GLOSSARY

Air pressure


Air pressure (P)

The air pressure of any place in the earth’s atmosphere is the pressure of the air, existing at this place. It indicates the weight power of the air column standing above a surface or body.

Barograph

Is a measuring instrument which records the time course of the air pressure on a chart-stringed drum.

Barometer

Is a measuring instrument for determination (display) of air ­pressure, and is used in a variety of different forms and types mostly in the field of meteorology.

Barometric Altitude Formula

Indicates the vertical change of the air pressure with the altitude.
Simplify you may assume that close to the sea level the air pressure declines by one hPa per 8 m altitude.

Baro transmitter

Is a measuring instrument with electrical measuring value Output.

Barometric Unit

Unit of the air pressure is the Pascal.
As the air pressure on sea level is, on average, 101325 Pa, thus approx. 100000 Pa, it is given mostly by the number about 1000 in hectopascal (1013.25 hPa) or by the same numerical value millibar (mbar). The air pressure is mostly measured through a barometer, where often obsolete units are used. Here is: 1 hPa = 1 mar = 0.75 Torr (= mm Hg or millimeter mercury column).

QFE

QFE means the air pressure of aerodrome/airport on the runway. If QFE is set at the altimeter (for ex. before start or landing) you achieve the barometric air pressure or height related to the airport height. On the airport the altimeter ­indicates then a height of 0 m or 0 ft.

QFF

QFF is the current air pressure at the measuring site (for ex. aerodrome/­airport), reduced to the sea level. It is used in the field of meteorology in order to ­compare the air pressures of different places at different heights.
The ­calculation is carried out with ASL (altitude above sea level) and data of the “current atmosphere” (pressure, temperature, and humidity).

QNH

The abbreviation QNH means the air pressure at the measuring station, reduced to sea level acc. to “standard atmosphere”.
It serves for setting an altimeter which displays the flight altitude above sea level. After landing of the aircraft, the altimeter displays the altitude of site above sea level.

Standard atmosphere

Is a term used in aviation. Characteristics like pressure, temperature, or temperature course with the altitude are subject to special and time changes in the atmosphere. The standard atmosphere indicates an average state of the atmosphere.

TA

Transition Altitude (TA) is a term used in aviation. It indicates the altitude where the transition of the altimeter setting from standard air pressure to the currently existing air pressure QNH is carried out or vice versa.

TL

Transition Level (TL) is the lowest flight level available for use which has a ­minimum distance of 1000 ft above the transition altitude. Therefore the ­Transition Level is depending on the air pressure. In some regions of Germany the Transition Altitude is, generally, 5000 ft.
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