14.36 Pressure Instruments

14.36.2 Identify the three basic instruments which rely on air pressure for their operation.

The three basic instruments that rely on air pressure are:

• Airspeed Indicator (ASI)
• Altimeter
• Vertical Speed Indicator (VSI)

These are collectively known as the pitot-static instruments, as they operate using pitot and/or static air pressure.

14.36.4 Describe static pressure and dynamic pressure, and the main factors which affect them.

Static Pressure:

• The ambient air pressure exerted by the atmosphere at a given point
• Acts equally in all directions
• Independent of aircraft movement

Factors affecting static pressure:

• Altitude: increases → pressure decreases
• Temperature: warmer air tends to reduce pressure (less dense air)
• Atmospheric conditions (pressure systems/weather)

Dynamic Pressure:

• The pressure due to the motion of air (kinetic energy)
• Depends on the aircraft’s airspeed through the air
• Acts in the direction of airflow