Area to be avoided
Area to be avoided or ATBA means a routing measure comprising an area within defined limits in which either navigation is particularly hazardous or it is exceptionally important to avoid casualties and should be avoided by all ships or certain classes of vessels. An ATBA may be either recommended or mandatory. An ATBA is recommendatory when ships are advised to navigate with caution in light of specially hazardous conditions. An ATBA is mandatory when navigation is prohibited or subject to a competent authority's conditions. ATBAs for deepwater ports are recommendatory.