Aviation Maintenance: Environmental Systems
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1
Why are the cabins of most turbine-powered aircraft pressurized? (AM.II.G.K1)
These aircraft fly at such high altitudes that supplemental oxygen would be needed for the occupants if the cabins were not pressurized.
2
Where does the pressurizing air come from on most turbine-powered aircraft? (AM.II.G.K1)
From air bled from one of the engine compressors.
3
Where does the pressurizing air come from on most smaller reciprocating-engine-powered aircraft? (AM.II.G.K1)
From the engine turbocharger.
4
What determines the amount of pressurization that an aircraft can use? (AM.II.G.K1)
The structural strength of the aircraft cabin.
5
What is meant by the isobaric mode of cabin pressurization? (AM.II.G.K1)
The isobaric mode of cabin pressurization is the mode that keeps the cabin altitude constant as the aircraft changes its flight altitude.
6
What is meant by the constant differential mode of cabin pressurization? (AM.II.G.K1)
After the pressure in the aircraft cabin reaches the maximum value allowed by structural considerations, the constant differential mode of operation holds the pressure inside the cabin a constant amount above the outside air pressure.
7
How is high-temperature bleed air cooled down to safe temperatures for aircraft heating? (AM.IIG.K2)
The air is passed through a heat exchanger.
8
How are aircraft instruments and avionics cooled? (AM.II.G.K3)
By routing air-conditioned air over the instruments and avionics, or by electrically operated cooling fans.
9
What is the danger of a leak in an exhaust system cabin heater? (AM.IIG.K4)
Exhaust gases contain carbon monoxide (CO), a colorless, odorless, gas that can cause incapacitation or death to the aircraft occupants.
10
How can an exhaust system be checked for leaks? (AM.II.G.K4)
Pressurize it with the discharge from a vacuum cleaner and wipe the outside of the system with a soap solution. Any leak will cause bubbles to form.
11
How can you tell that there is carbon monoxide in the aircraft cabin? (AM.II. G.K4)
Indicator crystals in a CO detector will change color, from a normally bright color to a dark color. At lethal levels of CO they will turn black. Electronic CO detectors provide both visual and aural alerts to the crew.
12
Where does the warm air come from that is used to heat the cabin of most small single-engine reciprocating-engine-powered aircraft? (AM.II.G.K4)
From a shroud around the engine muffler.
13
Where does the fuel used in an aircraft combustion heater come from? (AM.II.G.K5)
From the aircraft fuel tanks.
14
What happens to a combustion heater if the flow of ventilating air is restricted? (AM.II.G.K5)
If the ventilating air is restricted and the temperature reaches a preset value, the limit switch will cause the fuel to be shut off to the heater.
15
What regulates the temperature in an aircraft cabin that is heated with a combustion heater? (AM.II.G.K5)
A thermostat senses the cabin temperature and cycles the fuel valve on or off to maintain the temperature at the desired value.
16
What maintenance is required for a combustion heater? (AM.II.G.K5)
Clean the fuel filters and check for fuel leaks. Pressure test the combustion chamber to check for leaks.
17
How is the heat removed from an aircraft cabin with a vapor-cycle air conditioning system? (AM.II.G.K6)
The cabin heat is absorbed by the refrigerant in the evaporator, then carried outside the aircraft where it is given up to the outside air in the condenser.
18
What produces the cool air in a vapor-cycle air conditioning system? (AM.II.G.K6)
Warm cabin air is blown across the evaporator, where its heat is transferred into the refrigerant. The air that leaves the evaporator is cool.
19
What is used as the refrigerant in a vapor-cycle air conditioning system? (AM.II.G.K6)
A Freon-type liquid refrigerant known as Refrigerant 12, or the more environmentally friendly R-134a.
20
What is the state of the refrigerant as it leaves the compressor? (AM.II.G.K6)
It is a high-pressure gas.
21
What is the state of the refrigerant as it leaves the condenser? (AM.II.G.K6)
It is a high-pressure liquid.
22
What is the state of the refrigerant as it leaves the thermostatic expansion valve? (AM.II.G.K6)
It is a low-pressure liquid.
23
What is the state of the refrigerant as it leaves the evaporator? (AM.I.G.K6)
It is a low-pressure vapor.
24
How is the compressor lubricated? (AM.II.G.K6)
Refrigeration oil is mixed with the refrigerant and it circulates through the compressor and the entire system.
25
What is the function of the thermostatic expansion valve? (AM..G. K6)
It meters just enough liquid refrigerant into the evaporator that all of it will be evaporated by the time it leaves the evaporator coils.
26
How is refrigerant put into the system? (AM.II.G.K6)
It is put into the svstem through service valves on the low side of the system using a manifold gauge set.
27
How should the components in the low side of a properly operating vapor-cycle cooling system feel? (AM.II.G.K6)
They should feel cool.
28
How is a vapor-cycle cooling system checked for refrigerant leaks? (AM.II.G.K6)
Hold the probe of an electronic leak detector below any suspect fitting or component. If there is a leak, the tone of the sound produced by the detector will change.
29
What safety equipment should be worn when charging a vapor-cycle cooling system? (AM.II.G.K6)
A safety face shield that protects the entire face.
30
What are two types of air conditioning systems that may be installed on an aircraft? (AM.II.G.K6)
Air-cycle systems and vapor-cycle systems.
31
Where does the warm air come from that is used to heat the cabin of a large jet transport aircraft? (AM.II.G.K7)
Warm engine compressor bleed air is used.
32
Where is the first place the hot compressor bleed air gives up some of its heat in an air-cycle cooling system? (AM.II.G.K7)
In the primary heat exchanger.
33
What is the function of the air-cycle machine in an air-cycle cooling system? (AM.II.G.K7)
The centrifugal compressor increases the pressure and temperature of the bleed air. This high temperature air gives up some of its heat in the secondary heat exchanger, and a great deal more as it drives the expansion turbine. It leaves the expansion turbine as cold
34
Why must air-cycle air conditioning systems incorporate a water separator? (AM.II.G.K7)
The rapid cooling of the air in the expansion turbine causes moisture to condense in the into the cabin. form of fog. This moisture is trapped in the moisture separator before the air is released
35
How is the temperature of the air produced by an air-cycle cooling system controlled? (AM.II.G.K7)
By a temperature control valve which mixes hot engine compressor bleed air with cold air from the expansion turbine.
36
How is cabin pressure controlled in a pressurized aircraft? (AM.II.G.K8)
More pressure than is needed is pumped into the aircraft cabin, and the pressure controller modulates the outflow valve to maintain the correct pressure in the cabin.
37
What is the function of the cabin outflow valve on a pressurized aircraft? (AM.II.G.K8)
The cabin outflow valve, which is controlled by the pressure controller, maintains the correct amount of pressure inside the cabin.
38
What is the function of the cabin pressure safety valve on a pressurized aircraft? (AM.II.G.K8)
The cabin pressure safety valve prevents cabin pressure from exceeding the maximum allowable differential pressure.
39
Why must pressurized aircraft have a negative pressure relief valve? (AM.Il.G.K8)
The structure of an aircraft cabin is not designed to tolerate the inside pressure being lower than the outside pressure.
40
What keeps the cabin of a pressurized aircraft from being pressurized when the aircraft is on the ground? (AM.II.G.K8)
A squat switch on the landing gear holds the safety valve open when the aircraft is on the ground.
41
What are three ways supplemental oxygen can be carried in an aircraft? (AM.II.G.K9)
As a high-pressure gas, in its liquid form, and as a solid in the form of a chemical candle.
42
What is a continuous-flow oxygen system? (AM.II.G.K9)
An oxygen system that continuously flows a metered amount of oxygen into the mask.
43
What is a pressure-demand oxygen system? (AM.II.G.K9)
An oxygen system that flows oxygen to the mask only when the wearer of the mask inhales. Above a specified altitude, the regulator meters oxygen under pressure into the mask when the wearer inhales.
44
What are the two main gases that make up our atmosphere? (AM.II.G.K10)
Nitrogen and oxygen.
45
What is used to check an oxygen system for leaks? (AM.II. G.K10)
A special leak-detector liquid that is a form of non-oily soap.
46
Why must fittings in an oxygen system not be tightened to stop a leak when there is pressure on the system? (AM.II.G.K10)
when it is expand resurized, the lin is pad rid he ling thend
47
What kind of gaseous oxygen must be used to service an aircraft oxygen system? (AM.II.G.K10)
Only aviators' breathing oxygen. Hospital oxygen and welding oxygen contain too much moisture to be used.
48
What identification must be stamped on an oxygen bottle carried in an aircraft? (AM.II.G.K10)
The identification DOT 3AA or DOT 3HT, the date of manufacture, and the date of all o the hydrostatic tests.
49
To what pressure and how often should DOT AA oxygen cylinders be hydro-statically tested? (AM.II.G.K10)
They should be tested to 5/3 of their working pressure every three years.
50
To what pressure and how often should DOT 3HT oxygen cylinders be hydro-statically tested, and when should they be retired from service? (AM.I.G.K10)
They should be tested to 3,083 psi every three years and retired from service after 15 years or 4,380 pressurizations, whichever occurs first.
51
What kind of lubricant can be used for installing fittings in an oxygen system component? (AM.II.G.K10)
Teflon tape or a special water-base lubricant.
52
What is used to check for leaks after replacing a fitting in an oxygen system? (AM.II.G.K10)
A special leak-detector liquid that is a form of non-oily soap.
53
What cleaning solutions can be used to clean parts used in an oxygen system? (AM.II.G.K10)
Anhydrous ethyl alcohol, isopropyl alcohol, or freon.
54
What may be used to dry components in an oxygen system after they have been cleaned? (AM.II.G.K10)
Water-pumped dry nitrogen.
55
What may be used to purge the lines in an oxygen system after it has been opened for servicing? (AM.II.G.K10)
Water-pumped dry nitrogen.
56
What must be done before any maintenance can be done on an oxygen system? (AM.II.G.K10)
The oxygen supply must be turned off at the bottle valve.
57
What cautions should be used when performing maintenance on oxygen systems? (AM.II.G.R1)
Follow the instructions in the aircraft maintenance manual, never allow oil on the threads of attaching components, use caution when working around high pressure gas, and use appropriate PPE.
58
Why is it important to use refrigerant recovery equipment when servicing vapor-cycle air-conditioning systems? (AM.II.G.R2)
Refrigerant has been shown to cause damage to the environment and should not be vented into the air.
59
What cautions are to be used when handling, storing, or shipping chemical oxygen generators? (AM.II.G.R3)
Once lit, the generators cannot be extinguished and they produce heat. When not installed in an aircraft, they must be protected from accidental actuation with safety pins and protective covers. They are considered hazardous materials for shipping.
60
What precautions should be taken for the storage, handling, and use of compressed gas cylinder and high-pressure systems? (AM.I.G.R4)
High-pressure cylinders should be stored standing vertically and retained with a strap or chain to prevent them from falling over. A protective cap should be used to cover the valve when not in use. Use appropriate high-pressure cylinder carts and dollies when moving cylinders and never lift a cylinder by the valve or protective cap. Use the correct PPE and follow manufacturer's instructions when servicing aircraft.
61
What is the best way to mitigate risks associated with servicing vapor-cycle refrigerant systems? (AM.II.G.R5)
Follow the aircraft maintenance manual for servicing instructions, proper equipment and tooling, and warnings and cautions provided in the manual.
62
What are some of the dangers associated with maintenance of a combustion heater? (AM.II.G.R6)
Failure to follow the maintenance instructions could lead to carbon monoxide entering the cabin, or the unit catching on fire.
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