8.10 Atmospheric Pressure and Density

8.10.2 Define ‘atmospheric pressure’.

Atmospheric pressure is the force exerted by the weight of the air above a given area.

Air has mass, and therefore weight. The more air there is above a point, the greater the pressure at that point.

At mean sea level, the standard atmospheric pressure is:

1013.25 hPa

This is approximately equal to:

14.7 psi

Atmospheric pressure decreases with height because there is less air above the aircraft as altitude increases.

8.10.4 State the pressure units used in New Zealand aviation.

The basic SI unit of pressure is the pascal (Pa).

In New Zealand aviation, atmospheric pressure is normally expressed in:

hectopascals (hPa)

One hectopascal equals 100 pascals:

1 hPa = 100 Pa

Therefore:

101,300 Pa = 1013 hPa

The standard mean sea level pressure used in aviation is:

1013.25 hPa

This is often rounded to:

1013 hPa

8.10.6 State the significance of air pressure to aviation.

Air pressure is significant to aviation because it affects:

• aircraft performance
• engine performance
• weather
• altimeter readings