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FOMS Menu 145 (DST/GMT Deviations Program)

Daylight Savings Time is a popular concept all over the world. Unfortunately, it has yet to become a fixed standard; many countries or regions are still experimenting with the idea so time zones change from year to year. There is no universal period of application either, so a means of entering the applicable dates and deviations for each country is necessary. This program handles that function.

For each country, indicated by the appropriate ICAO country code, the program will store, for each standard time zone, the applicable DST deviation from GMT and the active dates for two DST periods; a current period and a future period. The program automatically checks on a weekly basis to see if any of the current periods are expiredIf they are, then the future period overwrites the current period and the records of all airports affected are updated accordingly, with a hardcopy listing being automatically generated to the system printer.

The modes available are:

  • Add

  • Edit

  • Delete

  • Video

  • Screen

  • Hardcopy

  • Quit

Add Mode



Country Code

Enter the one or two letter ICAO code for the country

If your entry is currently on file, the country name will be displayed as confirmation. If not, enter the appropriate name. 

The second IATA country code checks for international / domestic flights. The flight is considered domestic if the org/des/alc country codes have the same IATA as the 1st or 2nd IATA field. 

Note: The country code entered must be the ICAO code, not the IATA code. All system programs using information on the difference between local time and GMT look at the first letters of the ICAO airport code in order to find the appropriate data from this file. If you enter data using IATA codes, the system will not be able to find it.

Only for Apt

Select whether this is only to be used for reporting (i.e., it cannot be used in Apt/Apt), yes <Y> or no <N>.

Report Sid/Star

Options are Y, N, <D>CT. Select D to show DCT instead of SID/STAR. Blank is the same as Y.

Use DCT to Apt 

Options are Y, N or blank. The value in the field determines if DCT is displayed in ATC Item 15 when no SID/STAR is used for a given country. Blank defaults to Y.

Standard Deviation

Enter the standard deviation from GMT. Time zones in the Western hemisphere are behind GMT and are therefore negative. All entries must be in 15 minute increments. 

Example: For one hour enter <100>.


In one or two instances, there are regions within a particular time zone where two different DST deviations exist.

Example: Within the -600 zone in Canada one province has a one hour shift to DST while another has a two hour shift. This condition would be catered to by labeling one or the other an Exception. By entering an <E> in this field. 

Note: The program will not allow an Exception to exist unless a record for the given country/standard deviation already exists.

DST Deviation

Enter the difference between Local time and GMT that will apply while DST is in effect. In the Western hemisphere this is normally one hour less than standard. 

Example: In Canada, Eastern Standard time is -500, and the corresponding DST deviation is -400. 

Note: The program will not accept a DST deviation that shifts time in the wrong direction.

Current DST Period 

Enter the start and end dates/times of the current (or next) DST period using day, month (three letters), year and GMT time that the change takes effect.

If a future time period is known, it may be entered in the same manner. Enter only the periods during which DST is in effect; do not enter those periods when standard time applies. 

Once you have confirmed your entries, the program will check all airport files that may be affected and amend whatever records need to be updated.

Edit Mode

Enter the country code for the country you want to edit. The program will recall and display the zone with the least deviation

Under normal circumstances, an expired DST period will not exist on the system because of the weekly chronological test for period validity; all expired periods are automatically removed from the system and over-written by the future period information, if it exists. 

If you edit the current period, or add a new current period where none exists, the program will immediately update all applicable airport records and print a list of all such airports. A future period can only be added if a valid current period exists

Once a record has been edited the program will automatically call up the next standard deviation zone for the selected country being edited.

Delete Mode

Enter the ICAO country code and standard deviation of the record you want to delete. Before the program will delete an entry, it checks to see if any airports are going to be affected. If so, a report is generated and deletion will not take place until each such airport has been edited.

Video Mode

When you enter a country code in the Video mode, the program automatically calls up and displays the record for the first standard deviation zone on file for the country. You may then filter through all of the zones available for the given country, as well as any preceding or subsequent record. by using the down arrow or the up arrow as the case may be. Pressing <Enter> will clear the screen; pressing <Enter> a second time will return you to the command line.

Screen Mode

When the Screen mode is selected you will be presented with a range selection screen which will permit you to enter the range of country codes you want to review; the default values are A and Z. For each country code, the country name, standard time zones, their DST deviations. and current and future active periods are displayed.

Hardcopy Mode

The Hardcopy mode will produce the same reports as the Screen mode except that the output will be sent to the system printer.

Quit Mode

Entering <Q> from the command line will immediately return you to the previous program selection menu.

Note: The following descriptions represent the typical access and privileges afforded to users designated as Dispatch Managers/Supervisors. Users with dispatcher privileges will have limited access to a subset of the screens presented.

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