Distinguish between MAYDAY, PAN PAN, and SECURITE. Give an example of when each would be used.

A. GMDSS SIGNAL PRIORITIES — THREE LEVELS: (1) MAYDAY (DISTRESS): gravest and most immediate threat to life or vessel. Used when: the vessel is sinking; a person is in the water in immediate danger; fire out of control; flooding that will sink the vessel. FORMAT: "MAYDAY MAYDAY MAYDAY" repeated three times. PRIORITY: highest — all other communications must cease; (2) PAN PAN (URGENCY): serious situation but not immediately life-threatening. Used when: a person is injured and medical advice is urgently needed; a vessel is in difficulty but not yet in immediate danger (e.g., engine failure but anchored safely, or disabled but under tow); a person is overboard and has been in water a short time; an urgent navigational warning affecting other vessels. FORMAT: "PAN PAN PAN PAN PAN PAN" repeated three times. Priority below MAYDAY; (3) SECURITE (SAFETY): safety message — important navigational or meteorological information. Used when: broadcasting a navigational hazard warning (ice, wreck, buoy off station); transmitting a weather warning; a vessel is transmitting its approach to a narrow channel or canal. FORMAT: "SECURITE SECURITE SECURITE" — repeated three times. Example: "SECURITE — all stations — be advised large piece of floating container debris at position [lat/lon]." Transmitted on Ch 16 after announcing on the working channel. SAFETY priority: broadcast by coast guards, pilots, and vessels.

B. PAN PAN and SECURITE are both distress signals with equal priority. MAYDAY is used for vessel distress, PAN PAN and SECURITE are used for crew distress.

C. SECURITE is used instead of MAYDAY when the distress is not yet confirmed. Once a distress is confirmed, upgrade to MAYDAY. SECURITE and PAN PAN have the same meaning.

D. MAYDAY can only be broadcast by the master. OOWs may use PAN PAN and SECURITE but must obtain master authority before transmitting MAYDAY.

A. DSC DISTRESS ALERT — VHF PROCEDURE: DSC (Digital Selective Calling) on VHF Channel 70 is the primary GMDSS distress alerting mechanism. PROCEDURE: (1) ENSURE POSITION IS UPDATED: the DSC controller must have a current GPS position input (most modern sets auto-update from GPS). Verify the position shown is current; (2) OPEN THE DSC CONTROLLER: navigate to the distress function — typically a protected button (lift cover or press and hold to prevent accidental activation); (3) SELECT NATURE OF DISTRESS: most DSC controllers allow selection of distress nature — UNDESIGNATED, FIRE, FLOODING, COLLISION, GROUNDING, LISTING, SINKING, DISABLED AND ADRIFT, ABANDONING SHIP. If time permits, select the correct nature; (4) TRANSMIT: press/hold the distress button for the required duration (typically 5 seconds with button confirmation). The controller transmits the DSC distress call on Ch 70 — this broadcasts your MMSI, position, time, nature of distress to all vessels in range and to coast stations; (5) SWITCH TO CH 16: immediately after DSC transmission, switch VHF to Ch 16 and transmit the voice MAYDAY message; (6) MAYDAY VOICE: "MAYDAY MAYDAY MAYDAY — THIS IS [vessel name × 3] — MAYDAY [vessel name] — POSITION [lat/lon] — [NATURE OF DISTRESS] — [POB] — [ANY OTHER RELEVANT INFO] — OVER"; (7) AWAIT ACKNOWLEDGEMENT: coast stations and vessels will acknowledge on Ch 16.

B. The DSC distress alert is transmitted on Ch 16. Tune the VHF to Ch 16, press the distress button, and speak the MAYDAY message directly.

C. Voice MAYDAY on Ch 16 must be transmitted first — then the DSC alert follows. The voice call alerts nearby vessels who may not be monitoring DSC.

D. DSC distress is only for MF/HF radio. VHF uses the traditional voice MAYDAY on Ch 16 only — VHF DSC is not a required GMDSS function.

A. NAVTEX — SYSTEM AND OOW USE: NAVTEX (Navigational Telex) is an automated system that broadcasts maritime safety information (MSI) on 518 kHz (international) and 490 kHz (national language) using NBDP (Narrow Band Direct Printing). WHAT IT PROVIDES: (1) NAVIGATIONAL WARNINGS (B messages): hazards to navigation — wrecks, buoy off station, new obstructions, pilot areas, lights changed; (2) METEOROLOGICAL WARNINGS (W messages): gale warnings, storm warnings, weather bulletins; (3) PILOT SERVICE MESSAGES (P messages); (4) ICE REPORTS (I messages); (5) SAR INFORMATION (D messages): distress messages, SAR operations in the area; (6) SUBFACTS and NAVFACTS: submarine exercise areas and other military notifications. HOW IT WORKS: NAVTEX stations broadcast on a schedule. Each station has a unique letter identifier. The NAVTEX receiver is programmed to receive messages from stations covering your sea area. Messages not relevant to the vessel's area can be filtered. OOW DUTIES: (1) Ensure NAVTEX is switched on and printing; (2) Check the NAVTEX receiver is set to receive messages from stations in the current sea area; (3) READ ALL MESSAGES as they print; (4) Bring significant messages (navigational warnings, gale warnings, SAR in the area) to the master's attention; (5) CHART PLOT: plot navigational warnings on the chart/ECDIS; (6) Do NOT ignore NAVTEX messages — they contain safety-critical information.

B. NAVTEX operates on VHF Ch 68 and provides local port information for vessels within 20nm of the coast. It is only relevant when approaching port.

C. NAVTEX is a backup to weather fax and provides only meteorological information. Navigational warnings are only available through the vessel's AIS.

D. NAVTEX messages should be collected and reviewed once per watch. Urgent messages are highlighted in red and require immediate action; all others can wait.