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Figure 2.6. Meridians and parallels – the basis of measuring time,

distance and direction

The standard practice is to establish a time zone for each 15½ of

longitude. This makes a difference of exactly 1 hour between each
zone.
In most aviation operations, time is expressed in terms of the 24-
hour clock. Air traffic control instructions, weather reports and

broadcasts, and estimated times of arrival are all ________on this
system. For example: 9 a.m. is expressed as 0900; 1 p.m. is 1300; 10
p.m. is 2200 etc.

Because a pilot may cross several time zones during a flight,
___________has been adopted. It is called Universal Coordinated
Time (UTC) and is often referred to as Zulu time. UTC is the time at

the 0½ line of longitude which passes through Greenwich, England.
All of the time zones around the world are based on this reference. To
convert to this time, a pilot should do the following:

• Eastern Standard Time Add 5 hours
• Central Standard Time Add 6 hours
• Mountain Standard Time Add 7 hours
• Pacific Standard Time Add 8 hours

For daylight saving time, 1 hour should be subtracted from the
calculated times.
Some higher latitude countries use daylight saving time for part of

the year, typically by changing clocks by an hour. Many
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