FCC GMDSS common mistakes
FCC GMDSS · Understand the traps and how to avoid them.
When sending a DSC distress alert, the candidate selects the correct distress nature (e.g., 'Fire') but then fails to select the correct subsequent communication method (e.g., radiotelephony on Ch 16) before transmitting, or omits the distress alert entirely and goes straight to a voice MAYDAY on Ch 16.
Candidates conflate the DSC alert with the follow-on voice distress call. They memorize the MAYDAY script but forget that the DSC alert is a separate, mandatory step that must specify the follow-on communication mode. Under stress, they skip the alert or misconfigure the follow-on.
What to do instead
Practice the two-step sequence until automatic: first, on the DSC controller, select 'Distress' then the nature of distress, then the follow-on communication (typically 'Radiotelephony' and the suggested channel, often Ch 16), then press and hold the distress button for 5 seconds. Only after the alert is transmitted (or if time is critical and the alert fails) send the voice MAYDAY. Use a checklist that explicitly separates 'DSC alert' from 'voice MAYDAY'.
The candidate sends a DSC distress alert and then, without waiting for an acknowledgement, immediately sends a second distress alert or a distress priority Inmarsat call, or cancels the alert prematurely.
Candidates are anxious about getting a response and do not understand the acknowledgement protocol: a DSC distress alert is typically acknowledged by a coast station via DSC (or by a ship via DSC if no coast station responds within 5 minutes). Sending multiple alerts causes confusion and may be considered a false alert.
What to do instead
Memorize the acknowledgement timing: wait at least 5 minutes for a DSC acknowledgement. If none is received, a distress alert may be retransmitted or a distress call made on radiotelephony. Only cancel a distress alert if it was transmitted in error, using the proper 'distress alert cancellation' procedure on DSC and voice. Practice scenarios with timers to internalize the wait.
The candidate incorrectly identifies the sea area (A1, A2, A3, A4) for a given vessel equipment configuration, or misstates which GMDSS equipment is mandatory for each area.
Candidates memorize definitions in isolation but cannot apply them to a practical scenario. They confuse A2 (MF coast station coverage) with A3 (Inmarsat coverage) or forget that A4 requires HF and has no Inmarsat coverage.
What to do instead
Build a table from memory: A1 = VHF DSC + Ch 70 + suitable shore coverage; A2 = A1 plus MF DSC (2187.5 kHz) and MF radiotelephony; A3 = A1/A2 plus Inmarsat (or HF) and enhanced group calling; A4 = all plus HF DSC and HF radiotelephony/telex. For each area, list the mandatory equipment and the distress alerting methods. Test yourself with vessel route scenarios (e.g., 'A ship transits from A1 to A3; what must it carry?').
The candidate uses the wrong DSC frequency or channel for the intended purpose: sending a distress alert on a non-distress DSC frequency, or using Ch 70 for routine calling, or confusing the MF/HF DSC distress frequencies (2187.5 kHz, 8414.5 kHz, etc.) with the radiotelephony distress frequencies.
Candidates mix up the many frequencies and channels. They remember 'Ch 70 is for DSC' but forget it is exclusively for distress, urgency, and safety, not routine. They also confuse the MF/HF DSC distress frequencies with the corresponding radiotelephony frequencies.
What to do instead
Create a frequency map: VHF Ch 70 (156.525 MHz) = DSC only, no voice; MF 2187.5 kHz = DSC distress; HF 4207.5, 6312, 8414.5, 12577, 16804.5 kHz = DSC distress. Radiotelephony: VHF Ch 16 (156.8 MHz), MF 2182 kHz, HF 4125, 6215, 8291, 12290, 16420 kHz. Drill with flashcards until you can state the purpose of each frequency without hesitation.
The candidate fails to correctly set up or interpret a DSC routine call: they omit the proposed working channel, or they send a routine call on a distress frequency, or they do not properly acknowledge a routine DSC call.
Candidates focus on distress DSC and neglect routine DSC procedures. They may not know that a routine call must include the proposed working channel (e.g., Ch 72) and that the acknowledgement should be sent on DSC before switching to the working channel.
What to do instead
Learn the routine DSC call format: select the station's MMSI, choose 'Routine' priority, specify the working channel (e.g., Ch 72 for ship-to-ship, or a duplex channel for ship-to-shore), and send. The receiving station acknowledges via DSC, then both switch to the working channel. Practice with a simulated DSC controller or a software trainer, ensuring you never use Ch 70 for routine.
The candidate cannot correctly identify the Inmarsat ocean region for a given geographical position, or incorrectly uses the Inmarsat system for distress alerting when the vessel is in A4 (outside Inmarsat coverage).
Candidates memorize ocean region names but not their boundaries. They also assume Inmarsat covers the entire globe, forgetting the polar regions (A4) where only HF is available.
What to do instead
Study an Inmarsat coverage map: Atlantic Ocean Region (AOR) East and West, Indian Ocean Region (IOR), Pacific Ocean Region (POR). Know approximate boundaries (e.g., AOR-W covers the Atlantic west of 0° longitude to about 100°W; AOR-E covers from about 100°W to 70°E; IOR from 70°E to 180°E; POR from 180°E to 100°W). For A4, remember that Inmarsat geostationary satellites do not cover above about 76°N/S, so HF DSC/MF/HF radiotelephony is required. Use a globe or chart to practice locating positions.
The candidate does not know the correct procedure for receiving Maritime Safety Information (MSI) via Inmarsat Enhanced Group Call (EGC) or NAVTEX, or fails to distinguish between SafetyNET (Inmarsat) and NAVTEX (MF) coverage and message types.
Candidates often treat MSI as background reading and do not grasp the operational differences: NAVTEX is local (up to 200 nm) on 518 kHz (international) and 490/4209.5 kHz (national), while SafetyNET is global via Inmarsat. They also forget that EGC can be used for distress-related messages and that NAVTEX has specific message categories (A, B, D, etc.).
What to do instead
Make a comparison table: NAVTEX (518 kHz international, 490 kHz national, 4209.5 kHz tropical) covers coastal waters; SafetyNET via Inmarsat covers A3 (and A2/A1 if equipped). Learn the NAVTEX message categories (A = navigational warnings, B = meteorological warnings, D = search and rescue, etc.) and the EGC message types (SafetyNET for MSI, FleetNET for commercial). Practice identifying which system to use for a given position and message type.
When transmitting a MAYDAY or PAN-PAN on radiotelephony, the candidate omits essential elements such as the vessel's position, nature of distress, or number of persons on board, or uses the wrong priority (e.g., PAN-PAN for a life-threatening situation).
Candidates memorize the sequence but under exam pressure they skip items. They also confuse the criteria for MAYDAY (grave and imminent danger) versus PAN-PAN (urgency, no immediate danger).
What to do instead
Use the mnemonic 'MIPDANIO' for MAYDAY: Mayday (x3), This is (vessel name/callsign x3), MMSI, Position, Nature of distress, Assistance required, Number of persons on board, Other information (e.g., weather, raft). For PAN-PAN, the same structure but with 'Pan-Pan' and the nature of urgency. Practice aloud with a timer, ensuring all elements are included in under 30 seconds. Review scenarios to distinguish MAYDAY from PAN-PAN.
The candidate misstates FCC licensing requirements: e.g., believes a ship station license is not required for a recreational vessel with a VHF radio, or does not know the requirement for a Restricted Radiotelephone Operator Permit (RP) or the GMDSS Radio Operator License for certain vessels.
Candidates confuse the types of licenses and which vessels need them. They may not know that any vessel with a radio transmitter (including VHF) must have a ship station license, or that operators of GMDSS-equipped vessels need a GMDSS Radio Operator License (or a GMDSS Radio Maintainer License for maintenance).
What to do instead
Memorize the FCC rules: every ship with a radio transmitter requires a ship station license (47 CFR Part 80). Operators must hold a Restricted Radiotelephone Operator Permit (RP) for non-GMDSS vessels, or a GMDSS Radio Operator License for GMDSS vessels. The license term is 10 years for ship station licenses. Use the FCC website or study guides to confirm current requirements, and create a checklist for different vessel types.
The candidate fails to follow the correct distress alert relay or distress traffic handling procedures: e.g., a ship not in distress transmits a MAYDAY relay without the proper 'MAYDAY RELAY' prefix, or does not maintain a listening watch on the distress frequency after acknowledging.
Candidates learn the basic MAYDAY but not the relay procedure or the associated silence periods. They may also forget that a station acknowledging a distress alert must maintain a continuous watch on the associated radiotelephony frequency.
What to do instead
Learn the MAYDAY RELAY format: 'MAYDAY RELAY' (x3), 'This is' (vessel name/callsign x3), MMSI, followed by the original MAYDAY message details. Understand that a relay is only sent when the distressed vessel cannot communicate or when a coast station requests it. After acknowledging, keep a listening watch on the distress frequency (e.g., Ch 16 or 2182 kHz) and do not transmit unless assisting. Practice with role-play scenarios.