EPIRBs and SART/AIS-SART
EPIRB
An Emergency Position-Indicating Radio Beacon transmits a distress alert via satellite (COSPAR-SARSAT) and provides a homing signal for rescue units. Modern EPIRBs are activated manually or automatically by water immersion when the vessel sinks, and float free from their bracket. They transmit an identity (usually linked to the vessel's MMSI) and, where fitted, a GNSS position. Traps include thinking an EPIRB provides voice communication (it does not), confusing the 406 MHz alert with the 121.5 MHz homing signal, and forgetting that an EPIRB must be registered with the national authority so that the identity can be linked to the vessel.
SART and AIS-SART
A Search and Rescue Transponder is a radar transponder that, when interrogated by a radar, produces a distinctive series of dots on the radar display, helping locate a survival craft. An AIS-SART achieves a similar purpose by transmitting AIS messages that appear on AIS displays. Neither provides voice communication. A trap is expecting a SART to appear on every radar; it responds to radars in the appropriate band and within range, and the pattern must be recognised.
Testing and maintenance
EPIRBs and SARTs should be tested according to manufacturer instructions, typically using a self-test function that does not transmit a live alert. Batteries and hydrostatic releases have expiry dates and must be replaced. False alerts from EPIRBs must be reported and cancelled promptly.
Worked example
A vessel sinks; the float-free EPIRB activates automatically and transmits a 406 MHz alert with position, while the crew takes the SART to the liferaft. Rescue aircraft home on the EPIRB's 121.5 MHz signal, and rescue vessels detect the SART on radar. The EPIRB alerted; the SART located.