什麼是flight level

飛行高度(Flight Level):

Flight Level is a standard nominal altitude of an aircraft,referenced to a world-wide fixed pressure datum. It is not necessarily the same as the aircraft's true altitude above mean sea level.

Flight Level是指飛行高度，簡寫是FL。

飛行高度，故名思義是飛機飛行時的高度，一般是使用尺(feet)為單位，但有部份國家如中國及俄羅斯均使用米(metre)為單位。

由於飛機是用氣壓計來計算飛行高度，要準確知道飛機身處的高度時便要知道飛機身處的空域的氣壓(Area QNH)，但因為氣壓會經常改變及飛機在高空飛行時一般的速度較高，相對地經過某一地區的時間較短，為免要經常調較高度計及避免危險，在某一地區當飛機經過過渡性高度(Transition Altitude, TA)時機師需將高度計的設定氣壓改為標準大氣平均值(International Standard Atmosphere, ISA)的29.92inHg或1013mbar。而TA的數值是因地區而異，如在英國地區是會在3,000尺至7,000尺之間，在美加地區則一律是18,000尺。當飛機標示自己的飛行高度時會先用FL作為前頭，而高度則會以實際高度減去最後兩個位來標明，舉例來說如果飛機在35,000尺時飛行高度會是FL350。而當使用QNH的高度值時會以實際高度來標示，如在美加地區8,500尺時會標為8,500ft而不會是FL85。

it is the height of how high the plane should be flying. if they dont follow the flight level, then it will be misleading to the air traffic controller.

Flight level is the height that the aircraft is flying at... Usually if its FL390 it would means the aircraft is flying at a height of 39000m...
The reason why flight level occur is that on every flight path, it is likely that there would be more than 1 aircraft flying on the same path... And to avoid any collision, it have a flight level at which the local control tower will tell the aircraft to fly at as the local control tower will have the understanding of how many aircraft are at the same path...
Usually, aircraft would be flying at a different height while they are flying at a different direct to avoil any collision occuring...
By introducing Flight Level, it made it easier while the aircraft is in contact with the control tower... And also the differ the flight level for flights flying on the same path but opposite direction to avoid air collision...

飛行高度(Flight Level):
是一個飛行限制的高度，萬一高於或低於這個飛行高度，飛機可能會有危險！