Key Atmospheric Terms- Elevation, QNH, Altitude, and Height
Aspiring pilots must comprehend various meteorological terms to ensure safe and precise flying. This section covers essential terminology related to atmospheric pressure and altitude, crucial for the CASA PPL (Private Pilot License) theory exam under the topic of Meteorology > Heat, temperature pressure and humidity.
Elevation
Definition
Elevation refers to the height of a specific location above a predefined reference surface, commonly sea level or the ground at an airport. It serves as a static, physical measurement distinguishing it from flight-based vertical references like ‘altitude’ or ‘height’.
Source
QNH (Altimeter Pressure Setting)
Definition
QNH is the atmospheric pressure adjusted to sea level pressure, used as a setting on an aircraft’s altimeter. When the altimeter is set to the current QNH value, it displays the altitude above mean sea level. This setting is crucial for maintaining safe separation between aircraft in flight and is typically reset when entering different pressure regions.
Standard QNH
A standard value of 1013.25 hPa is frequently used above the transition altitude.
Mnemonic
“Nautical height” can help remember its association with sea level.
Sources
- Altimeter Pressure Settings - SKYbrary
- QNH, QNE, and QFE: Altimeter Settings - aviationfile.com
- Altimeter setting - Wikipedia
Altitude
Definition
Altitude is the vertical distance of an aircraft above mean sea level. It is a dynamic value dependent on the current atmospheric pressure readings and is essential for navigation and safety.
Sources
Height
Definition
Height refers to the vertical distance from an aircraft to a specific reference point on the ground, such as the elevation of an airfield. When using QFE settings on an altimeter, the height is indicated above the reference datum of that airfield.
Sources
QFE (Field Elevation Pressure Setting)
Definition
QFE is the atmospheric pressure at a specific location, like an airfield. Setting the altimeter to QFE will read zero when the aircraft is on the runway. It is used to measure the height above a particular airfield.
Mnemonic
“Field elevation” helps recall its relationship to specific geographic locations.
Sources
- Altimeter Pressure Settings - SKYbrary
- QNH, QNE, and QFE: Altimeter Settings - aviationfile.com
- Altimeter setting - Wikipedia
By understanding these terms, pilots can accurately interpret altimeter readings and ensure safe aircraft operation concerning the Earth’s surface.