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To supply air from the engine compressor section or other sources to pneumatically operated systems.
Aircraft engine(s); ground air cart; and GTCs, GTUs, or APUs.
List the components of a bleed air system.
Check valves, shutoff valve, wing isolation or body crossover valves, flow control valves, pressure regulating valves, bleed air ducting, and the necessary controls.
The fail-safe feature causes the air to pass through the deenergized solenoid plunger and pushes the piston, thus, closing the butterfly valve.
The airflow rate through the venturi throat increases so that the same amount of air at the inlet can pass through the narrow throat.
What are the factors that limit a flow control valve?
The flow cont shutoff vlv fails to close when the switch for the cont solenoid vlv is opened. A chk reveals no pwr is at the solenoid vlv. You have pressure to the top of the actuator diaphragm. What the possible causes of malfunction?
Either the control solenoid valve (J), or the poppet valve (G) is leaking and causing control pressure to be applied to the actuator.
Why should the bottom bolts be installed first on a bolted flange duct?
An electrical check to ensure opening and closing of bleed air valves when the control switches are placed to the corresponding positions.
After maintenance on the bleed air system requiring the removal or installation of system components.
Why should bleed air ducting insulation be removed when discoloration of the aircraft structure is found?
What malfunction could an over-speeding cooling turbine indicate?
Hot bleed air enters the heat exchanger and passes through passages that are cooled by ram air flowing across them.
To provide additional cooling of the bleed air to reduce the excessive turbine discharge temperatures.
How does the compressor turbines section increase cooling efficiency?
The design of the top and bump foils, the diameter, and the length and speed of the rotating shaft.
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?
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.
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.
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.
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.
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.
An air-conditioning and pressurization system has a water separator bypass. A write up states that an excess moisture condition exists in the cabin area at all times during ACS operation. Should the water separator bereplaced? Explain.
Not necessarily. There can be several reasons for this. The bypass valve may be stuck open. Also, the solenoid operated control valve or the aneroid may be stuck.
An ACS has a ventilation syste. A malfunction of the ACS, emergency ventilation was selected. The write up further states that air entered the cabin area through the aircraft (cabin) outlets. Is this normal? Explain.
Yes. During emergency ventilation, ram air is now coming into the crew area through the aircraft air outlets.
What component is used to start and stop the bomber ACS?
When a decrease in control pressure is sensed by the flow control sensor, in what direction does the flow control valve modulate? Why?
With input signals from the zone temperature sensor, zone supply air temperature sensor, and the zone temperature selector.
What unit controls bleed air temperature to 450°F?
Directs airflow through, or around the cooling turbines, depending on the temperature of the air.
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.
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.
Why would not the fan in the temperature sensor assembly operate when the temperature control switch is in manual?
Because the fan operates whenever the temperature control system is in automatic mode of operation.
How does the floor heat pneumatic thermostat control the modulating valve?
A bimetallic element expands and contracts, which allows pressure to the servo assembly to open and close the modulating valve.
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.
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.
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.
. The pilot plugs the suit into a quick disconnect and air pressure is supplied to the suit in proportion to the G-forces encountered.
During flight, a positive 4 Gs are encountered and the anti-G suit inflates. What happens when the aircraft returns to level flight?
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.
(1) Non-electrostatic application (NESA) glass.
(2) Passing heated air across the inside of the windshield keeps it clear.
A pilot moves the defog lever from the foot heat position to defog. From where does the defog
source of air come?
A pilot’s write up states the windshield was only partially cleared of fog during flight. What
should you check?
To control the heat of a window by means of a bridge circuit between the sensing element and the controller amplifier.
What is the purpose of a thermal snap switch in the NESA window anti-icing circuit?
By directing a stream of bleed air across the windshield to carry the particles away before they reach the windshield.
Why is a venturi needed in the rain removal system?
To prevent the primary heat exchanger from overheating.
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.
During an operational check of the rain removal system, you notice the paint around the
windshield is blistered. What caused this problem?
During an operational check of the rain removal system, water is initially sprayed from the
nozzles. What malfunction, if any, is indicated?
The rain removal duct drain valve is not operating properly, allowing water to collect in the rain removal duct.
When upstream anti-icing air pressure is too low to provide the regulated air pressure, what is the position of the control valve?
After the anti-icing air flows through the wing’s double skin passages, it returns to the plenum.
What happens to this air next?
Part of the air returns to the jet pump as recirculating air, the rest goes overboard.
What function does the air-to-water heat exchanger serve?
When needed, it assists the secondary heat exchanger in removing the increased heat from the compressor.
When the warm air modulating valve opens, a high pressure, existing below the high pressure check valve, pushes the valve open.
Why should the normal-reverse selector switch be placed in the REVERSE position when the
pressure selector switch is placed in the OFF position?
This allows conditioned air to hit the electronic packs first when the system is first operated.
If the air conditioning system went full hot during automatic operation, what components should you consider checking?
The temperature controller, the temperature sensor, or the control rheostat.
During air conditioning system operation, higher than normal air temperature was found. What component(s) may have caused this condition?
The ground ejector valve failing to open, the ground air ejector nozzles broken, cracked heat exchanger, low system pressure or a bad modulating valve.
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?
Using figure 3–1, compute the cabin altitude when the aircraft is flying at 15,000 feet in the
Explain how the isobaric section of the pressure regulator keeps the aircraft unpressurized below 8,000 feet.
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.
The solenoid opens to vent control pressure from the low-differential metering valve to atmosphere.
How would the safety outflow valve operation be affected if a pneumatic relay were not used?
Setting the cabin altitude selector at 10,000 feet causes the unpressurized range to go up to how many feet.
When it is being used and the cabin pressure reaches an undesirable state, the pilot must readjust the valve manually.
List the three positions of the pressure regulator test handle.
FLIGHT—Normal, DIFFERENTIAL TEST, TEST ONLY—ALL OFF.
If you find two canopy seals ruptured on one aircraft, what unit probably failed to operate
A predetermined altitude setting of 9,000 feet is accomplished through the action of what
components in the cabin pressure controller?
A pressure buildup in the lower chamber of the cabin pressure controller is accomplished through the actions of what components?
A manual control valve and pneumatic relay.
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 ruptured aneroid, a stuck closed isobaric metering valve, or a leaking sensing line between the cabin pressure controller and the pneumatic relay.
Explain the hazards of nasal or sinus congestion during pressurization tests.
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.
Explain why the rate selector valve should be placed in the start position before starting the tester.
What is leakage in cubic feet per minute leakage, if the flowmeter float setting is as shown in
figure 3–8, the blower pressure is 2 psig, and the temperature of the tester outlet air is 50°F?
The flowmeter float setting is as shown in figure 3–8, and blower output pressure is 10 psig.
What would be flow in pounds per minute if the temperature is 70° and barometric pressure is 13 psia?
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