Oral prep - Pressurization Flashcards
How is cabin pressurization maintained?
Cabin pressurization is maintained by regulating the amount of air leaked overboard through two outflow valves
In terms of pressurization, what is meant by ‘raise or lower the cabin’? How do you accomplish this?
To ‘raise’ the cabin is to increase the cabin altitude and ‘lower’ the cabin is to decrease the cabin altitude. In normal operation pressurization is almost totally automatic and the crew only has to set the landing
field elevation. In simple terms pressurization works by pressurized air from engine or APU bleed, regulated through the packs, enters into the cabin. The two outflow valves mounted on the rear pressure bulkhead regulate the amount of air leaked overboard. By varying the difference of how much air comes into the cabin and how much goes out, the pressure of the air in the cabin is regulated up to a maximum differential pressure between inside and outside the pressure vessel, the cabin, to 8.7 psi. Standard sea level pressure is 14.7 psi. which is the weight of a 1 inch square column of air. As altitude increases the weight at that point in the column decreases due to the higher you go the less air there is above you and therefore the lower the pressure. The decrease is not directly proportional with altitude gain. 10,000 feet is the highest altitude considered safe for prolonged normal human existence without supplemental O2. The goal of pressurization is to keep the cabin at a pressure level corresponding to an altitude lower than 8000 feet. Whether auto or manually, setting the pressurization is simply adjusting the pressure inside the cabin to 10 correspond to the pressure at some altitude along the column of air. If you decrease the pressure in the cabin you increase the cabin altitude. If you increase the pressure, you decrease the cabin altitude. With normal system operation all that is required of the crew is to set the landing field elevation. The Manual Pressurization Control {procedure is in the QRH Abnormal 2-6. Review it and understand what is physically taking place with each step.
What does the LDG ELEV knob on the pressurization control panel do?
Sets the landing elevation on the status page
What happens when EMER DEPR switchlight is pressed in (on)?
Pressing the EMER DEPR switchlight causes the Cabin Pressure Controller to drive the outflow valves fully open, climbing the cabin to 14,250+/- 750 feet
At flight level 330 for some reason you press the Ram Air Ventilation switchlight in. What will happen?
Nothing, if the Packs are on. A Check valve prevents the depressurization.
What does pressing the PRESS CONTROL switchlight twice do?
Switches Pressure Controllers
Flying at FL 200, the EMER DEPRESS switch/light is pressed, what pressure altitude should the cabin reach?
14,250 ± 750 feet
Where is the unpressurized takeoff procedure found?
QRH
Where is the unpressurized landing procedure found?
QRH
When might you be required to perform an unpressurized
takeoff?
APU deferred and either the airport analysis requires bleeds closed or the anti-ice is being used for takeoff.
When no bleed is provided or electrical power is lost, what happens to the 10th stage SOVs?
The 10th stage bleed air system uses a common manifold that can receive bleed air from either the engines, APU or an external high pressure source. The 10th stage manifold is located in the aft equipment bay. An isolation valve divides the left and right sides of the manifold, which are connected through a crossover duct. When the isolation valve is open, any source of bleed air can pressurize the entire manifold. With the isolation valve closed each engine pressurizes its respective side of the manifold. Located in the equipment bay, the 10th stage bleed air SOVs are electrically controlled and pneumatically operated. When no bleed air is provided or electrical power is lost, the 10th stage SOVs are spring-loaded to close.
What is the purpose of the one way check valve at the 10th stage engine bleed tap?
As long as the respective engine is operating, pressing either 10th stage (L or R) SOV switch in on the BLEED AIR control panel will open the SOV. One-way check valves are provided in the 10th stage ducts by the engine bleed tap. The check valves permit high pressure airflow from the engine compressor to the manifold, but prohibit the reverse flow of manifold air into the engine. Similar valves are provided for the APU and external ground air connections.
What is CPAM? What does CPAM do? What happens if CPAM fails?
The CPAM provides pressurization data for the EICAS display. The EICAS indications provided by CPAM are:
* cabin altitude C ALT
* cabin rate of climb RATE
* differential pressure ΔP
When the cabin altitude reaches 8,500 ft., the CPAM generates a CABIN ALT caution message. If the cabin were to exceed 10,000 ft. or greater, a CABIN ALT warning message along with a ’CABIN PRESSURE’ aural is provided. The CPAM also illuminates the NO SMOKING/FASTEN SEAT BELT signs if in AUTO. At 14,000 ft. the passenger oxygen masks autos deploy. In case of CPAM failure, the redundant CPC generates the EICAS messages, but the auto drop-down passenger mask function, along with the auto SEAT BELT/NO SMOKING function are lost.
Under what conditions might you have to perform an unpressurized landing?
APU deferred and either the airport analysis requires bleeds closed or the anti-ice is being used for landing
If you are doing an unpressurized landing in the CR2, APU inoperative, in icing conditions, on a contaminated runway. What bleed source supplies wing and cowl anti-ice? What bleed source supplies the thrust reversers? Is it capable of supplying both simultaneously?
14th stage engine bleed is the source for wing & cowl anti-ice as well as thrust reversers. In the landing configuration or on the ground, the anti-ice systems are disabled to redirect all 14th stage air to the PDU.
