International Standard Atmosphere

Question 1

What is the ISA?

Answer 1

International Standard Atmosphere is a model of average atmospheric conditions around the globe and is used as an international standard.

Question 2

How is the ISA applied?

Answer 2

Aircraft instruments calibrated to react correctly based on ISA. Any deviation requires compensation.

Question 3

What are the various “spheres” of the atmosphere?

Answer 3

Troposphere
Stratosphere
Mesophere
Thermosphere

Question 4

What altitude does the tropopause start? What noticeable effect is there?

Answer 4

36,089ft / 11km.

Temperature remains constant until 65,600ft /until 20km

Question 5

What is the distribution of air mass through the standard atmosphere?

Answer 5

75% air mass below tropopause
50% in first 5.5km
remaining 25% above tropopause

Question 6

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

Answer 6

78% Nitrogen
21% Oxygen
1% trace gases