Pressurization Control & Operation - Pneumatics - Airframes & Aircraft Systems #42
Summary
TLDRThis lesson explores different types of pressurization controllers in aircraft, focusing on their evolution from pneumatic to electronic systems. It discusses the controller's functions, including cabin altitude control, rate of change, and maximum differential pressure limitation. The script explains how modern aircraft use electronic controllers for automatic pressurization, with pilots setting cruise and landing altitudes. It also covers manual control and the necessary instruments for monitoring cabin pressure, altitude, and differential pressure, ensuring passenger comfort and safety.
Takeaways
- 😀 Pressurization systems use various types of controllers, including pneumatic, electropneumatic, and electronic controllers.
- 🛫 Controllers manage cabin altitude, rate of change, and limit maximum differential pressure to ensure passenger comfort and aircraft integrity.
- 🔑 Older generation jets use electropneumatic controllers, while modern aircraft rely on electronic controllers for pressurization.
- ✈️ On Boeing 737 aircraft, pilots set cruise altitude and landing airfield elevation during pre-flight preparation, which the controller uses to manage cabin pressure.
- 🚀 Airbus types typically operate without pilot input, with the controller receiving altitude data from flight management computers.
- 📊 The pressurization control system in modern aircraft includes automatic controllers with inputs from static pressure sensing systems and cabin pressure sensors.
- 🔄 In case of a controller failure, a standby controller automatically takes over to ensure continued pressurization.
- 📉 The minimum required indications for pressurization systems are cabin altitude, vertical speed, and differential pressure, displayed on gauges or LCD screens.
- 🔧 In manual mode, pilots can control the outflow valve position to directly manage cabin pressure, altitude, and rate of climb or descent.
- ⚠️ Cabin pressurization rates should be carefully monitored, with typical limits of 500 feet per minute climb and 300 feet per minute descent to prevent discomfort.
Q & A
What are the main types of controllers used in pressurization systems?
-Pressurization systems use various types of controllers including purely pneumatic for small aircraft, electropneumatic for older generation jets, and electronically operated for most modern aircraft.
What are the three primary functions of a pressurization controller?
-A pressurization controller controls the cabin altitude, the rate of change of cabin altitude, and limits the maximum differential pressure.
How does an old generation controller differ from a modern electronic controller in terms of pilot interaction?
-Old generation controllers require the pilot to manually select the desired cabin altitude and rate of change, while modern electronic controllers automate these tasks based on received altitude data and an inbuilt program.
What specific actions does the pressurization controller take during the aircraft's pre-flight preparation on a Boeing 737?
-On a Boeing 737, the pilot selects the aircraft's cruise altitude and landing airfield elevation during pre-flight preparation, and the controller automatically manages the outflow valve to achieve and maintain the appropriate cabin altitude.
How does the pressurization control system in an Airbus aircraft differ from that in a Boeing 737 during normal operation?
-In most Airbus types, the pilot makes no inputs to the pressurization system during normal operation as the controller receives all necessary altitude data from the flight management computers.
What are the minimum indications required for a pressurization system?
-The minimum indications required for a pressurization system are cabin altitude, cabin vertical speed, and cabin differential pressure.
What is the purpose of pre-pressurization in aircraft before takeoff?
-Pre-pressurization ensures a gradual transition to pressurized flight and prevents surges of pressure on rotation during takeoff.
How does the pressurization controller adjust the cabin pressure during the aircraft's climb and descent?
-The controller adjusts the cabin pressure by controlling the rate of cabin climb or descent in proportion to the aircraft's climb or descent rate, maintaining a slightly less than the maximum permitted differential pressure.
What happens when the aircraft reaches its cruise altitude in terms of cabin pressurization?
-When the aircraft reaches its cruise altitude, the controller maintains a constant cabin altitude, resulting in a constant mass flow of air through the cabin with the mass of air coming in from the packs equaling the mass leaving through the outflow valve.
How does the pressurization system handle significant changes in the aircraft's altitude during level flight?
-In level flight, small changes in aircraft altitude are accommodated without any change in cabin pressure. However, if a significant increase in crew's altitude is required, the flight altitude selection must be reset to prevent exceeding the maximum differential pressure.
What are the normal cabin descent rates during the aircraft's descent and landing?
-The normal cabin descent rate during the aircraft's descent is about 300 feet per minute, and it is adjusted to approximately 0.1 psi on touchdown.
Outlines
🛫 Pressurization Controllers and Systems
This paragraph introduces the topic of pressurization controllers used in aircraft. It explains the different types of controllers, from pneumatic in small aircraft to electronically operated in modern planes. The paragraph discusses the functions of a controller, which include controlling cabin altitude, rate of change, and limiting maximum differential pressure. It also touches on how older generation controllers work with electric motor-driven outflow valves, while modern aircraft use electronic controllers that automatically adjust based on aircraft and cabin altitude signals. The paragraph concludes with a mention of the Boeing 737 and Airbus types, where the controller settings are either pre-set by the pilot or managed entirely by the flight management system.
🔧 Pressurization Control Panel and Modes
Paragraph 2 delves into the specifics of the pressurization control panel and its operation. It describes the panel's location and the rotary knobs used by pilots to set cruise altitude and landing airport elevation. The paragraph outlines the three modes of operation: auto, alternate, and manual. In auto mode, one of the automatic controllers manages the pressurization, while alternate allows the pilot to switch to the other controller. Manual mode gives the pilot direct control over the outflow valves. The paragraph also details a typical flight's pressurization process, from pre-flight settings to takeoff, climb, cruise, and descent, emphasizing the controller's role in managing cabin pressure and rate of climb or descent according to the aircraft's flight phase.
✈️ Manual Control and Cabin Pressure Monitoring
The final paragraph focuses on manual control of the pressurization system and the importance of monitoring cabin pressure. It explains how the pilot can adjust the outflow valve position to control cabin altitude, rate of climb or descent, and differential pressure. The paragraph provides guidance on how to interpret the placard showing cabin altitude against aircraft altitude and how to manage the outflow valve to achieve the desired cabin conditions. It also discusses the recommended rates of climb and descent to ensure passenger comfort and safety. The paragraph concludes with a reminder of the consequences of reaching certain cabin altitudes and differential pressures, including warnings and the activation of relief valves.
Mindmap
Keywords
💡Pressurization systems
💡Controllers
💡Cabin altitude
💡Differential pressure
💡Outflow valves
💡Flight profile
💡Auto mode
💡Manual mode
💡Pre-pressurization
💡Cabin vertical speed
💡Flight management computers
Highlights
Examination of various types of controllers used by pressurization systems.
Analysis of required pilot inputs for pressurization systems.
Discussion on indicating systems for crew information on system operation.
Overview of a typical flight profile using an automatic pressure controller.
Demonstration of manual pressurization control by the pilot.
Description of pressurization controllers varying from pneumatic to electronic operation.
Explanation of the three functions of a controller: controlling cabin altitude, rate of change, and limiting maximum differential pressure.
Details on old generation controllers with manual cabin altitude and rate of change selection.
Modern aircraft's automatic control by electronic controllers based on aircraft and cabin altitude signals.
Boeing 737's automatic control of outflow valves based on pilot-selected cruise and landing altitude.
Airbus types' pressurization control that operates without pilot input, relying on flight management computers.
Schematic diagram explanation of a modern passenger transport aircraft's pressurization control system.
Duplication of automatic controllers with inputs from various aircraft systems for redundancy.
Description of the cabin pressurization control panel's location and functionality.
Minimum indications required for a pressurization system: cabin altitude, vertical speed, and differential pressure.
Functionality of the cabin altimeter, vertical speed indicator, and differential pressure gauge.
Procedure in case of pressure controller or outflow valve malfunction, indicated by high pressure readings.
Operation of pressurization system in auto mode during pre-flight, takeoff, and climb.
How the controller maintains cabin altitude during level flight and adjusts for changes in aircraft altitude.
Manual control of the pressurization system, including outflow valve position adjustment.
Guidance on cabin rates of climb and descent to ensure passenger comfort.
Summary of the lesson on understanding the relationship between cabin pressure, cabin altitude, and ambient pressure.
Transcripts
in this lesson we will examine the
various types of controllers used by
pressurization systems
we will look at the required pilot
inputs and at the indicating systems
used to inform the crew
of correct system operation we will look
at a typical flight profile
using an automatic pressure controller
and finally
we will see how the pilot can control
the pressurization manually
pressurization controllers vary in
construction and operation
on simpler small aircraft they may be
purely pneumatic in their operation
on old generation jets they are
electropneumatic
and in the case of most modern aircraft
they are electronically operated
whatever type of controller is used it
will receive signals
informing it of both the cabin and
ambient pressures
the controller has three functions it
will control the cabin altitude
it will control the cabin altitude rate
of change and it would limit the maximum
differential pressure
old generation controllers have controls
for selecting the required cabin
altitude
and cabin altitude rate of change they
send signals
to the electric motor-driven outflow
valves
on modern aircraft most of the control
is done automatically
by an electronic controller
the controller receives electrical
signals proportional to aircraft
altitude
and cabin altitude it will then control
the outflow valves
to maintain a cabin altitude according
to an inbuilt program
on the boeing 737 the pilot selects the
aircraft cruise altitude
and landing airfield elevation during
his pre-flight preparation
the controller automatically controls
the outflow valve to achieve and
maintain
the appropriate cabin altitude for the
phase of flight
on most airbus types during normal
operation
the pilot makes no inputs to the system
at all
the controller receives all necessary
altitude data from the flight management
computers
this schematic diagram shows the
arrangement of the pressurization
control system
of a modern passenger transport aircraft
the automatic controllers are duplicated
and have inputs from the aircraft static
pressure sensing system
the cabin pressure sensors and the air
ground logic system
if pre-pressurization that is
pressurization on the ground prior to
takeoff
is part of the schedule then inputs are
also required
from the thrust lever positions
one controller is operating and the
other is on standby
the rolls are automatically reversed
after each landing
in the event of a failure the standby
controller will automatically take over
control
the controllers are normally located
away from the flight deck
in an electrical service center
each outflow valve is operated by one of
three electric motors
there is one motor for each automatic
controller and another for manual
control
the minimum indications required for a
pressurization system
are cabin altitude
cabin vertical speed
and cabin differential pressure
this information can either be presented
on direct reading gauges
or electronically on an lcd screen
the cabin altimeter measures cabin
pressure
but it is expressed on the gauge in
terms of the equivalent pressure
altitude of the cabin
the cabin vertical speed indicator vsi
indicates the rate at which the aircraft
cabin is climbing or descending
the cabin differential pressure gauge
indicates the difference between the air
pressure inside the cabin
and the outside air pressure and is
generally calibrated
in pounds per square inch
in the event of a malfunction of the
pressure controller or outflow valve
a high pressure reading on this
instrument would indicate that the
safety valves
were controlling the cabin pressure at
the structural maximum pressure
differential
the cabin pressurization control panel
is remote from the pressurization
controller
and will generally be fitted in the
overhead panel on the flight deck
the control panel may have rotary knobs
for the pilot to set the expected cruise
altitude
and the elevation of the landing airport
in a typical system there are three
modes of operation
auto alternate and manual
in auto mode one of the two automatic
pressurization controllers will be
operating
the pilot can force the system to use
the other controller by selecting
alternate
selection of manual will lock out all
normal automatic functions
and enable the pilot to control the
position of the outflow valves
we will now take a look at a typical
flight to see how a typical
pressurization system will operate in
the auto mode
during his pre-flight preparation the
pilot will set the expected cruise
altitude
and the landing airfield elevation in
our example
the aircraft will be cruising at thirty
thousand feet
before landing at an airfield with a
pressure altitude of 1000 feet
with the aircraft on the ground the
operating controller will hold the
outflow valve fully open
when the pilot opens the thrust levers
for takeoff
the controller will signal the outflow
valve to move towards closed
pre-pressurizing the aircraft cabin into
a small differential pressure
of approximately 0.1 psi
this ensures that the transition to
pressurized flight will be gradual
and that there will be no surges of
pressure on rotation
as the aircraft takes off the ground air
logic system will signal the controller
to switch to proportional control
the controller will sense ambient and
cabin pressure and position the outflow
valves to control the rate of cabin
pressure reduction
or cabin climb in proportion to the rate
of climb of the aircraft
so that slightly less than the maximum
permitted differential pressure is
attained
as the aircraft reaches its cruising
altitude
the cabin rate of climb will normally be
between
300 and 500 feet per minute with a
maximum limit
of 500 feet per minute
if the aircraft is required to level off
during the climb then the pressurization
controller will sense this
and level off the cabin
when the aircraft begins to climb again
the controller will once more position
the outflow valves to control the rate
of change of cabin altitude
in proportion to the rate of climb of
the aircraft
the cabin rate of climb will again
normally be between
300 and 500 feet per minute
when crew's altitude is reached the
controller will maintain a constant
cabin altitude
there will now be a constant mass flow
of air through the cabin
the mass of air coming in from the packs
will equal the mass leaving through the
outflow
valve once established in the cruise
small changes in aircraft altitude will
be accommodated without any change in
cabin pressure
however if the crew's altitude has to be
increased significantly
then the flight altitude selection will
have to be reset
if this is not done and the maximum
differential pressure is reached
the controller will not allow further
increase in differential pressure
and the aircraft will now be a maximum
differential control
as the aircraft climbs the cabin will
also climb
to keep the differential pressure within
limits
when the controller senses that the
aircraft is descending
it will switch back to proportional
control and descend the cabin at a rate
to produce a differential pressure
of approximately 0.1 psi on touchdown
the descent rate will normally be about
300 feet per minute
when the aircraft lands and the ground
air logic system switches to ground mode
the outflow valves will slowly open
fully to equalize cabin and ambient
pressures
on older types of aircraft the cabin is
not pressurized prior to takeoff
and because the fuselage is not designed
to absorb the landing shock
simultaneously with pressure
differential forces
the cabin is completely depressurized
just prior to landing
with the system under manual control the
outflow valve position can be adjusted
by operation of the manual open close
switch
the pilot now controls the differential
pressure cabin altitude
and cabin rate of climb or descent
on the system shown here a placard along
the bottom of the control panel
shows cabin altitude against aircraft
altitude
at maximum differential pressure the
pilot can consult this
in order to establish the cabin altitude
required for any given aircraft altitude
opening the outflow valve will cause the
differential pressure to decrease
the cabin pressure to decrease and the
cabin altitude to increase
the cabin vsi will show a climb
closing the outflow valve will cause the
differential pressure to increase
the cabin pressure to increase and the
cabin altitude
to decrease the cabin vsi
will show a descent
cabin rates of climb and descent should
be carefully monitored
and should not normally be allowed to
exceed 500 feet per minute during the
climb
or 300 feet per minute in the descent in
order not to cause too much discomfort
for the passengers
that is the end of the lesson you should
now understand the relationship between
cabin pressure
cabin altitude and ambient pressure
remember in level flight if the outflow
valve is opening
the cabin vertical speed indicator will
show a rate of climb
the cabin altitude will increase and the
differential pressure will decrease
if the cabin altitude reaches 10 000
feet then an oral
and or visual warning will be given to
the crew
similarly in level flight if the outflow
valve is closing
the cabin vsi will show a rate of
descent the cabin altitude will decrease
and the differential pressure will
increase if the maximum differential
pressure is exceeded
then the positive pressure relief valves
will open
finally remember that if the
pressurization system is in the manual
mode
the cabin altitude the cabin rate of
change
and the differential pressure are all
controlled by the pilot
operating an outflow valve manual open
close switch
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