Aeronautical information is constantly changing: airspace structures and routes are revised, navigation aids change, SIDs and STARs are amended, runway and taxiway information changes. It is essential, for both efficiency and safety, that Pilots, Air Traffic Controllers, Air Traffic Flow Managers, Flight Management Systems and Aviation Charts all have the same information working from the same information base.
This can only be achieved by following the AIRAC system.
What is AIRAC?
AIRAC stands for Aeronautical Information Regulation And Control and steps from the Annex 15 - Aeronautical Information Services (AIS) document and defines a series of common dates and an associated standard aeronautical information publication procedure for States.
In short it defines that in all instances, information provided under the AIRAC system shall be distributed by the AIS unit at least 42 days in advance of the effective date with the objective of reaching recipients at least 28 days in advance of the effective date. Whenever major changes are planned and where additional notice is desirable and practicable, a publication date of at least 56 days in advance of the effective date should be used.
Three dates are to be remembered from this:
The two weeks between Publication date and Reception date is basically to allow for postal distribution.
The AIRAC cycle
The AIRAC cycle was adopted in 1964 and further improved over the years.
Key are the worldwide effective dates with 28 days intervals (e.g. 4 August 2005, 1 September 2005, 29 September 2005, ...). Effective days are always on a Thursday.
It may look indeed like a long period, 28 days, or even 56, but it should be understood that aeronautical information changes (mostly published through so called AIRAC Amendments) require:
Changes to local systems which includes interpreting, re-typing and re-coding the information.
Verification and Correction as publications are unfortunately seldom perfect.
Validation against other data; Flight Plans are just one example.
Re-distribution. Hereby think of Charts and Flight Management Systems to a fleet which can be anywhere in the world.
The AIRAC effective dates
The AIRAC effective dates are published in ICAO Doc 8126, the Aeronautical Information Services Manual, Table 2-1. Schedule of AIRAC effective dates'. They are also referred to in most national AIPs when providing the data delivery dates for data originators.
Schedule of AIRAC effective dates, 2015-2029
Each recipient has an internal date, called 'freeze' date or Cut-off date, before the effective date after which he can not accept changes anymore. For example, Aircraft Flight Management Systems need the data often 20 days before the effective date to allow for the information re-coding, information uploading and distribution.
Christmas and New Year
ICAO Annex 15 - Chapter 6 is clear: "The use of the date in the AIRAC cycle which occurs between 21 December and 17 January inclusive should be avoided as an effective date for the introduction of significant changes under the AIRAC system".
And in ICAO Doc 8126 – Chapter 4, because of reduced staffing and increased postal delays, "it is recommended that the AIRAC cycle date occurring in the 28-day period from 21 December to 17 January (both dates included) no longer be used as an AIRAC effective date for the introduction of significant operational changes. States experiencing similar problems during other holiday periods may wish to adopt a comparable system".