Pressurization Control & Operation - Pneumatics - Airframes & Aircraft Systems #42

Summary

This 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

00:00

🛫 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.

05:01

🔧 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.

10:01

✈️ 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.

Keywords

💡Pressurization systems

Pressurization systems are integral to modern aircraft, ensuring a comfortable and safe environment for passengers and crew at high altitudes. These systems regulate the air pressure inside the aircraft cabin to mimic conditions at lower altitudes. In the script, various types of controllers used by pressurization systems are examined, highlighting their importance in controlling cabin altitude, rate of change, and maximum differential pressure.

💡Controllers

Controllers in the context of aircraft pressurization refer to the mechanisms that manage the flow of air into and out of the cabin to maintain a safe and comfortable pressure. The script discusses different types of controllers, from pneumatic to electropneumatic and electronic, which receive signals about cabin and ambient pressures to control the pressurization process.

💡Cabin altitude

Cabin altitude is the pressure altitude that the aircraft's pressurized cabin is set to simulate. It is a crucial parameter in pressurization systems as it affects the comfort and health of passengers and crew. The script explains how controllers manage cabin altitude, ensuring it changes at a safe rate and does not exceed maximum differential pressure limits.

💡Differential pressure

Differential pressure is the difference between the internal cabin pressure and the external atmospheric pressure. It is a critical safety parameter in aircraft design, as excessive differential pressure can compromise the structural integrity of the aircraft. The script outlines how controllers limit the maximum differential pressure to ensure the aircraft's safety.

💡Outflow valves

Outflow valves are components of the pressurization system that regulate the amount of air leaving the cabin, thus controlling the cabin pressure. The script mentions that on modern aircraft, these valves are controlled by electric motors, which receive signals from the electronic controller to maintain the desired cabin pressure.

💡Flight profile

A flight profile refers to the planned altitude and speed of an aircraft throughout a flight. The script discusses how an automatic pressure controller uses the flight profile, including cruise altitude and landing airfield elevation, to manage the pressurization process automatically.

💡Auto mode

Auto mode in pressurization systems refers to the automatic operation of the system where the controller manages the cabin pressure without direct pilot input. The script provides an example of how, in auto mode, the controller adjusts the outflow valves based on the aircraft's altitude and rate of climb to maintain a comfortable cabin environment.

💡Manual mode

Manual mode allows the pilot to override the automatic pressurization system and control the outflow valves directly. This mode is used when the automatic system fails or during specific flight conditions that require manual intervention. The script explains that in manual mode, the pilot is responsible for adjusting the cabin altitude, rate of change, and differential pressure.

💡Pre-pressurization

Pre-pressurization is the process of pressurizing the aircraft cabin while on the ground before takeoff. The script mentions that for aircraft that perform pre-pressurization, inputs from thrust lever positions are required to ensure a smooth transition to pressurized flight.

💡Cabin vertical speed

Cabin vertical speed, also known as cabin rate of climb or descent, is the rate at which the cabin altitude changes. It is an important parameter for passenger comfort and safety. The script describes how the pressurization controller adjusts the outflow valves to maintain a cabin vertical speed within a safe range, typically between 300 and 500 feet per minute during climb.

💡Flight management computers

Flight management computers are systems that control various aspects of an aircraft's flight, including navigation and systems management. In the context of pressurization, as mentioned in the script, these computers provide altitude data to the pressurization controller, enabling automatic management of cabin pressure in modern aircraft.

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