Transition height
The transition altitude and the associated transition area describe certain flight altitudes in aviation , at which the reference value for the barometric measurement of the flight altitude changes.
- With Transition Altitude (TA) (German: transition altitude) refers to the height at which the climb , the altimeter of the current meteorological reference pressure ( QNH ) to the standard air pressure is changed (1013 hPa). This means that the flight altitude is no longer measured as altitude above sea level, but as altitude above the theoretical normal pressure surface.
- With Transition Level (TRL) (German: transfer surface) the flight level referred to in the descent of the altimeter from standard air pressure on QNH is changed - that is reverse to the transition altitude. The transition level is set according to the current air pressure so that it is above the transition altitude.
- The transition layer is the area between transition altitude and transition level.
The abbreviations TA and TRL are always pronounced in English in full. There is no shortcut for the transition layer.
Memory aid
In TA, the A symbolizes the up arrow - for climbing. In TRL, the L symbolizes the down arrow (with a little imagination) - for the descent. Or: The altitude according to QNH is always referred to as altitude and that according to standard air pressure is divided into flight level (FL). If we now increase from below with a Altitude , one uses the T A , one drop from a flight level down, it is analogous to the TR L .
Explanation
The transition area is the lowest usable flight area , which has a minimum distance of 1000 ft to the transition height. This minimum distance is known as the transition layer.
Therefore the transition area depends on the air pressure ( transition areas in Germany ). The transition height is usually only changed for organizational reasons and is 5,000 ft in Germany and 10,000 ft in Austria.
In order to set the barometric altimeter in an aircraft, which determines the flight altitude based on the air pressure, an aircraft pilot receives the so-called QNH from a ground location , which is specified in hPa . If this value is set on the ground in the altimeter, it indicates the height of the ground location above sea level (MSL from mean sea level ), while in the air the altimeter shows the aircraft's altitude above MSL.
Since the prevailing air pressure can constantly change (which is still supported by moving to another place), the QNH only ever applies to the place and time at which it was transmitted.
In order to ensure the altitude coordination of aircraft on cross-country flights, the QNH is no longer set in the altimeter (in Germany) from an altitude of 5000 ft above MSL, but the standard value 1013 hPa. With this procedure, the altimeters of different aircraft always show a comparable value for cross-country flights (which does not necessarily indicate the real altitude above MSL). This saves aircraft in cross-country flights having to permanently adjust their altimeter to local QNH. Since with standard air pressure all aircraft have "equally wrong" altitude settings, the minimum distance is ensured.
As soon as the altimeter is changed by the QNH to the standard value 1013 hPa, the flight altitude is no longer referred to as altitude, but as flight level / flight level, which is given in full hundreds. Flight level 75 (Flight Level 75) means z. B. 7,500 ft at 1013 hPa.
In order to obtain a reliable altitude value for the selected landing site when landing (or later take-off), the default value is set back to the current QNH when approaching the landing area (a pressure-dependent flight area defined for the landing site).
This results in two standard procedures:
- Start with QNH / change to 1013 hPa when the transition altitude is reached (in Germany 5,000 ft)
- Landing approach with 1013 hPa / change to QNH when reaching the transition area
Necessity of two transition heights
Two different transition heights are necessary so that the minimum distance between the "upper system" (flying according to the standard pressure) and the "lower system" (flying according to the current pressure - QNH) is never fallen below.
The upper limit of the "lower system" is the transition height (TA).
The lower bound of the "upper system" is the transition area (TRL). This should have a safety distance of min. Ensure 1000ft to the "lower system" to prevent dangerous overlap. However, this would be the case at low air pressure values (low pressure area ). Thus, the TRL is moved further upwards for safety during a low pressure phase.
If the surrounding air pressure is lower than the air pressure set on the altimeter, the displayed altitude is greater than the altitude flown (approx. 27 ft per hPa).
During a descent, the pilot needs information about the altitude at which the transition area is currently and how high the current, local air pressure ( QNH, specified in inHg or hPa ) is near the space. He gets this information with the other landing information via the ATIS .
Safety distance (transition layer)
In aviation, minimum distances must be observed between the flight areas. Differences in air pressure between standard and local air pressure could lead to the distance between the "upper" system and the "lower" system falling below this safety distance. B. Less than 1,000 feet between flight level 060 (at standard pressure) and 5,000 feet (at local atmospheric pressure).
Therefore, depending on the local air pressure, the distance between "upper" and "lower" (the transition layer) is different "thick". The surcharge is determined according to the following table:
QNH -977: +3000ft QNH 978-1013: +2000ft QNH 1014-1050: +1000ft QNH 1051+: + 0ft
(Read: At QNH below 977 hPa, 3000 feet is added between the altitude in local air pressure and the next flight level in standard air pressure: 5000ft -> FL 050 + 30 = FL 080. Or: With TA 5000ft and QNH below 977 the TRL 080.)
The transition layer is never subtracted from the transition level, but always added to the transition altitude (TA).
These regulations result in the following stratifications:
Reiseflughöhen: in FL (100ft) mit Standard-Luftdruck QNH 1013 -- Transition Level (TRL) : Untergrenze der Zone mit Standard-Luftdruck = TA + Transition Layer Transition Layer: variiert je nach lokalem Luftdruck -- Transition Altitude (TA): Obergrenze der Zone mit lokalem Luftdruck Lokaler Luftdruck (bis zum Boden)
Transitional areas in Germany
| QNH off | QNH to | TRL |
|---|---|---|
| 943 | 977 | 80 |
| 978 | 1013 | 70 |
| 1014 | 1050 | 60 |
| 1051 | 50 |
Transitional areas in Austria
Since spring 2016, all transition heights in Austria have been increased to 10,000 feet. The transition areas in Austria are therefore, depending on the QNH:
| QNH off | QNH to | TRL |
|---|---|---|
| 943 | 977 | 130 |
| 978 | 1013 | 120 |
| 1014 | 1050 | 110 |
| 1051 | 1088 | 100 |