FCC GMDSS cheat sheet

MAYDAY (spoken) = distress; distress is defined as a grave and imminent danger requiring immediate assistance. Only a person in authority on the vessel may authorize transmission.

Distress call format on radiotelephony: MAYDAY (x3), THIS IS, vessel name/call sign (x3), MAYDAY, name/call sign, position, nature of distress, assistance required, persons on board, any other information.

MAYDAY RELAY (x3) is used by a station not itself in distress to relay a distress message; a coast station or ship may relay when the original station cannot transmit.

PAN PAN (x3) = urgency: concerning the safety of a vessel or person but not immediate grave danger (e.g., man overboard with recovery underway, serious illness, disabled vessel not in immediate danger).

SECURITE (x3) = safety: navigational or meteorological warnings, or important safety information.

Silence periods: radiotelephony 00 and 30 minutes past each hour on 2182 kHz (MF); on VHF Ch 16, no fixed silence period is required under GMDSS but Ch 16 is the distress/safety/calling channel and must be monitored.

On receipt of a distress alert: acknowledge only if you are in a position to assist, or if no other station has acknowledged; do not acknowledge DSC distress alerts on behalf of a coast station.

Cancel false distress: transmit MAYDAY (or appropriate) cancellation on the same frequency, addressing ALL STATIONS, identifying yourself and stating the alert was inadvertent and cancelled.

Distress traffic has absolute priority over all other transmissions; all stations hearing it must cease transmissions capable of interfering and continue to monitor.

Sea Area A1: within VHF coverage of at least one coast station with continuous DSC alerting (approx. 20-30 nm); minimum fit includes VHF DSC, VHF radiotelephony, SART (2), EPIRB, and NAVTEX or HF MSI receiver.

Sea Area A2: beyond A1 but within MF coverage of at least one coast station with continuous DSC alerting (approx. 100-150 nm); requires MF/HF DSC plus the A1 equipment.

Sea Area A3: beyond A1 and A2, within coverage of an Inmarsat geostationary satellite with continuous alerting (approx. 70°N to 70°S); requires an Inmarsat ship earth station or HF DSC.

Sea Area A4: remaining sea areas outside A1, A2 and A3 (polar regions); requires HF DSC and HF radiotelephony plus the A1-A3 equipment.

Functional requirements: distress alerting, distress alert reception, distress communications, SAR coordinating communications, on-scene communications, locating signals, MSI reception, and bridge-to-bridge communications.

GMDSS equipment carriage is specified by vessel type and sea area under SOLAS Chapter IV; FCC licenses the radio station and operator, SOLAS sets the equipment fit.

EPIRB: 406 MHz COSPAS-SARSAT transmits to satellites; 121.5 MHz is a homing frequency for SAR aircraft. EPIRB must be float-free and automatically activated, or manually activated.

SART: 9 GHz (X-band) radar transponder, range approximately 5-10 nm depending on radar height; responds with a series of dots on the rescuing vessel's radar display.

DSC distress alert uses the dedicated distress button; it transmits on VHF Ch 70, MF 2187.5 kHz, or HF 4207.5/6312/8414.5/12577/16804.5 kHz.

DSC distress alert content: vessel MMSI, nature of distress (fire, flooding, collision, grounding, listing, sinking, disabled, abandoning, piracy, man overboard, EPIRB), position, time, and communication mode (radiotelephony preferred).

VHF Ch 70 is DSC-only; voice communications must move to Ch 16 (or a working channel) after the DSC exchange.

DSC distress alert is normally followed by a distress message on radiotelephony (or NBDP) on the associated frequency: Ch 16 for VHF, 2182 kHz for MF, or the paired HF channel.

Individual routine DSC call: select the station's MMSI, choose the working channel, transmit; the called station acknowledges on DSC, then both switch to the working channel for voice.

Distress alert acknowledgement by a coast station or ship is sent on DSC with the distress priority and typically includes the acknowledging station's MMSI.

A DSC distress alert should not be retransmitted if it has been acknowledged; if unacknowledged after a reasonable interval, the station may retransmit or escalate to voice MAYDAY.

DSC self-identification: ship MMSI is 9 digits; coast station MMSI begins with 00; group MMSI begins with 0; SAR aircraft begin with 111.

Inmarsat provides geostationary satellite coverage between approximately 70°N and 70°S; it does not cover polar regions (Sea Area A4).

Inmarsat-C is a store-and-forward messaging terminal used for distress alerting (via the Inmarsat distress button) and for receiving Enhanced Group Call (EGC) SafetyNET messages.

SafetyNET is the Inmarsat EGC service that broadcasts MSI (navigational and meteorological warnings, SAR information) to defined sea areas; reception requires the terminal to be logged in and the appropriate area selected.

NAVTEX: 518 kHz international (English), 490 kHz national, 4209.5 kHz for tropical/coastal areas; broadcasts typically on a 10-minute schedule with 518 kHz as the primary international frequency.

NAVTEX message types: A navigational warning, B meteorological warning, C ice report, D SAR information, E meteorological forecast, F pilot service, G AIS, H LORAN, I reserved, J SATNAV, K other, L AIS (additional), V-V special, Z no message.

NAVTEX receiver should be set to receive 518 kHz continuously and to the appropriate transmitter coverage area; stations are identified by a letter (A-Z) designating the NAVTEX transmitting station.

SafetyNET EGC messages include navigational warnings, meteorological warnings, SAR messages, and piracy warnings; a ship's EGC receiver must be configured for the correct ocean region and area.

Inmarsat-C distress alert is initiated by pressing the distress button (protected by a cover); the alert includes position, nature of distress, and ship's identity, and is routed to an RCC.

Radiotelephony frequencies: VHF Ch 16 = 156.800 MHz (distress/safety/calling); Ch 70 = 156.525 MHz (DSC only); Ch 13 = 156.650 MHz (bridge-to-bridge, one watt).

MF/HF radiotelephony: 2182 kHz distress/safety; HF distress/safety frequencies include 4125, 6215, 8291, 12290, 16420 kHz.

NBDP (narrow-band direct printing) is used for telex over radio, primarily on HF; distress telex uses 2174.5 kHz (MF) and 4177.5, 6268, 8376.5, 12520, 16695 kHz (HF).

NBDP distress procedure: select the distress frequency, use the ARQ or FEC mode as appropriate, and transmit the distress message in the standard telex format (distress signal, identity, position, nature, assistance required).

ARQ (Automatic Repetition reQuest) is a two-way error-correcting mode used between two stations; FEC (Forward Error Correction) is a one-way broadcast mode used for transmitting to multiple stations (e.g., MSI, navigational warnings).

Radiotelephony phonetic alphabet: Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.

Standard replies: ROGER (received), WILCO (will comply), OVER (invitation to reply), OUT (end of exchange, no reply expected).

DSC and NBDP are distinct: DSC is a digital alerting/calling system; NBDP is a text messaging system used for telex and MSI; both are part of GMDSS but serve different functions.

FCC Part 80 governs maritime radio services; the ship radio station license is required for vessels subject to SOLAS or carrying GMDSS equipment, and for voluntary vessels using certain frequencies.

GMDSS operator certificates: the GMDSS Radio Operator's License (no Morse code required) and the GMDSS Maintainer's License; the Restricted Radiotelephone Operator Permit is for non-GMDSS vessels.

The ship station license and operator license must be available on board; the license shows the vessel's call sign and MMSI.

MMSI is assigned by the FCC (or a delegated authority) and must be programmed into DSC and AIS equipment; it is not the same as the call sign.

Distress, urgency and safety communications are exempt from the normal requirement to identify with call sign, but stations must still identify appropriately during the exchange.

FCC rules prohibit false distress signals; transmitting a false distress alert is a serious violation subject to penalties and may require cancellation procedures.

The Radio Regulations (ITU) define the distress, urgency and safety frequencies and the silence periods; FCC Part 80 incorporates these by reference.

Vessel radio station inspections: FCC may inspect; GMDSS equipment must be maintained and tested per the applicable SOLAS and FCC requirements, with records kept.