TIME ZONES AND TIME
Time References Time is a critical factor in aviation. The entire industry revolves around accurate use of time. To eliminate confusion, the aviation industry uses Universal Coordinated Time (UTC) which is based on the 24 hour clock. Use of the 24 hour clock eliminates confusion and prevents mistaking A.M. for P.M. The conversion of time, expressed by the 24 hour clock, to Universal Coordinated Time (time in Greenwich, England) allows all aspects of aviation to operate on a standard time system no matter in what part of the world the flight is operating.
Universal Coordinated Time (UTC) - Zulu Time The time system, based on the 24 hour clock, which is the standard time used in all aviation operations, is called “Universal Coordinated Time” (UTC). Time zones are established by meridians or longitude; and the starting point is the zero degree meridian which passes through Greenwich, England. Known as: “GMT” for Greenwich Mean Time, or “Zulu” for the zero degree meridian. All these terms have now been replaced with the term “Universal Coordinated Time.” With the use of Universal Coordinated Time, flight crews know exactly when weather reports are valid anywhere in the world, Air Traffic Control knows exactly when aircraft are due at various destinations, and gov ernments know when you are entering or leaving their airspace.
Time Zones If we look down on the earth from above the North Pole, we would see a circle. By dividing the circle into 360 degrees, we establish lines which run from North to South, called meridians. The meridian which passes through Greenwich, England, is the zero degree meridian, or the “prime” meridian. Each 15 degrees establishes a time zone. (Note: 360 degrees divided by 15 equals 24; or 24 time zones, 24 hours.) However, the zones do not follow the meridians exactly. Local regulations many times dictate what time zone you are in. Some areas use DST, which can add confusion.
The 24 Hour Clock By designating the clock’s hour points from 0 - 24 instead of 1 - 12, we easily establish the 24 hour clock. Actually, the hour points are used twice on the 24 hour clock. The first time around the clock for A.M. hours, the second time around for P.M. hours. The 24 hour clock uses four digits to state the time. The first two digits state the hour, the last two express the minutes. Thus 5:00 AM be comes 0500 (expressed verbally: “Oh - Five - Hundred - Hours”). 5:15 AM becomes 0515.
Here are some additional examples: 10:00 AM becomes 1000 Noon becomes 1200 Midnight becomes 2400
5:00 PM becomes 1700 9:00 PM becomes 2100
Converting Local Time To UTC It is important to be able to convert your local time to UTC. Time zones are referred to by their local designation, such as Eastern, Central, Mountain, etc. Their reference to UTC is expressed as plus or minus “Zulu” (UTC). The Eastern time zone is “plus five,” or “plus four" during Daylight Savings Time: meaning, by adding 5 hours to local time, we convert it to UTC. During Daylight Savings, we add 4 hours to local to convert to UTC. Conversely, we subtract 5 hours (or 4 hours if Daylight Savings is in effect) to convert from UTC to local.
Remember, when converting to UTC, we must use the 24 hour clock for local time. Thus, 3:00 PM in New York converts to 1500 on the 24 hour clock. 1500 plus 5 becomes 2000 Universal Coor dinated Time.
Aviation Basics 12
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
