Pressure Flashcards Preview

ATPL Meteorology > Pressure > Flashcards

Flashcards in Pressure Deck (47)
Loading flashcards...
1

The atmosphere is composed of a variety of gases these are....

Nitrogen (78%)
Oxygen (21%)
Carbon Dioxide (0.04%)
Other

2

What is atmospheric pressure defined as?

Combined weight of gases exerting force in all directions

3

What is used to measure atmospheric pressure?

A Barometer

4

What is pressure expressed as?

Inches or Millibars of Mercury
Millibar
Hectopascal

5

A hectopascal is equal to...

100 newtons per square metre

6

What is an isobar?

The line on the map to indicate locations of the same pressure

7

What happens to pressure as you increase altitude?

Reduces

8

What is the ISA pressure at sea level?
In HPA, Hg and lb/sq.in

1013.25 HPA
29.92Hg
14.7lb/sq.in

9

What is QNE (Question Nil Elevation)?

Setting 1013 on aircraft subscale

QNE is a pressure setting of 29.92 inches or 1013 hPa that will produce a standard atmosphere altitude and provides the basis for flight levels.

10

With QNE set on the altimeter, the main scale will indicate?

Height above or below 1013 HPA Pressure level
(Pressure height or Pressure Altitude)

11

At low level, the pressure reduces at a rate of...

1 HPA / 30ft of altitude increase in the troposphere

=1 Hg / 1000ft

12

Air density refers to....

Mass of air occupying a given volume

13

What 3 factors does air density depend on?

- Temperature
- Humidity
- Pressure

14

Decreased Pressure= .... Density

Decreased Density

15

Increased Temperature=

Decreased Density

16

Increased Humidity=

Decreased Density

17

Does high density give better or worse aircraft performance?

Better

18

Why do variations in pressure occur?

- The movement of pressure systems
- Changing the intensity of pressure systems
- Semi diurnal Pressure variation

19

What is semi-diurnal variation?

Rhythmic variation in pressure over 12 hour period

20

Where is semi-diurnal variation the greatest?

Tropics
Can change up to 5 HPA

21

What is standard pressure?

1013.25 HPA

22

What is the actual mean sea level pressure referred to as?

QNH

23

When QNH is set on altimeter it will read...

Altitude (Height above mean sea level)

24

What is local QNH?

Actual sea level pressure for a particular location

25

Where is Local QNH available?

Control tower or ATIS

26

If you set the airfield elevation on your altimeter what will it read?

Approx. Local QNH

27

What is area QNH?

Predicted average sea level pressure

28

Who forecasts area QNH?

Bureau of Meteorology

29

How often is area QNH updated?

Every 3 hours

30

Area and Local QNH can differ, but by how much?

5 HPA