compressor turbine and cooling air fan.
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How does the CTCS controller provide temperature control of the upper and lower cabin?
a. With input signals from the zone temperature sensor, zone supply air temperature sensor, and the zone temperature selector.
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What unit controls bleed air temperature to 450°F?
a. The primary heat exchanger system.
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What is the purpose of the turbine bypass valve?
a. Directs airflow through, or around the cooling turbines, depending on the temperature of the air.
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What is the purpose of the air conditioning diverter valve?
a. Directs airflow to either the flight station, cargo compartment, or both.
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Explain the operation of the flight station alternate air shutoff valve.
a. The valve diverts all the air from the right ACS to the cargo compartment when in one position. When the valve is in the other position, the flight station gets 38 percent of the air from the right system.
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How is compartment temperature controlled by the temperature control rheostat?
a.In automatic, the temperature selector is used to unbalance the bridge circuit. This causes the temperature control box to signal the temperature control valve to increase or decrease compartment temperature as selected.
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Why would not the fan in the temperature sensor assembly operate when the temperature control switch is in manual?
a. Because the fan operates whenever the temperature control system is in automatic mode of operation.
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What unit is energized at the same time as the floor heat shutoff valve?
a. The floor heat modulating valve solenoid.
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How does the floor heat pneumatic thermostat control the modulating valve?
a. A bimetallic element expands and contracts, which allows pressure to the servo assembly to open and close the modulating valve.
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State the functions of the following cargo heating system components.(A)Cargo floor heat shutoff valve, (B)Venturi, (C)Floor heat modulating valve, (D)Pneumatic control thermostat, (E)Pneumatic temperature anticipator, (F)Necessary ducting
- (a)Cargo floor heat shutoff valve; operates with the floor heat switch to make air available for under floor heating.
- (b)Venturi; limits the flow of bleed air.
- (c)Pneumatic modulating and shutoff valve; regulates the pressure available in response to a signal from either the thermostat or anticipator when the controlling solenoid is energized; functions as a shutoff when the controlling solenoid is deenergized.
- (d)Pneumatic control thermostat; provides temperature and pressure control signals to the temperature modulating and shutoff valve.
- (e)Pneumatic temperature anticipator; provides pneumatic signals to the floor temperature modulating and shutoff valve in response to rapid temperature changes but remains inoperative during steadystate temperature conditions.
- (f)Necessary ducting; delivers the air as needed.
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What bodily sensation would the pilot feel when pulling 2 positive Gs?
a. There is the sensation of being pushed down hard into the seat. In addition, the arms and legs feel as if heavy weights are attached to them.
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What effect does negative G-force have on the body?
a. Causes the blood to rush to the head. If excessive negative G-forces are encountered, a red out may occur. The effect of the negative G force may even go as far as rupturing blood vessels in the head.
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Excessive positive Gs have what effect on the body?
a. The pressure supplied by the heart is not great enough to pump an adequate supply of blood to the head. As a result, the pilot experiences grayout, blackout, and unconsciousness.
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Explain the automatic operation of the anti-G suit system?
a. It works automatically when one or more engines are running and the suit is connected. The system consists of a tap-off (supply line), an anti-G valve, the necessary lines and fitting, and a suit attachment fitting. This suit attachment fitting is either a single quick disconnect or a composite quick disconnect. The suit itself contains the other half of a quick disconnect similar to an oxygen mask-to-hose connection. The pilot plugs the suit into a quick disconnect and air pressure is supplied to the suit in proportion to the G-forces encountered.
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During flight, a positive 4 Gs are encountered and the anti-G suit inflates. What happens when the aircraft returns to level flight?
a. The activating weight is raised by the spring tension, closing the demand valve and opening the exhaust valve. Suit pressure then bleeds off through the open exhaust port.
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Explain the two methods used for defrosting aircraft windshields?
a. (1)Non-electrostatic application (NESA) glass, (2)Passing heated air across the inside of the windshield keeps it clear.
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A pilot moves the defog lever from the foot heat position to defog. From where does the defog source of air come?
a. Comes from the conditioned air entering the cockpit; it is the same air that is used for foot heat.
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A pilot’s write up states the windshield was only partially cleared of fog during flight. What should you check?
a. To control the heat of a window by means of a bridge circuit between the sensing element and the controller amplifier.
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What is the function of the controller amplifier in the NESA anti-ice circuit?
a. To control the heat of a window by means of a bridge circuit between the sensing element and the controller amplifier.
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What can be checked on the individual window units in the NESA glass system?
a. Their resistance.
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What is the purpose of a thermal snap switch in the NESA window anti-icing circuit?
a. To remove power from the window after approximately 10 minutes if the temperature is 70°F.
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How does the rain removal system keep the windshield clear?
a. By directing a stream of bleed air across the windshield to carry the particles away before they reach the windshield.
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Why is a venturi needed in the rain removal system?
a. To prevent the primary heat exchanger from overheating.
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How does the rain removal duct drain valve operate?
a. When the rain removal system is turned on, the air pressure closes the drain valve. When the system is turned off, a spring opens the drain valve.
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During an operational check of the rain removal system, you notice the paint around the windshield is blistered. What caused this problem?
a. The rain removal system was left on too long.
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During an operational check of the rain removal system, water is initially sprayed from the nozzles. What malfunction, if any, is indicated?
a. The rain removal duct drain valve is not operating properly, allowing water to collect in the rain removal duct.
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What system increases air flow through the heat exchanger during takeoff?
a. The ground cooling ejector system.
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What function does the air-to-water heat exchanger serve?
a. When needed, it assists the secondary heat exchanger in removing the increased heat from the compressor.
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When will the high pressure check valve operate?
a. When the warm air modulating valve opens, a high pressure, existing below the high pressure check valve, pushes the valve open.
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Why should the normal-reverse selector switch be placed in the REVERSE position when the pressure selector switch is placed in the OFF position?
a. This allows conditioned air to hit the electronic packs first when the system is first operated.
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If the air conditioning system went full hot during automatic operation, what components should you consider checking?
a. The temperature controller, the temperature sensor, or the control rheostat.
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During air conditioning system operation, higher than normal air temperature was found. What component(s) may have caused this condition?
a. The ground ejector valve failing to open, the ground air ejector nozzles broken, cracked heat exchanger, low system pressure or a bad modulating valve.
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During manual and automatic operation of the air-conditioning system, the cabin temperature could not be cooled and was accompanied by excessive noise. The failure of what unit is the most probable cause of this condition?
a. Failure of the turbine.
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List the three pressurization ranges.
a. Unpressurized, isobaric, and differential.
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Explain how the isobaric section of the pressure regulator keeps the aircraft unpressurized below 8,000 feet.
a. The isobaric aneroid is compressed, causing a metering valve to open and bleed off control chanber pressure. This drop in pressure causes the outflow valve to remain open up to 8,000 feet.
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State the purpose of the dual-differential pressure regulator’s change-over solenoid.
a. The solenoid opens to vent control pressure from the low-differential metering valve to atmosphere.
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How would the safety outflow valve operation be affected if a pneumatic relay were not used?
a. They would open at different times.
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Setting the cabin altitude selector at 10,000 feet causes the unpressurized range to go up to how many feet.
a. 10,000 feet.
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What is one disadvantage of the manual control valve?
a. When it is being used and the cabin pressure reaches an undesirable state, the pilot must readjust the valve manually.
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List the three positions of the pressure regulator test handle.
a. FLIGHT—Normal, DIFFERENTIAL TEST, TEST ONLY—ALL OFF.
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If you find two canopy seals ruptured on one aircraft, what unit probably failed to operate properly?
a. The canopy seal pressure regulator.
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A predetermined altitude setting of 9,000 feet is accomplished through the action of what components in the cabin pressure controller?
a. The cabin altitude selector coil spring, rocker arm, fulcrum, and isobaric aneroid.
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A pressure buildup in the lower chamber of the cabin pressure controller is accomplished through the actions of what components?
a. The rate filter and rate selector metering valve.
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What safety components are incorporated into the cabin pressurization system?
a. A manual control valve and pneumatic relay.
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The cabin selector knob was set at 5,000 feet during flight, but the aircraft pressurized from the ground up. What components would cause this condition?
a. A ruptured aneroid, a stuck closed isobaric metering valve, or a leaking sensing line between the cabin pressure controller and the pneumatic relay.
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What is the primary hazard involved in pressurization tests?
a. The structural integrity of the aircraft.
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Explain the hazards of nasal or sinus congestion during pressurization tests.
a. High pressure from pressurization tests enters sinus cavities and ear canals and is trapped. As cabin pressure is released, the trapped pressure causes pain and a possible rupture.
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Explain why the rate selector valve should be placed in the start position before starting the tester.
a. To prevent uncontrolled pressure from being applied to the aircraft cabin.
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Explain why the canopy seal pressure must be closely monitored.
a. To prevent air leaks around the canopy and rupturing of the canopy seal.
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