To know about these two, we first need to know what is AIO. Below is a brief description outlining the definition of AIO.
AIO
ADMIRALTY Information Overlay (AIO) is a worldwide digital dataset that is designed to be displayed over ENCs in ECDIS and other chart display systems to provide additional information during passage planning. AIO contains Temporary and Preliminary Notices to Mariners (T&P NMs) and Extra Preliminary Notices to Mariners (EP NMs) that highlight the differences between ENCs and paper charts. ADMIRALTY Information Overlay also draws attention to areas where there is no ADMIRALTY chart at equivalent scale to the ENC, indicated by ‘No Overlay’ polygons. AIO is updated weekly and is available for free for AVCS users.
Know More About ADMIRALTY Information Overlay : AIO: Enhance Your Passage Planning with ADMIRALTY Information Overlay
How to obtain EP NMs and T & P NMs
EP NMs updates come with weekly ECDIS updates and are plotted on ECDIS automatically. T & P NMs are broadcasted by ADMIRALTY every week and are also plotted automatically on ECDIS along with the weekly. The only difference is that T & P NMs need to be verified by 2nd officer every week once the list is broadcasted by the ADMIRALTY. Some countries do not incorporate these into ECDIS as AIO. They straight away update their respective ENCs. Hence, T & P NMs must be verified for this. The ones that have not been updated as AIO or ENCs, those need to be plotted manually. This happens occasionally but most of the T & P NMs are auto-plotted in the ECDIS with weekly update.
Now that we are briefed about an AIO. Lets see what are T & P notices to mariners.
T & P ( Temporary & Preliminary Notices to Mariners)
A Preliminary notice (P-notice) means an activity or condition that will become permanent and will result in a chart revision. Example: Dredging, making of a breakwater, installation of a buoy, etc. A P-notice will always be followed later by a notice of effect. A Temporary notice (T-notice) means conditions that will not become permanent. Example: Mining activity, firing practice areas, etc.
Temporary and Preliminary Notices are issued by Hydrographic Offices when the information will only be valid for a short period of time or needs to be promulgated quickly and a normal chart correction would take too long to prepare and distribute. A T & P polygon will contain a number with T or P in the middle. Example: 123(T)/24 or 456(P)/24.
EP (ENC Preliminary) NMs
EP NMs, ENC Preliminary (EP) NMs include information on reported hazards to navigation, which have been incorporated into the Admiralty paper chart but not yet in the appropriate ENC. These NMs are displayed in the same way as T&P NMs, as a polygon with a hatched fill which indicates the area affected by the NM. Each NM is allocated a unique EP NM number and is exclusive to AIO. An EP NM polygon will contain a number starting with EP. Example: EP 1234/24.
