B737NG Air Systems

Question 1

What will cause a BLEED TRIP OFF Light?

Answer 1

Exceeded engine bleed air temperature or pressure

Question 2

What will cause a ‘PACK TRIP OFF’ light to illuminate?

Answer 2

Respective pack has exceeded temperature limits and has tripped off

Question 3

What does amber Equipment Cooling, Supply or Exhaust ‘OFF’ Light indicate?

Answer 3

There is no airflow detected coming from the respective cooling exhaust or supply fan.

Question 4

Where does the flight deck receive its conditioned air from?

Answer 4

LEFT pack, upstream of the mix manifold, flows directly to the flight deck.

Question 5

How many packs are required to maintain pressurisation up to FL410 ?

Answer 5

A single pack IN HIGH flow is capable of maintaining pressurization up to the maximum certified ceiling.

Question 6

When the aircraft is on the ground or the flaps are down with the packs in AUTO, will the packs still automatically change to high flow, if operating on one pack only?

Answer 6

No, automatic switching to high air flow is inhibited in this situation to ensure adequate engine power is available for single engine operations.

Question 7

What is the purpose of operating the packs in AUTO during normal operations in flight?

Answer 7

Incase one pack stops supplying air, the remaining pack automatically switches to high air flow to increase ventilation.

Question 8

What is is the purpose of the Ram Air System?

Answer 8

Provides cooling air for the heat exchangers.

Question 9

How is the Ram Air System controlled and operated?

Answer 9

The system is automatically controlled by the packs through the operation of the ram inlet doors.

Question 10

What are the four steps of the cooling cycle?

Answer 10

1. Bleed air passes through heat exchanger for cooling.
2. Air then flows to Air Cycle Machine for refrigeration and water separation.
3. The cold air is then ‘conditioned’ and combined with hot air.
4. The conditioned air is then distributed by the mix manifold.

Question 11

What happens to the Air Mix valves if the pack valves close and why?

Answer 11

The air mix valves drive to full cold position in order to aid startup of the cooling cycle and prevent hot air trips when the packs are turned back on.

Question 12

What is the purpose of the Recirculation fans?

Answer 12

To reduce engine bleed air demand and air conditioning system pack load.

Question 13

What happens to the Equipment cooling exhaust fan if there is a Forward Cargo Fire warning?

Answer 13

The equipment cooling exhaust fan SHUTS OFF, and the ‘OFF’ light is inhibited.

Question 14

How many automatic cabin pressure controllers are fitted to INU?

Answer 14

Two

Question 15

How is the pressurisation controlled?

Answer 15

By modulating the outflow and overboard exhaust valve.

Question 16

What is the purpose of the PRESSURE RELIEF VALVES?

Answer 16

To provide safety pressure relief incase the cabin differential pressure EXCEEDS 9.0 PSI.

Question 17

What is the maximum cabin differential pressure?

Answer 17

9.1PSI

Question 18

How many pressure relief valves are there and what are they called?

Answer 18

Two, a pressure relief and one negative relief valve.

Question 19

Where do BOTH the Cabin Pressure controllers receive their altitude and pressure data from?

Answer 19

ADIRU’s, which receives barometric corrections from the BARO reference selectors (QNH)

Question 20

Why does the outflow valve modulate towards ‘closed’ position when thrust is increased during the take off roll?

Answer 20

Ground pressurization of the cabin makes the transition to pressurized flight more gradual for the passengers, and also gives the system better response to ground effect pressure changes during takeoff.

Question 21

What are the pressurisation controllers programmed to do if the amber ‘OFF SCHED DESCENT’ light illuminates?

Answer 21

The controller programs the cabin to land at the takeoff field elevation without further pilot inputs. (Assumes return 4 landing)

Question 22

What happens if the FLT ALT indicator is changed, after an amber ‘OFF SCHED DESCENT! light illuminates?

Answer 22

The automatic abort capability to the original takeoff field elevation is lost.

Question 23

What happens if the FLT ALT indicator is changed, after an amber ‘OFF SCHED DESCENT! light illuminates?

Answer 23

The automatic abort capability to the original takeoff field elevation is lost.

Question 24

What triggers pressurisation to change from climb, cruise or descend mode?

Answer 24

When the airplane climbs or descends to within/outside of 0.25 psi of the selected FLT ALT.

Question 25

When is manual control of the cabin altitude required?

Answer 25

If both the AUTO and ALTN modes are inoperative or during a non-normal situation.

Question 26

How is the pressurisation controlled when in Manual mode?

Answer 26

By manually positioning the outflow valve using the Outflow Valve switch.

Question 27

What system of pressurisation will operate the outflow valve fastest?

Answer 27

In MAN mode, a separate DC motor, powered by the DC standby system, drives the outflow valve at a faster rate than during AUTO or ALTN modes. (Approximately 20 seconds for a full valve movement)

Question 28

How should the outflow valves be treated when manually opening or closing the valve?

Answer 28

A very small movement of the outflow valve is recommended at one time.

A small movement of the outflow valve can cause a large change in cabin rate of climb or descent. Manual actuation of the outflow valve can produce large, rapid changes in cabin pressure which could result in passenger and crew discomfort and/or injury.