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FCC GMDSS: Satellite Communications (Inmarsat) and MSI Reception

FCC GMDSS · Work through your exam, one topic at a time.

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Satellite Communications (Inmarsat) and MSI Reception

What this domain tests

This domain tests the satellite side of GMDSS - what each Inmarsat service does, how a distress alert reaches an RCC, and how maritime safety information is received in each sea area.

Inmarsat in GMDSS

Inmarsat operates geostationary satellites over four ocean regions (Atlantic East, Atlantic West, Indian, Pacific), covering about 70°N to 70°S - the A3 band. GMDSS services:

  • Inmarsat-C - store-and-forward messaging, no voice, with a dedicated distress button, EGC reception and position reporting.
  • Fleet / FleetBroadband - voice and data with selectable priority (distress, urgency, safety, routine); distress priority pre-empts other traffic at the land earth station, which routes the call to an RCC.
  • SafetyNET (EGC) - enhanced group call broadcasts of MSI to fixed areas or groups of ships.

A satellite distress alert is followed by a distress message with the usual content: identity, position, nature of distress, assistance required, persons on board.

MSI reception

MSI covers navigational warnings (NAVAREAs), meteorological warnings and forecasts (METAREAs), SAR information, ice, piracy and other urgent information. Carriage: NAVTEX on 518 kHz (international, English only; 490 kHz national, 4209.5 kHz tropical) for coastal waters, typically 200–400 nm; SafetyNET/EGC for A3; HF NBDP broadcasts for A4. NAVTEX messages carry a station letter, a subject indicator (A navigational warning, B meteorological warning, C ice, D SAR, E forecast), a two-digit serial and time, and a receiver must be able to receive indicators A, B and D.

Worked example

A ship in mid-Indian Ocean (A3) needs MSI. Reasoning: NAVTEX is out of range, so the EGC/SafetyNET receiver is the source; it must be tuned to the Inmarsat region covering the ship's position, and the operator should confirm that navigational and meteorological message types are not filtered out. A distress relayed on SafetyNET would then be worked by radiotelephony on the frequency given.

Traps

Expecting Inmarsat-C to carry voice; assuming satellite coverage reaches A4; confusing NAVTEX 518 kHz with 490 kHz (national language) or 4209.5 kHz; treating SafetyNET as a NAVTEX function; forgetting that 406 MHz EPIRB alerting is separate from the satellite terminal and that the EPIRB must be registered with the national authority (NOAA in the US).