ECS

Question 1

Outflow, Safety and Ground Safety Valves

Answer 1

An electrical outflow valve is located on the aft pressure bulkhead. The valve mechanism is activated by a triple-motored actuator. Two inputs are from the CPCs and the third is a manual input. Two safety valves are installed. A ground safety valve is installed to ensure the aircraft remains depressurized while on the ground.

Question 2

Cabin Pressure Controllers (CPC)

Answer 2

Two CPCs control all automatic phases of pressurization. Only one controller is active at any time, the other controller operates as the standby. When the active controller fails, the standby controller automatically assumes the active role. The active controller is identified on the ECS synoptic page.

Question 3

CABIN PRESS Control Panel

Answer 3

The CABIN PRESS control panel provides the pilot with the switches needed to operate the system in both automatic and manual mode. In addition, the control panel contains a temperature corrected altitude sensor and microprocessor. The microprocessor performs CPAM-type (Cabin Pressure Acquisition Monitor) functions and provides a third level of automatic control.

Question 4

The CONTROL PANEL MICROPROCESSOR is solely responsible for the following functions:

Answer 4

• controls the automatic drop down of the passenger oxygen masks at 14,000 foot cabin altitude
• provides the instruction to limit cabin altitude to 14,500 ± 500 feet
• controls the opening and closing speed of the ground valve during ground sequences to avoid any perturbation of the outflow valve

Question 5

CABIN ALT caution message and ‘Cabin Pressure’ aural

On the primary page, the control panel microprocessor and active pressure controller provides these messages

Answer 5

cabin altitude greater than or equal to 8500 ft.

Question 6

CABIN ALT warning message

On the primary page, the control panel microprocessor and active pressure controller provides these messages

Answer 6

cabin altitude cabin altitude greater than or equal to 10000 ft

Question 7

DIFF PRESS warning message

On the primary page, the control panel microprocessor and active pressure controller provides these messages

Answer 7

differential pressure greater than or equal to 8.6 PSID

Question 8

At 10000 ft. CABIN ALTITUDE, both the active controller and control panel microprocessor will illuminate the

Answer 8

NO SMOKING/ FASTEN SEAT BELT signs if the switches are selected to AUTO.

Question 9

With a failure of the CPCP, what will not occur?

Answer 9

automatic drop down of the passenger oxygen and illumination of the seat belt and no smoking signs will not occur.

Question 10

The purpose of the Outflow Valve

Answer 10

The electrical outflow valve is located on the aft pressure bulkhead and controls the discharge rate of air from the aircraft.

The outflow valve mechanism is activated by a triple-motored actuator. The DC motors are associated with one of three operating channels. Each CPC controls its own DC motor on the actuator to modulate the outflow valve. The third DC motor is used during manual pressurization. In automatic mode, the active CPC maintains the aircraft pressurization schedule by electrically modulating the outflow valve to control the discharge rate.
In manual mode, the outflow valve is controlled electrically by switches on the CABIN PRESS panel. From the control panel, the pilot can command the system to hold a cabin altitude or manually control the rate at which the cabin pressure climbs or descends.

Page 7-20 in the Mesa systems book

Question 11

The purpose of the Safety Valves?

Answer 11

The safety valves are located on the aft pressure bulkhead and provide over-pressure and negative pressure relief.
The valves are pneumatically operated and spring-loaded closed. When the cabin differential pressure exceeds normal limits, the safety valves open to relieve the excessive pressure.
Should a negative pressure condition develop, (ambient pressure is greater than cabin pressure), the safety valves open to equalize the pressure.
Pg 7-21

Question 12

Purpose of the Ground Valve

()=important shit

Answer 12

(The ground valve is used to ensure that the aircraft is depressurize when on the ramp and to dump overboard the air used in ventilating the CRTs and avionics bay’s electronic equipment.)
The control panel microprocessor using proximity sensing system data (WOW and door switches) from the active pressure controller, controls the opening and closing of the valve. The opening and closure speed of the valve is controlled to prevent pressure bumps in the system.
On the ramp, the ground valve is fully open. When the passenger and galley doors are closed, the valve is motored closed. If the valve fails to close, the amber OVBD COOL caution message is displayed. The valve to be manually closed for flight to improve dispatch reliability.

(After touchdown, the ground valve opens. The valve takes approximately 60 seconds to open. If the valve fails to open, the OVBD COOL FAIL status message is displayed.)

(If EMER DEPRESS is selected while the aircraft is on the ground, the valve will open at full speed (2 sec).)

Question 13

Automatic pressurization modes

The automatic modes of the active controller include the following:

Answer 13

• ground mode
  • pre-pressurization mode

* takeoff abort mode
• climb mode
• flight abort mode
• cruise mode
• descent mode
• landing mode

Question 14

Automatic pressurization modes

Ground Mode

Answer 14

The ground mode drives the outflow and ground valves fully open to provide maximum ventilation on the ground. When the passenger and galley service doors are closed the ground valve is closed.

Question 15

Automatic pressurization modes

Pre-pressurization mode

Answer 15

The pre-pressurization mode is activated when the thrust levers are advanced for takeoff when the aircraft is on the ground. Pre-pressurizing the aircraft allows the outflow valve to achieve a controlling position prior to takeoff to eliminate any noticeable pressure bumps. The cabin is pressurized to –150 feet below the actual field elevation.

(When conducting a NO BLEED takeoff, the outflow and ground valves are closed.)

Question 16

Automatic pressurization modes

Take-off Abort Mode

Answer 16

The takeoff abort mode is entered when the thrust levers are retarded during a rejected takeoff. The cabin altitude is rated back to field elevation at 500 feet/min for twenty seconds then the outflows are driven full open. The ground mode is then re-established.

Question 17

Automatic pressurization modes

Flight Abort Mode

Answer 17

The active CPC will attempt to maintain the pre-pressurization altitude during the first 10 minutes of flight. This mode alleviates the pilot having to reset the landing elevation when aborting a flight to return to the takeoff airfield.

Question 18

Recirculation Fans

Answer 18

(Recirculation fans are utilized to remove air from the cabin. )Cabin exhaust air is reused or discharged into the underfloor area. A RECIRC ON/OFF switch is located on the air conditioning panel.

Question 19

Automatic pressurization modes

Climb Mode

Answer 19

Cabin pressurization is programmed according to selected landing elevation and a theoretical schedule of cabin altitude versus aircraft altitude. The cabin climb profile varies directly with the aircraft’s rate of climb. A typical cabin climb rate is approximately 300-500 fpm.

Question 20

Automatic pressurization modes

Cruise mode

Answer 20

For every cruising altitude, there is an assigned cabin altitude. When cruising altitude is reached, the descent mode is armed.

Question 21

Automatic pressurization modes

Descent mode

Answer 21

The rate of cabin decent is directly related to the aircraft’s rate of descent. In the case of a high-speed descent, the rate of cabin descent is increased according to the calculation of remaining flight time. The remaining flight time is calculated from the aircraft speed received from the ADC. A typical cabin descent rate is approximately 300 fpm.
For example, if the A/C’s descent rate is 2000 fpm the cabin will descend at approximately 300 fpm. If the A/C is descending at > 5000 fpm the cabin will descend at 750 fpm.
Cabin altitude will descend on schedule until the cabin altitude is approximately –150 feet below the selected landing destination elevation.

Question 22

Automatic pressurization modes

Landing modes

Answer 22

The landing mode is entered when the active controller receives a weight on wheels signal from the PSEU and one of the thrust levers is at idle. After touchdown, the cabin altitude is increased to the landing elevation, and then the outflow valve and ground valves are fully opened.

Question 23

Manual Pressurization Control

Answer 23

When MAN is selected on the CABIN PRESS control panel the outflow valve is manually controlled. The MAN ALT lever and the RATE knob on the CABIN PRESS control panel are used to position the outflow valve. An UP selection on the MAN ALT selector will cause an increase in cabin altitude at the rate selected on the RATE control knob. A DN selection of the MAN ALT selector will cause the cabin altitude to decrease at the rate set by the MAN RATE control knob. When the RATE knob is selected to HOLD, the cabin altitude will be maintained regardless of changes to the aircraft altitude.
When manual pressurization is selected, pressurization data is reproduced on the EICAS primary page.

Pg 7-25

Question 24

Emergency Depressurization Control

Answer 24

Selecting emergency depressurization overrides both automatic and manually control of the system. When the EMER DEPR switchlight is pressed, the MANUAL DC motor will drive the outflow valve fully open. Cabin altitude is measured by the altitude sensor inside the control panel.
The control panel microprocessor restricts the cabin altitude to a maximum of 14,500 ± 500 feet. If aircraft altitude is below 14,500 ± 500 feet, the aircraft will depressurize.
If the CPAM fails, the standby CPC will generate the EICAS messages.

When selected in the On position, indicates both outflow valves are commanded open.

Question 25

Ram Air Button

Answer 25

Allows air from the Ram Air Scoop to enter the Air Conditioning duct.

Question 26

Recirculation fans

Answer 26

Activates both re circulation fans, and allows recirc to be mixed with Conditioned Air for delivery to the flight deck and passenger cabin

Question 27

Cargo switch

Answer 27

CARGO: Controls air circulation in the cargo bay.

OFF: intake and exhaust SOVs are closed to seal aft cargo bay enclosure.

AIR: SOVs opened, recirculated or conditioned air, ventilates aft cargo bay.

COND AIR: SOVs opened, recirculated or conditioned air, ventilates aft cargo bay. Electric heater maintains bay temperature.

Question 28

Rheostat knobs

Answer 28

Adjust the respective compartment temperature in automatic mode.

Question 29

Differential Pressurization Schedule

Answer 29

Normal max operating: 8.4 psid
Max Differential: 8.6 psid
Negative Pressure Relief: -0.5

Question 30

Air Conditioning System Controller (ACSC)

Answer 30

Two dual channel controllers (ACSC) monitor and control the air conditioning systems. Each controller in itself is divided into two fully redundant channels; A and B. Only one channel of each controller is active at any time and controls the Air Conditioning System and Bleed System for their applicable side. The other channel maintains a monitoring/standby mode. ACSC 1 monitors the left pack; ACSC 2 controls the right pack.

Question 31

Air Conditioning Packs

Answer 31

The packs provide conditioned air for the fuselage compartments by decreasing the temperature and water content of the bleed air used in the conditioning process.

Question 32

Pack Valves

Answer 32

Flow control valves referred to as the Pack Valves, are used to control the mass airflow through the packs. The pack valves are electrically controlled, pneumatically operated, modulating shut-off valves. Selecting the associated PACK switchlight on the AIR-CONDITIONING panel operates the pack valves.

The pack valves are automatically closed when the engine START switchlight is pressed. Shutting down the air conditioning systems (if running), insures that the air turbine starters receive sufficient airflow for starter operation. When the start valve closes, the packs return to their previous selection.

Question 33

Temperature Control

Answer 33

When cold air is requested, three heat exchangers and an air cycle machine (ACM) are used to cool the temperature of the bleed air. A pre- cooler lowers the temperature of the bleed air prior to entering the pack. From the precooler, the air is cooled again by the primary heat exchanger and then is sent to the ACM compressor where the pressure and temperature of the air is increase significantly. From the compressor, the air is passed through the secondary heat exchanger where it experiences a third level of cooling.
From the main heat exchanger, the air is directed to the water extraction loop. The high-pressure water extraction loop consists of a re-heater, condenser and water extractor. Using simple air to air heat extraction principles, the re-heater and condenser cools the air to promote condensation of the water vapor in the bleed air. The water extractor removes the water and sprays it into the ram air duct. Adding moisture to the ram air improves the cooling efficiency of the three heat exchangers.
From the water extractor, the air is sent back to the re-heater where one additional function is performed. The air is re-heated prior to re-entering the ACM to improve the efficiency of the heat extraction turbine.
The temperature control valve allows hot bleed air to bypass the cooling and water extraction sections of the pack. By blending air from the bypass duct with air from the pack, the desired temperature can be achieved.
The ACSC provides anti-ice protection for the pack. When ice is detected in the water extraction loop, the discharge temperature of the pack is increased by opening the temperature control valve. Opening the valve melts the ice in the condenser and prevents additional ice from forming in the water extraction loop.

Question 34

Automatic Temperature Control Mode

Answer 34

The ACSC controls the mixing of cold air from the ACM and hot air from the bypass duct by regulating the position of the temperature control valve. Temperature control valve regulation is a function of the temperature selected at the AIR CONDITIONING panel and the actual temperature as measured by the temperature sensor in the compartment. Flight deck temperature is monitored by one sensor. Two sensors monitor the temperature in the passenger cabin, one sensor is in the forward cabin, the other in the aft.
On the ground, when the ACSC detects a temperature difference greater than 10°C between the selected and actual compartment temperature, a Pull-Up or Pull-Down sequence is initiated. The sequence shift the pack to high airflow and changes the pack’s operating temperature limits to ensure maximum cooling or heating capability.

Question 35

Manual Temperature Control Mode

Answer 35

Manual control of the flight deck or passenger cabin temperature is accomplished at the AIR-CONDITIONING control panel. In manual mode, the pilot controls the airflow through the pack by direct actuation of the temperature control valve. The pack discharge temperature can be increased or decrease by means of the HOT-COLD toggle switch. The pack discharge temperature is displayed on the status page and ECS synoptic page. The pack discharge temperature is monitored by the DCU. If the discharge temperature is not within the range of 5 to 85°C, the pack discharge temperature is displayed as amber on EICAS.

Question 36

Over-Temperature Protection

Answer 36

The temperature of the airflow is monitored by sensors at various locations inside the pack. When an over-temperature condition is detected, the ACSC automatically closes the pack valve; the pack shuts down and the amber L or R HI TEMP caution message is displayed.

Question 37

What is the Temperature range when in Manual Mode?

Answer 37

5 to 85 Celsius.

Anything above or below, the pack discharge temperature is displayed as Amber on the EICAS.

Question 38

The pack can be restarted only when the following conditions are met:

Answer 38

• high pack temperature disappears (automatic)
• pack is manually selected OFF at the AIR-CONDITIONING panel.

Question 39

Ram Air Scoop

Answer 39

(Ram air, taken from the air scoop at the base of the vertical fin, is used as the cooling medium for the air to air heat exchangers.) Ram air passes through the secondary, primary and pre-cooler heat exchangers to extract heat from the bleed air used by the air conditioning systems. The ram air after passing through the heat exchangers is discharged through exhaust vents on the lower left and right sides of the aft fuselage. On the ground, the airflow through the ram air scoop is inadequate for cooling of the heat exchangers. A fan, mechanically driven by the air cycle machine is installed in the ram air duct to increase the airflow through the duct for cooling of the heat exchangers.

Question 40

Ram Air Valve

Answer 40

If both air conditioning systems fail, ram air can be used to ventilate the flight deck and passenger cabin at low altitude. Selecting the guarded RAM AIR switchlight to open allows air from the ram air scoop to enter the mixing manifold.

Question 41

Air distribution and re circulation

Answer 41

Air Distribution
Conditioned air from the air conditioning packages is blended with filtered re-circulated air from the passenger cabin to optimize ECS performance. The blending of conditioned and re-circulated air occurs inside the mixing manifold.
The mixing manifold allows mixing of the re-circulated and conditioned air while segregating the output of the left pack from that of the right pack. The left pack supplies the flight deck; the right pack supplies the passenger cabin. Should either pack fail, the mixing manifold allows the operable pack to supply conditioned air to both the flight deck and passenger cabin.

Re-circulated Air
After conditioning the cabin, the air is removed from the cabin by dado panels located at floor level on the left and right sides of the cabin. The dado panels are connected to exhaust ducts. Each exhaust duct contains a re-circulation fan. The exhaust air is filtered and returned to the mixing manifold for blending with the conditioned air. During ECS operation, the re-circulation air ratio can be as high as 34% of the total airflow. The RECIRC FAN switch on the AIR-CONDITIONING panel energizes the re- circulation fans. The system is monitored by the ACSC.

Flight Deck Distribution
The mixing manifold provides left pack/re-circulated air through a duct to the flight deck gaspers, vents and side console outlets. The air is also used as a backup source of cooling for the EICAS and EFIS displays.

Passenger Cabin Distribution
From the mixing manifold, three ducts direct right pack/re-circulated air to the passenger cabin, galleys and lavatory(s). The forward duct supplies the front and mid sections of the cabin as well as the galleys and optional forward lavatory. The second duct supplies the aft cabin and aft lavatory. The third duct delivers conditioned air directly from the mixing manifold to the passenger service units (PSU) gaspers.

Question 42

Passenger service units (PSU) gaspers

Answer 42

Most conditioned/re-circulated air enters the passenger cabin at the ceiling. The remainder of the conditioned air is discharged at the cabin sidewalls below the PSU or from the gaspers.
Conditioned air is exhausted from the cabin at floor level. The exhaust air is re-used by the re-circulation system or discharged into the under-floor area.

Question 43

Cargo bay conditioned Air

Answer 43

Both the forward and aft cargo bays are pressurized. Only the aft cargo bay is ventilated by a conditioned air system.
Ventilation and the optional heating of the aft cargo bay are operated from the AIR-CONDITIONING control panel. The system is controlled by the ACSC and continuously monitored. If a fault is detected, the crew is alerted by EICAS.
The forward and aft cargo bays are rated as “Class C” compartments. When smoke is detected in the aft compartment, all ventilating airflow is stopped to create an airtight compartment for containment of the extinguishing agent.

Question 44

Components and operation of cabin Airflow and heating

Answer 44

Ventilating Airflow
Re-circulated cabin air is used to ventilate the aft cargo bay. Air under positive pressure, is taken from the cabin exhaust duct downstream of the left re-circulation fan. An intake shutoff valve on the supply duct controls the flow of air into the aft cargo bay.

When the re-circulation fans are selected off, conditioned air from the mixing manifold becomes the alternate source of ventilating air.
Selecting the CARGO switch to AIR opens the intake and exhaust shutoff valves and allows the aft compartment to be ventilated. When OFF is selected both valves are closed, and airflow through the compartment is stopped.

Optional Heating
Selecting the CARGO switch to COND AIR provides automatic temperature control of the aft compartment.
Controlled by the ACSC, the system maintains the aft cargo bay at a temperature suitable for the transportation of live cargo. When supplementary heating of the compartment becomes necessary, an electric heater is automatically energized. The heater has built-in thermal protection.
When COND AIR is selected and the compartment temperature exceeds the normal range, the heater is de-energized and the CARGO OVHT caution message is displayed. Re-positioning the CARGO switch to AIR removes the caution message from the EICAS primary display.

Question 45

Avionics Equipment Cooling

Answer 45

The flight deck cathode ray tubes (CRT) are cooled and ventilated by airflow to prevent thermal shutdown of the displays. Two fans are utilized; one fan operates on the ground, the other in flight. Either fan can be activated by the pilot to provide backup if the operating fan fail. Should both fans fail, the system is designed to provide a safe amount of air directly from the flight deck air conditioning duct to the CRTs.
Avionics bay equipment uses ambient under-floor air for cooling. An avionics exhaust fan draws airflow through a piccolo tube that is mounted above the equipment to improve air circulation around the equipment

Question 46

Display Cooling

Answer 46

Three separate sources of cooling air guarantee that airflow is provided to the EFIS and EICAS CRT displays to prevent overheating. Only one source is available at any time.
One fan normally operates in flight, the second on the ground. Automatic switching between the two fans occurs at takeoff and landing and is a function of the proximity sensor electronic unit (WOW signal). The fans are controlled by the ACSCs.
The cooling air is exhausted into the free space at the back of the displays. The heated exhaust air is collected by a duct that directs the exhaust air into the aft section of the avionics bay. This exhaust flow is induced by the avionics exhaust fan.
The DISPLAY Fan rotary switch on the center pedestal allows the pilot to select a backup if the operating fan fails. The switch is labeled: GND ALTN, NORM, FLT ALT and STDBY.
A low flow sensor warns of duct blockage or fan failure. The DISPLAY COOL caution message is presented when low airflow is sensed at the CRT displays.

During flight if the fan fails, moving the switch from NORM to FLT ALTN activates the fan normally used on the ground.
On the ground, if the fan fails, moving the switch from NORM to GND ALTN activates the fan normally used in flight.
If both fans fail, selecting STDBY removes power from both of the fans and allows air from the flight deck air conditioning duct to cool the CRTs.

Question 47

Electronic Equipment Cooling

Answer 47

Ambient under-floor air is used for cooling of the electronic equipment in the avionics bay.
The electronic boxes are mounted in racks. Located above each rack a piccolo tube is installed. The avionics exhaust fan creates a suction pressure within the piccolo tube to create air movement around the boxes. From the piccolo tube, the air is discharged by a common exhaust duct into the aft section of the avionics bay.
If the avionics exhaust fan fails, the COOL EXHAUST status message appears.

Question 48

ECS System testing

Answer 48

All components of the pressurization system are continuously tested. When the active controller fails, the standby controller automatically assumes the active role in controlling the pressurization system. A white PRESS CONT 1 (2) FAIL status message is presented.

Question 49

Smoke Detection

Answer 49

Three smoke detector units are provided in the forward cargo bay and two in the aft cargo bay. When smoke is detected, the optional heater is shutdown and the intake and exhaust shutoff valves are closed. Refer to the Fire Protection chapter of this manual for details regarding the Cargo Smoke Detection System.