The navigational assistance service is especially important in difficult navigational or meteorological circumstances or in case of defects or deficiencies. This service is normally rendered at the request of a vessel or by the VTS when deemed necessary.

Source documents:

1. Approval e-Navigation Strategic Implementation Plan (doc. MSC 85/26) 2014
2. Proposal e-Navigation Strategic Implementation Plan (MSC 85/26/Add.1) 2014