Atmospheric Pressure

Question 1

What gases and percentages make up the composition of the atmosphere?

Answer 1

Nitrogen: 78%
Oxygen: 21%
Carbon dioxide: 0.04%

Question 2

What are isobars?

Answer 2

Lines on a weather map of places with the same surface pressure

Question 3

What is the pressure in HPA and Hg in ISA?

Answer 3

1013. 25

29. 92

Question 4

What is QNE? What does setting it on an altimeter indicate?

Answer 4

Question Nil Elevation - it is the standard mean sea level pressure in ISA

Setting 1013 will indicate Pressure height or pressure altitude or Flight Level

Question 5

What is the standard pressure lapse rate?

Answer 5

1HPA for every 30FT

Question 6

What is the formula to calculate pressure altitude?

Answer 6

PA = elevation or altitude + (1013 - QNH x 30)

Question 7

What is the definition of air density? What is the ISA density of dry air?

Answer 7

The mass of air occupying a given volume.

1.225KG per cubic metre

Question 8

Decreased pressure = increased or decreased density?

Answer 8

Decreased

Question 9

Decreased temperature = increased or decreased temperature?

Answer 9

Increased

Question 10

Decreased humidity = increased or decreased humidity?

Answer 10

Increased

Question 11

What 3 things effect pressure variation?

Answer 11

1. Movement of pressure systems
2. Changing intensity of pressure systems
3. Semi diurnal pressure variation

Question 12

What is semidiurnal pressure variation? What is it caused by?

Which area of the globe is the effect greatest?

Answer 12

A rhythmic variation in pressure over a 12 hour period caused by the expansion and contraction of the atmosphere as it warms and cools

The tropics (up to 5HPA)

Question 13

What is local QNH?

Answer 13

Actual sea level pressure for a particular location

Question 14

What is validity of area QNH?

Answer 14

3 hours

Question 15

Define a LOW

Answer 15

A centre of low pressure surrounded by higher pressure

Question 16

Define a HIGH

Answer 16

A centre of high pressure by lower pressure

Question 17

Define a COL

Answer 17

A neutral are between 2 highs and 2 lows

Question 18

Define a TROUGH

Answer 18

Any elongated area of low pressure

Question 19

Define a RIDGE

Answer 19

Any elongated area of high pressure

Question 20

What is pressure gradient?

Answer 20

The change in pressure with horizontal distance depicted by isobar spacing

Question 21

Before takeoff on a local flight planned to cruise at FL110 the altimeter subscale should be set to:

a. QFE
b. 1013.2HPA
c. Local QNH if know or aerodrome elevation
d. Area QNH

Answer 21

c. Local QNH if known or aerodrome elevation

Question 22

The QNH setting is the:

a. Height above mean sea level, expressed in hectopascals
b. Atmospheric pressure exerted on a particular area
c. Subscale setting at which altimeter indicates airfield elevation on landing
d. Subscale setting at which altimeter indicates pressure height

Answer 22

c. Subscale setting at which the altimeter indicates airfield elevation on landing

Question 23

The correction applied to station level pressure to obtain QNH assumes:

a. The density of a column of air extending down to mean sea level
b. The density height measured at the station is greater than the pressure heigh
c. The density of a column of air extending down to mean sea level is dependant on the temperature at the station
d. The density height measured at the station is less than the pressure height

Answer 23

a. The density of a column of air extending down to mean sea level is independent of the temperature at station