21 Air Conditioning and Pressurization

Question 1

Where does the pneumatic system draw air from?

Answer 1

From the 8th and 13th stage compressor.

Question 2

When would the pack’s automatically shut-down?

Answer 2

Packs shut-down automatically when an engine fails below 3000’ AGL. If cabin ambient pressure is below 1.3 PSID and engine pneumatic pressure differs more that 70 psi; Packs will shut down. Also, packs shut-down for underpressure and overtemperature conditions.

Question 3

Where is the ram air valve located? @

Answer 3

RT air conditioning system

Question 4

How is the radio rack equipment cooled?

Answer 4

The radio rack equipment is cooled by conditioned air from the flight compartment. When the RADIO RACK Switch is in FAN, the conditioned air from the radio rack is exhausted under the forward cargo compartment floor for heating. When the RADIO RACK Switch is in the VENTURI position, forward cargo compartment heating is not provided, and the air from the radio rack is exhausted overboard through the venturi.
On the ground; both the primary and STBY radio rack fans are on and the venturi valve is closed regardless of the sw. position.

Question 5

How do we know there is active airflow over the instrument panel?

Answer 5

There is an instrument airflow indicator above the gear position indication lights, on the instrument panel. The indications are significant only when on the ground with normal electrical power applied and the air conditioning off.

• ON indicates airflow through the instrument panels.
• OFF indicates failure of instrument cooling fan.

Question 6

If one of the engines fail, AIR COND SHUTOFF in AUTO and the cabin differential pressure is more than 1.3 psi. What happens to the remaining Air Conditioning system?

Answer 6

It continues operation; Below 1.3 psi and engine pneumatic pressures differential by more than 70psi the remaking pack will shutdown. Why do we needed for? What we need is all available power on the remaining engine.

Ref.ASM REV 21 page 14.21.1.11

Question 7

What are some of the usages of the pneumatic system on the MD80?

Answer 7

Pneumatic pressure on the MD80 is used for engine starting, cabin pressurization, air conditioning, ice protection and portable water tank pressurization.

Ref. ASM rev. 21 page 14.21.1.1

Question 8

During pressurized operations; How is the MD80 protected from cabin negative pressure?

Answer 8

Negative pressure is relieved by the inward movement of the galley service, the main passenger entrance door seal and one negative pressure relief valve installed in the aft pressure bulkhead.

Ref. ASM rev.21 page 14.21.1.2

Question 9

What happens when cabin pressure altitudes exceeds 10,000’?

Answer 9

A red CABIN ALT warning light on the EOAP annunciator illuminates, a warning horn would sound for five seconds followed by a voice warning “cabin altitude”. In consequence to the EOAP light illumination, the MASTER WARNING glareshield light also illuminates.

Ref. ASM rev.21 page 14.21.1.3

Question 10

What happens if we inadvertently leave the cabin pressure controller in the MANUAL position during cockpit preflight check, and takeoff in this configuration?

Answer 10

When the CABIN ALT control lever is in the MANUAL position, the control wheel is in the locked position. If we inadvertently depart this way, to control or adjust cabin altitude is by pushing down the control wheel and rotating in the desired direction to be controlled.

Ref. ASM rev.21 page 14.21.1.12

Question 11

How the airplane knows when to depressurize?

Answer 11

When the pressurization system detects a descent (approx. 1,000’ alt. loss) the cabin automatically maintains a cabin differential pressure of 7.77 psi, until the cabin has reached the selected landing altitude.

Ref. ASM rev.21 page 14.21.1.3

Question 12

What is the most significant difference between the two pressurization systems on a Dual automatic pressurization control system?

Answer 12

The two systems are identical but independent. They are powered from different electrical sources, one system has primary control, while the other is on standby.
Ref. ASM rev.21 page 14.21.1.3

Question 13

Why is important to regulate the LT temperature controller before RT Temp controler on the MD80 Air cond system?

Answer 13

Because the RT side is slaved to the LT side via a mix chamber; and the RT system will try to counteract with an opposite reaction to the requested temperature.

Question 14

When would the APU start supplying bleed air after start and in the ground?

Answer 14

After 95% RPM and 60 seconds has passed.

Question 15

With the knob at the index mark; What are the normal cabin climb and descent for the MD80?

Answer 15

700 fpm climb; 300 fpm descent.

Question 16

Normally, where does pressurization receives its electrical power?

Answer 16

Right AC and DC busses; but Left AC and DC busses when pwr is lost to the right busses.

Question 17

Why do we feel a light bump pressure when advancing the throttles on takeoff?

Answer 17

When the throttles are advanced for takeoff, the cabin is pre-pressurized to a slight differential pressure at a slow, comfortable rate. The cabin air outflow valve will open and depressurize the cabin if either throttle is retarded or ground shift does not occur within 60 seconds of initial power application.

Question 18

During anti-ice operations; pneumatic pressure must be at a minimum Off?

Answer 18

20 psig.

Question 19

What does placing the pneumatic X-feed valve to CLOSE; accomplishes?

Answer 19

It shuts off engine bleed air for airfoil ice protection and pneumatic crossfeed starts. Each air cond. pack is supplied bleed air from its respective engine.

Question 20

What is the function of the recirculating fan?

Answer 20

It returns the cabin air to the overhead ducts for PAX cabin air recirculation. The fan has no cockpit control or indication and will operate in flight only. Located fwd of the rear pressure bulkhead.

Question 21

Where does the PNEU PRESS indicator taps its pressure information?

Answer 21

X-feed manifold.

Question 22

What does a (L/R) AIR COND TEMP HIGH may indicate?

Answer 22

Air conditioned pneumatic supply exceed normal operating temperature. May indicate a malfunction of augmentation valve.

Question 23

With RADIO FAN sw in FAN; When does the RADIO FAN OFF annunciator comes on?

Answer 23

In flight, when the primary and stby fans are inop.

On ground, if primary fan is inop.

Question 24

Why is the Air conditioning AUTO mode normally used for takeoff on the MD80?

Answer 24

Because pack shutdown protection is inhibited in any other mode.

Question 25

When is the augmentation valve open?

Answer 25

When the AIR COND SUPPLY sw is in the AUTO position and the 8th stage bleed air pressure no longer meets system demand on the appropriate side.

Question 26

When selecting a new air cond temperature; where would first be reflected that the temp control valve has moved?

Answer 26

Valve position indicator.

Question 27

What happens with the cabin pressurization system when the throttles are advanced for takeoff?

Answer 27

The cabin is pressurized for 60 seconds unless a rejected takeoff occur or the aircraft is detected airborne.