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What is the ADMIRALTY Information Overlay (AIO)?

Updated: Nov 13, 2020

The ADMIRALTY Information Overlay (AIO) contains additional information which is considered navigationally significant and can be used in conjunction with ENCs to identify areas of possible uncertainty and risk during passage planning.

The Overlay contains all ADMIRALTY T&P NMs in force worldwide and navigationally significant differences between ENCs and ADMIRALTY paper charts, published as ENC Preliminary NMS (EP NMs).

Areas, where UKHO does not publish ADMIRALTY T&P NMs, are highlighted with a No Overlay feature and other sources of information, including national T&P NMs, should be consulted.

ATO IS an aid to navigators during planning ENC's remain the official charts that should be used, for navigation and may include information in their ENCS I VNFO folder on AVCS discs T&P NM information. A list of ENC producers that include T&P NM available on the UKHO website at and In the /INFO folder on AVCS discs.

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