Emergency position-indicating radio beacons (EPIRB) and search and rescue radar transponders (SART)
406 MHz EPIRB
A 406 MHz EPIRB transmits a digital distress alert to the Cospas-Sarsat system, with a low-power 121.5 MHz homing signal for aircraft and SAR units. GNSS-equipped beacons include position in the alert. The beacon must be registered with the national authority, with vessel identity, contacts, and survival-craft details. Float-free mounting uses a hydrostatic release unit (HRU) that releases the beacon at depth and allows it to float and activate. Battery and HRU expiry dates are surveyed. Test mode checks the transmitter and battery without transmitting a live distress alert.
SART and AIS-SART
A radar SART operates in the 9 GHz band, responds to an interrogating radar, and produces a series of dots on the radar display. It is a locating device, not a satellite alerting device. Battery capacity is typically 96 hours standby and 8 hours transmission. An AIS-SART transmits AIS position reports and appears on AIS, not as radar dots. Both should be mounted where they can be deployed into a survival craft and tested according to the manufacturer's instructions.
Worked example
A SART does not appear on the radar during a drill. The radar is on the 3 cm band and tuned, but the SART is lying flat inside the wheelhouse. Correct: mount or hold the SART upright at least about 1 m above the water or deck, switch it on, and observe at about 2 nautical miles. If no response, check the battery and test function. The reasoning: SART response depends on polarization, height, and interrogation by an X-band radar; a flat, shielded position gives no usable return.
Traps
Do not test a 406 EPIRB by pressing the live distress button. Do not ignore an expired HRU or battery. Do not paint over the EPIRB strobe or antenna. Do not treat a SART as a satellite beacon. Do not confuse AIS-SART with radar-SART displays. Do not store the SART where it cannot be reached after abandonment.
Key facts
406 MHz alerts Cospas-Sarsat; 121.5 MHz is homing. EPIRB registration must be current. SART is X-band radar locating. AIS-SART appears on AIS.