A&P Airframe Environmental ACS
To what pressure, and how often should DOT 3AA oxygen cylinders be hydrostatically tested?
3083 PSI every 3 years and retired after 15 years or 4380 cycles whichever occurs first
What is used as the refrigerant in a vapor-cycle air conditioning system?
A freon type liquid known as refrigerant 12 or R-134A
What safety equipment should be worn when charging a vapor cycle cooling system?
A full face shield
What is used to check an oxygen system for leaks?
A special leak-detector liquid that is a form of non-oily soap.
What is meant by the constant differential mode of cabin pressurization?
After the pressure in the cabin reaches the maximum value allowed by structural considerations, this mode holds the pressure inside the cabin at a constant amount above the outside air pressure
What are two types of AC systems that my be installed on an aircraft?
Air cycle and vapor cycle
What cleaning solutions can be used to clean parts used in an oxygen system?
Anhydrous ethyl alcohol, isopropyl, or freon
How is the temperature of the air produced by an air cycle cooling system controlled?
By a temperature control valve which mixes hot engine compressor bleed air with cold air from the expansion turbine
How are aircraft instruments and avionics cooled?
By routing air conditioned air over them or by electric fans
How can you tell that there is carbon monoxide in the aircraft cabin?
By the changes observed in the CO detector indicator, usually bright to dark
What maintenance is required for a combustion heater?
Cleaning fuel filters, check for fuel leaks. Pressure test the combustion chamber to check for leaks
How should the components in the low side of a properly operating vapor cycle cooling system feel?
Cool
What is the state of the refrigerant as it leaves the compressor?
High pressure gas
What is the state of the refrigerant as it leaves the condenser?
High pressure liquid
How is the vapor-cycle cooling system checked for refrigerant leaks?
Hold the probe of an electronic leak detector below any suspect areas. If there is a leak the tone of the sound produced by the detector will change
How is refrigerant put into the system?
It is put into the system through service valves on the low side of the system using a manifold gage set.
What is the function of the thermostatic expansion valve?
It meters just enough liquid refrigerant into the evaporator that all of it will be evaporated by the time it leaves the evaporator coils
What is meant by isobaric mode of cabin pressurization?
Keeps the cabin altitude constant as aircraft changes altitude
What is the state of the refrigerant as it leaves the thermostatic expansion valve?
Low pressure liquid
What is the state of the refrigerant as it leaves the evaporator?
Low pressure vapor
What are the two main gases that make up our atmosphere?
Nitrogen and oxygen
How can an exhaust be checked for leaks?
Pressurize with vacuum discharge pressure and soap/water solution for leak
Where is the first place the hot compressor bleed air gives up some of its heat in an air cycle cooling system?
Primary heat exchanger
How is high temperature bleed air cooled down to safe temperatures for aircraft heating?
The air is passing through a heat exchanger
How is heat removed from an aircraft cabin with a vapor cycle AC system?
The cabin heat is absorbed by the refrigerant in the evaporator, then carried outside where it is given up to the outside air in the condenser
What is the function of the cabin pressure safety valve on a pressurized aircraft?
The cabin pressure safety valve prevents cabin pressure from exceeding the maximum allowable differential pressure
What is the function of the air cycle machine in an air cycle cooling system?
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 even more as it drives the expansion turbine. It leaves the turbine as cold air
What identification must be stamped on an oxygen bottle carried in an aircraft?
The identification DOT 3AA or DOT 3HT, date of manufacture, and date of all hydrostatic test
Why must air cycle air conditioning systems incorporate a water separator?
The rapid cooling of the air in the expansion turbine causes moisture to condense in the form of fog. This moisture is trapped in the separator
Why must pressurized aircraft have a negative pressure relief valve?
The structure of an aircraft cabin is not designed to tolerate the inside pressure being lower than the outside pressure.
What happens to a combustion heater if the flow of ventilating air is restricted?
The temperature will increase, once it hits a preset value the limit switch will turn off the heater
What must be done before any maintenance can be done on an oxygen system?
Turn off the bottle supply valve
What produces the cool air in a vapor cycle AC system?
Warm cabin air is blown across the evaporator where its heat is transferred into the refrigerant. The air that leaves the evaporator is cool
What may be used to dry components in an oxygen system after they have been cleaned?
Water pumped dry nitrogen
What may be used to purge the lines in an oxygen system after it has been opened for servicing?
Water pumped dry nitrogen
Why must fittings in an oxygen system not be tightened to stop a leak when there is pressure on the system?
When the system is pressurized, the tubing expanded slightly. If the fitting is tightened while expanded, it will like when the pressure is reduced
