Technical Circular No:28/2018

Subject: Migration of INMARSAT I-3 to I-4 Services.

 PDF file Download PDF 

  • The Inmarsat-3 (I-3) constellation of satellites are reaching the end of its lifespan, which has made it necessary for Inmarsat to roll out the end of life process for several of their legacy services and to migrate those services that will continue (including Inmarsat- C) on to the Inmarsat-4 (I-4) constellation of satellites.
  • The transition of services from the I-3 to I-4 constellation will be implemented in four phases and will take approximately nine months to complete as per the below schedule.

I-3 to I-4 migration



Atlantic Ocean Region West (AOR-W) I-3 to Americas (AMER) I-4

Fleet 77, Swift 64 and Classic Aero services -  30 April 2018 at 17:30 UTC

Inmarsat C (to include Aero C and Mini C) services – 09 May 2018 at 14:00 UTC

Pacific Ocean Region (POR) I-3 to Asia/Pacific (APAC) I-4

End Q2 2018

Atlantic Ocean Region East (AORE) I-3 F2 moved to I-3 F5

End Q3 2018

Indian Ocean Region (IOR) I-3 to Alphasat EMEA I-4

End Q4 2018


  • Due to the migration from I-3 to I-4 satellites, the coverage areas will change and users will need to ensure that their devices are pointed to the relevant satellite. This process will generally be managed automatically by the terminal without the need for user intervention. However, in some instances, users will need to manually repoint their devices to the appropriate satellite.
  • The existing and new satellite coverage maps are shown in the below figure.

  • The migration applies to all users of Inmarsat C (Standard C and Mini C), and will affect the polling and data reporting services.
  • During the migration process, it is likely that many poll commands will be sent, thus flooding the system with messages which will be put in a queue. As a result, Providers expect delays during this period.
  • Also a short interruption of service may be experienced. All messages ‘To-mobile station’ will continue to be accepted by the Land Earth Station (LES) and will be queued for delivery after the migration. ‘From-mobile station’ messages will be queued on the terminal and will be delivered once the terminal re-establishes communications with the satellite.
  • For smooth transition, ship owners and Masters are advised to be guided by below recommendations:
  • Inmarsat C devices to be switched to an adjacent Ocean Region before each migration. Switching devices in advance will make the migration smoother and will avoid possible outage in tracking operations. Before Phase #1, switch devices located between 240 E and 200 W to AORE.
  • Control the Ocean Regions where their LRIT DNID(s) has been downloaded in the past. If a DNID is available in the 4 Ocean Regions, the migration has no effect on position/data reporting.


  • Nil


This Technical Circular and the material contained in it is provided only for the purpose of supplying current information to the reader and not as an advice to be relied upon by any person. While we have taken utmost care to be as factual as possible, readers/ users are advised to verify the exact text and content of the Regulation from the original source/ issuing Authority.

PDF file Download PDF



All Technical Circulars