Coast Guard issues safety alert on AIS text messaging, accuracy

The following is a marine safety alert issued by the U.S. Coast Guard:
Safety Alert 05-10


Automatic Identification System (AIS) is an internationally adopted radio-navigation protocol to exchange pertinent navigation-related information amongst its users, either afloat, ashore or airborne. AIS facilitates vessel traffic management while simultaneously reducing the need for voice radiotelephone transmissions. AIS provide vessel information, including the vessel’s identity, type, position, course, speed, navigational status and other safety-related information. It receives automatically such information from similarly fitted ships; monitors and tracks ships; and exchanges data with shore-based facilities.

Usage During Navigation – AIS enhances user’s situational awareness, and can mitigate risk of collision by providing vessels with more reliable information upon which to base their passing arrangements. This can be accomplished via an AIS safety related text message of up to 156 characters long. However, the Coast Guard strongly reminds operators that use of AIS text messaging does not relieve the vessel of other requirements, such as the Vessel Bridge-to-Bridge Radiotelephone regulations or of the requirements to sound whistle signals and display lights or shapes in accordance with the International or Inland Navigation Rules.

Usage During Emergencies – With respect to using AIS safety related text messages in emergency situations, users must be aware that they may not be received, recognized or acted upon as Global Maritime Distress Safety Systems (GMDSS) messages would be by the Coast Guard, other competent authorities or maritime first responders. Thus AIS must not be relied upon as the primary means for broadcasting distress or urgent communications, nor used in lieu of GMDSS such as Digital Selective Calling radios which are designed to process distress messaging. Nonetheless, AIS remains an effective means to augment GMDSS and provides the added benefit of being ‘seen’ (on radar or chart displays), in addition to being ‘heard’ (via text messaging) by other AIS users within VHF radio range.

Operators Must Ensure Accurate Data -The Coast Guard has noted a high percentage of inaccurate and improper AIS messaging data. AIS requires operators to routinely update their data as it relates to navigation status, draft, origination and destination ports, and eta. Other pertinent static data is to be maintained accurately. Dynamic Data, such as that from positioning sources like GPS via external sensors must always be operational, accurate and continuously updated. See for additional details. AIS is only as good as the information provided and exchanged, therefore, users must ensure their unit is always in effective operating condition and broadcasting accurate information.

This safety alert is provided for informational purposes only and does not relieve any domestic or international safety, operational or material requirement. Please visit for further information on AIS or on how to program and properly use AIS messaging. Developed by the Office of Waterways Management, U. S. Coast Guard Headquarters, Washington, D.C.,

By Professional Mariner Staff