Flight level
A Flight Level ( english flight level, FL) called in aviation a surface of equal air pressure in the atmosphere. An airplane following a flight level, shows a constant altimeter indication. By assigning flight levels of air traffic control aircraft are staggered vertically, that is, to ensure safety distances.
- 2.1 climb
- 2.2 descent
Definition
The flight level is the level at 100 feet ( ft) above that height, in theory, standard pressure ( 1013.25 hPa) exists. All aircraft flying in the flight surfaces, therefore their altimeter set to a reference air pressure of 1013.25 hPa; the display in feet divided by 100 gives the flight level.
Deviations of the idealized ICAO standard atmosphere of the real atmosphere does not fall into this weight because the measurement error for all involved planes is the same, so that the proper vertical separation is maintained.
The actual height of a flight surface is dependent on atmospheric conditions, especially by the current pressure: so is a, for example, and the same flight level in a high pressure area higher above the ground than in a low-pressure area. That does not bother in the airspace, however. It comes in cruise not the actual height, but only to the vertical separation of aircraft among themselves.
Examples
- If on the ground, an air pressure of 1013.25 hPa, so there is flight level 100 at 10,000 feet (3,048 m) above ground level ( assuming standard conditions ).
- If on the ground, an air pressure of only 995 hPa ( approximately in a low pressure area ), so there is the (imaginary ) Normal pressure surface 500 feet below ground. Flight level 100 is below standard conditions 10,000 feet about it, so in this case 9500 feet ( ~ 2900 m) above the ground.
Since the extent of altitude-related decrease in air pressure also still slightly dependent on the air temperature, the actual distance of the flight level can vary 100 ft to the normal printing area by a few percent from the default value of 10,000. However, this error affects all altimeter in the same way and is therefore negligible.
Transition from actual height to the flight surfaces
In the ground-level airspace is flown to actual height. For this, the altimeter must be adjusted each aircraft on the current meteorological air pressure of the imaginary sea level. This briefly described as QNH information is obtained from the nearest controlled airfield. The altimeter is always set before starting on QNH, at haul flights can be an adjustment required ( test flight in different weather and allow other pressure ratios).
Climb
The conversion of the altimeter of actual height (above QNH) at flight levels (above atmospheric pressure ) occurs during the climb when reaching the transition altitude (English transition altitude, TA). The transition altitude is 5000 feet MSL in Germany, but at least 2000 feet AGL. From here, the air traffic vertically after the semicircle Flight Rule (English semicircular rule ) is staggered in flight levels.
Descent
The descent is on reaching the transition levels (TRL; German uncommon transition surface, see also transition altitude ) of the reference air pressure switch again of 1013.25 hPa QNH. The TRL is set in Germany based on the current QNH:
- QNH 1013 hPa greater TRL → 60
- QNH 978-1013 hPa → TRL 70
- QNH less than or equal 977 → TRL 80
Designation of the flight surfaces
Flight surfaces are given as height in feet above the Standardisobaren of 1013.25 hPa. To simplify the specification is in Hektofuß. So corresponds to the flight level FL 60 (as would be indicated in the aeronautical ) an altitude of 6000 feet above the Standardisobaren.
- Instrument flyer (IFR ) use in Germany always around divisible by ten flight levels (FL (40 ), ( 50 ), ( 60), 70 to 350 ). Depending on the real pressure there FL 40, 50, 60 and 70 (for example from 977 hPa ) is not.
- VFR pilots ( VFR) use the 5 -ending flight levels (FL (45 ), ( 55), 65, 75, 85 and 95 ), where in ill -looking courses on the basis of 000 ° - 179 ° odd ( FL 55, 75, 95) be used and abused looking at courses on the basis of 180 ° -359 ° the straight flight levels (FL 45, 65, 85). See ICAO Annex 3 Appendix 2 and LuftVO § 31 para 2
Other countries may have different transition altitudes and thus may be less available flight levels. In the U.S. and Canada, for example, the transition altitude is determined by the beginning of class Alpha airspace at 18,000 feet, while the semi-circle rule applies regardless of it from 3000 feet above ground. Also called directional- dependent semi -circular cruising level are not the same internationally. So the UK used, for example, a quarter-circle system (English quadrantal rule ), while in Israel the Northern or Südrichtungen be distinguished (instead of east / west directions). Currently, a new worldwide standard is being developed.
Particularity
Depending on the weather conditions (temperature fluctuation ), as is apparent from the barometric formula, vary both the geometric altitude and the geometric distance between the flight levels. This does not appear in the altimeter. However, there are small differences that are insignificant for the flight practice. FL 60 corresponds independent of the geometric altitude always an air pressure of 812.8 hPa, which is indicated on the altimeter setting at a reference air pressure of 1013.25 hPa than 6000 feet altitude.
Further provisions
Flight surface on which a pilot wants to fly, must be included in the flight plan.