L6 - Time25-11-2005 | |
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L6 - Time25-11-2005 | |
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1 - Zulu time (UTC) : As far as air traffic management is concerned, Co-ordinated Universal Time (UTC), also known as GMT (Greenwich Mean Time) or zulu, shall be used and shall be expressed in hours and minutes of the 24-hour day beginning at midnight. AM and PM indications shall not be used. PM hours shall be expressed from 12:00 to 23:59 (f.i. 03:12 PM = 15:12). Times are written as follows : - UTC (also called zulu times) => hh:mm z - local times => hh:mm loc The reason why zulu times are used is to avoid any confusion with local times which differ from one place to another at a given moment whereas the UTC time is the same everywhere at the same given moment. Thus, wherever you are, in Paris, Tokyo or Washington, if an aircraft takes-off at 12:00 z and land at 23:00 z, the flight time is quite easy to calculate : 11 hours. Now, if you consider the flight takes-off from Paris at 13:00 loc and land at Tokyo at 08:00 loc or at Washington at 18:00 loc, what is the flight time, mmm? Much more difficult without having the proper timezone table. 2 - Aeronautic night : The twilight ends in the evening when the center of the sun's disk is 6 degrees below the horizon and begins in the morning when the center of the sun's disk is 6 degrees below the horizon. As far as aeronautics is concerned, it is admitted that the night : - starts 30 minutes after sunset at laltitudes between 30° and 60° (15 mins between 0° and 30°). - ends 30 minutes before sunrise at laltitudes between 30° and 60° (15 mins between 0° and 30°). |
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