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737 Systems > Pressurization & Air Systems > Flashcards

Pressurization & Air Systems Flashcards

1
Q

Describe the valves used in the bleed air system.

A

Butterfly type. Their main advantage is that they can open and close very quickly, they are reliable and precise.

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2
Q

How many packs should one engine operate?

A

One engine should only operate one pack at a time.

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3
Q

When using an external pneumatic source what is the pressure and temperature limitation?

A

60 PSI and 232°C (450°F)

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4
Q

What PSI is considered high when the engine is the bleed air source?

A

Above 50 PSI is considered high and requires maintenance action

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5
Q

Which engines stages are used for the bleed air source?

A

The 5th and 9th stage.

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6
Q

What triggers the DUAL BLEED light?

A

Illuminates when the Apu bleed air valve is open and:
-engine one bleed air switch on OR
-engine two bleed air switch on with isolation valve open

Operate the engines at idle thrust only (engine bleed could otherwise back pressure the Apu and cause damage)

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7
Q

What triggers the BLEED TRIP-OFF light?

A

Over temperature (254° c / 490° f) or overpressure (220 PSI) is sensed

PRSOV automatically closes to prevent damage to the duct

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8
Q

What is a likely cause of the BLEED TRIP-OFF light and how is it reset?

A

Can happen especially after no engine bleed take-off with high engine thrust.

To reset the bleed trip off the conditions have to return a load limit and trip reset switch has to be pressed

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9
Q

What triggers the WING-BODY OVERHEAT light?

A

A leak in the bleed air duct
An overheat condition is sensed

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10
Q

If a WING BODY OVER HEAT light illuminates what should you watch out for and what can you not use?

A

Watch out for subsequent A/C or pressure failures on the opposite side

Do not use wing anti-ice

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11
Q

What messages can be reset by the TRIP RESET switch?

A

BLEED TRIP-OFF
PACK
ZONE TEMP

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12
Q

What does the FCSV do?

A

Flow Control Shutoff Valve

Controls the amount of air the packs get for cooling depending on the pack switch position.

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13
Q

What two valves does the trim air pass though?

A

PRSOV & FCSV

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14
Q

Describe the FCSV.
Fails open or closed, controlled, actuated

A

Spring loaded closed
Electrically controlled (BAT BUS)
Pressure activated

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15
Q

Pack Switch to OFF, what happens?

A

-FCSV receives electric signal to close (BAT BUS)
-No bleed air to packs it trim air system
-If both pack switch OFF, no fresh air into cabin and cabin will gradually depressurize

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16
Q

Pack switch AUTO, normal vs HIGH flow

A

Normal flow when 2 packs are operating (55 pounds/minute)

HIGH flow provided when:
-Single PACK operation with flaps up in-flight (80 pounds/min)
-Single PACK operation with APU bleed ON, and both engin bleed air switches OFF (regardless of flap or air/ground status)

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17
Q

Pack switch HIGH

A

PACK will provide high flow (100 pounds/min)

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18
Q

Where do the PACKS supply air?

A

Left pack supplies the flight deck and excess goes into mix manifold.

Right pack normally supplies only mix manifold.

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19
Q

Recirculating Fans, how many, purpose, powered by?

A

Two fans draw air from the passenger cabin though HEPA filters then return to the mixing manifold. When both are on 50% of the air is recycled reducing the load on the PACKS thus increasing fuel economy. Fans are driven by AC motors.

20
Q

How many temperature control zones and what range of temperature can be set

A

3 zones (Flight Deck, Forward and Aft)
65°F to 85°F

21
Q

With the temperature control zones set to different values, what temperature will the PACKS output be? How will the other temperatures be created?

A

Normally packs will output the coldest temperature setting. The remaining zones are heated up by trim air.

22
Q

What does selecting TRIM AIR off do?

What if both TRIM AIR are switched off?

A

TRIM AIR off closes the Trim Air Modulating and Shutoff Valve.

When all selectors OFF:
L PACK 75°F,
R PACK 65°F
(measured at pack sensor)

23
Q

Describe how the PACKS operate in Balanced Mode (normal)

A

Both PACKS produce the same temperature equal to the zone which requires the most cooling. TRIM air heats the remaining two zones.

24
Q

Describe both why and how the PACKS operate in Unbalanced Mode

A

Flight Deck trim air fails (CONT CAB)

L PACK = controlled for requirements of the flight deck

R PACK = cabin zone which requires most cooling

25
Q

Describe both why and how the PACKS operate in Unbalanced Average Mode

A

TRIM AIR switch is OFF or either passenger temperature zone fails

L PACK = controlled for requirements of the flight deck

R PACK = average temperature requirements of the two cabin temperature zone

26
Q

What causes a CONT CAB light?

A

With MASTER CAUTION:
Duct Temperature Overheat (88°C)
-OR-
Failure of both Primary and Standby Temperature Control

ON RECALL:
Failure of Primary or Standby Temperature Control

27
Q

Describe the fans used in the equipment cooling

A

Supply and Exhaust ducts have two fans (NORM and ALTN)

One fan operates per duct at a time.

Fans have an overheat sensor which will turn them off

Powered by 115V AC

28
Q

For the equipment cooling fans, depending on the position of the EXHAUST VALVE, where does the Exhaust go?

A

Exhaust is either vented overboard though the overboard exhaust valve OR around the forward cargo compartment.

29
Q

In the event of a forward cargo fire what two things happen in regard to the equipment cooling fans?

A

The equipment cooling exhaust fan is Shutoff

The equipment cooling exhaust fan OFF light is inhibited.

30
Q

If the crew call horn located in the nose wheel is sounding, what is the cause?

A

Insufficient flow in the equipment cooling supply.

31
Q

If the equipment cooling OFF Light is illuminated what should you do, what could this signal?

A

Indicates insufficient airflow

Selecting the alternate fan should restore airflow and extinguish the OFF light within approx 5 second

Distribution of airflow can signal impending pressurization problems

32
Q

Outflow Valve:
Location, controlled, number and type of motors

A

Located below the right horizontal stabilizer

Two CPCs but can also be operated manually

Three DC motors, two controlled by their own CPC (DC BUS #1 and DC BUS #2). One manually (BAT BUS)

33
Q

Is there a safety mechanism in the Outflow Valve?

A

Yes, as long as one CPC controls the valve it will automatically force the valve closed when the cabin altitude is above 14,500 ft.

34
Q

Describe the CPCs

A

Two identical CPCs operate in AUTO or ALTN mode. One active at a time and switch each flight. Powered by DC BUS #1 and DC BUS #2.

35
Q

With a loss of all sources of AC power, how is pressurization controlled, why?

A

Manually because DC BUS #1 and DC BUS #2, the electrical sources of the CPCs and related motors are not powered.

36
Q

What is the different pressure limit…
At and below FL280
FL280 - FL370
Above FL370

A

7.45 = At and below FL280
7.80 = FL280 - FL370
8.35 = Above FL370

37
Q

Pressurization AUTO FAIL Will illuminate when:

A

DC power is lost

Controller fault

Outflow valve control fault

Excessive differential pressure (over 8.75 psí with no correction)

Excessive rate of cabin pressure change (over 2000 ft/min with no correction)

High cabin altitude (above 15,800ft with no correction)

38
Q

After an AUTO FAIL light Illuminates, what should happen? What if it does not happen?

A

The ALTN light should come on automatically to signal backup CPC coming online

If the ALTN light does not illuminate, both CPCs were lost, pressurisation has to be controlled manually.

39
Q

When will the OFF SCHED DESCENT Light illuminate?

A

The light will illuminate when a descent starts before reaching the altitude selected in the FLT ALT pressurisation window, indicating that off-scheduled Descent Mode is active

This means that LAND ALT is discretely set to the departure airport (for possible air turn back)

40
Q

The OFF SCHED DESCENT will extinguish and logic resets when:

A

FLT ALT is reset to current altitude

Airplane starts to climb again

Pressurization Mode Selector is in MAN

Airplane lands

41
Q

Prediction MANUAL Light indicates.

A

Pressurisation Mode Selector is in MANUAL mode and the flight crew has direct control over the outflow valve.

42
Q

What has failed if both AUTO FAIL and ALTN lights illuminate?

A

A single CPC failure has occurred

43
Q

Describe the Cabin Pressure Relief System

A

Two positive pressure relief valves set to open at 9.1 psi

One negative relief valve set to open at -1.0 psi

44
Q

What is set before take-off for pressurisation? When is a supplementary procedure used?

A

Both FLT and LAND ALT are set before take-off

Highest expected cruising altitude shall be selected in FLT ALT

FLT ALT Range -1,000ft to 42,000ft (500ft increments)

LAND ALT Range -1,000ft to 14,000ft (50ftincrements)

When landing at an airfield above 6,000 ft, there is a supplementary procedure for setting landing altitude

45
Q

Following non-normal conditions may lead you to control the cabin pressurisation manually:

A

Cabin Altitude Warning or Rapid Depressurisation

Tail Strike

PACK, BLEED TRIP-OFF, WING-BODY OVERHEAT

AUTO FAIL or Unscheduled Pressurisation Change (750FPM)

Loss of AC Power Sources (DC BUS 1 and 2 unpowered)

Landing Gear Will Not Move Up After Take-off (air-ground sensor stuck in ground, CPCs will open the OFV when thrust is reduced)

Cabin Temperature Hot

46
Q

According to the Boeing FOTB, the cabin altitude is considered uncontrollable when one of the following is true:

A

Cabin altitude rate exceeds 750 FPM in AUTO or ALTN mode

Cabin altitude rate cannot be controlled manually

Cabin altitude exceeds 15,000 ft regardless of whether the cabin rate can be controlled or not (it would take excessively long to decrease the altitude below 10,000 ft)

737 Systems (8 decks)

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