Flight level#Transition altitude

The transition altitude (or transition surface ) describes a flight height in the aviation industry, in which a change in the calibration of the altimeter occurs.

  • With transition altitude (TA ) ( German: transition altitude ) is the amount designated, which when in the ascent of the transition of the altimeter setting from ( QNH) to the standard atmospheric pressure (1013 hPa).
  • With Transition Level (TRL ) ( German: transition area) at flight level is referred to, in which the descent of the transition of the altimeter setting from the standard air pressure on the QNH is carried out - ie reverse to the transition altitude.
  • The Transition Layer ( German: transition layer ) is the area between the transition altitude and transition level.

The abbreviations TA and TRL are always pronounced in English in full length. For the transition layer there is no shortcut.

Memory aid

In the TA, the A symbolizes the up arrow - for the climb. In the TRL L symbolizes the down arrow ( with some imagination ) - for the descent. Or: It is the height after QNH altitude than ever and that is by standard air pressure at Flight Level (FL ) divided. Climbing up now from the bottom with an altitude, one uses the TA, you sink down from a flight level is analogous to the TRL.

Explanation

The transition area is the lowest usable flight level, which has a minimum distance of 1000 ft to the transition altitude. This minimum distance is called the transition layer.

Therefore, the transition area affected by atmospheric pressure ( transition areas in Germany ). The transition altitude is generally altered for organizational purposes only and in Germany is 5,000 ft.

To an aircraft which determines the altitude based on barometric pressure, adjust the analog altimeter, aircraft commander receives from a ground point, the so-called QNH, which is given in hPa. If this value is set on the ground in the altimeter, this is the amount over the ground point above sea level ( MSL of Engl. Mean sea level ), in the air, the altimeter will analogously, the altitude of the aircraft above MSL at.

Since the prevailing air pressure can change constantly (which is still supported by the movement to another location ), the QNH is only valid for the place and the time at which it was transmitted.

To ensure the level coordination of aircraft -haul flights, ft ( in Germany ) from an altitude of 5000 is no longer the QNH but the default value set 1013 hPa above MSL in the altimeter. By this method always show the altimeter of different aircraft at haul flights a comparable value ( the case but not necessarily indicative of the true height above MSL).

Once the altimeter to the default value is 1013 hPa changed from QNH, it is called at the altitude not more of Height / Altitude but from flight level / flight level, which is rounded to full hundreds. Flight level 75 ( Flight Level 75) means, for example, 7,500 ft at 1013 hPa

To regain during a landing (or the later start ) a reliable height value for the selected landing site, is provided on the landing approach in reaching the transition area (one set for the landing site luftdruckabhängingen flight level ) from the default value to the current QNH.

This leads to two standard procedures:

  • Start with QNH / change to 1013 hPa at reaching the transition altitude ( in Germany 5,000 ft)
  • Landing with 1013 hPa / change to QNH when reaching the transition area

Need for two transition heights

There are two different transition altitudes necessary so that the " top System" ( fly to standard pressure) and the "lower system " ( fly to current pressure - QNH) never overlap. The upper limit of the " lower system " is the transition altitude (TA).

The lower limit of the " upper system " is the transition area (TRL). This is a safety distance of min. 1000ft to ensure " lower system " in order to prevent dangerous intersections. This would be niederigen air pressure values ​​( low pressure area ) but the case. Thus, the TRL will be further postponed during a low pressure phase to the safety upwards.

If the surrounding air pressure lower than the set on the altimeter barometric pressure, the indicated altitude is greater than the height flown (about 27 ft per hPa).

When descending, the pilot therefore needs to know at what height the transition area is currently located and how high the current local barometric pressure ( QNH, given in inHg or hPa) near the camp is. This information it obtains with the other country information on the ATIS.

Transition areas in Germany

  • Air traffic control
Descent (aeronautics)
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