The International Civil Aviation Organization (ICAO) developed the Aeronautical Information Regulation and Control (AIRAC) system, which has associated with it a series of effective dates. These dates occur on Thursdays at 28-day intervals and ensure significant changes only take effect on the predetermined AIRAC effective date.

Charts do not always include an effective date, but they will always have an issue date. Again, charts that do not have an effective date are considered effective (usable) upon receipt. Charts that include an effective date should only be used on or after that date, and if you really want to be exact:

• FAA and Canada—Aeronautical information in the U.S., U.S. territories and Canada is generally effective on the designated effective date at 09:01 Coordinated Universal Time (UTC). The effective time applies to airspace, airways and flight procedures. It allows for implementation between 01:00 and 06:00 local standard time. Local authorities may change the date or time of implementation due to local operational considerations. Check NOTAMs and contact local ATC for information.

• International—ICAO guidance specifies that aeronautical information should be effective on the designated effective date at 00:00 UTC. However, national and local authorities often change the effective time to allow for implementation during the local night or at other times due to local operational considerations. When an effective time other than 00:00 UTC is used, ICAO requires that it be published in the official Aeronautical Information Publication (AIP) of the country. Check NOTAMs and contact local ATC for information.