Which piece of equipment broadcasts an alert frequency of 121.5 and 243.0?

The correct answer is the emergency locator transmitter (ELT). ELTs are designed specifically to broadcast distress signals on the emergency frequencies of 121.5 MHz and 243.0 MHz. These frequencies are recognized internationally for search and rescue operations, allowing aircraft in distress to communicate their location to rescue services.

When an aircraft experiences an emergency, the ELT activates automatically or can be triggered manually, sending out a continuous signal that helps rescuers find the aircraft quickly. The 121.5 MHz frequency was the traditional frequency for ELTs, while 243.0 MHz serves as a military emergency frequency.

While other equipment such as transponders, VHF radios, and GPS locators serve vital communication and navigation functions, they do not specifically function to transmit distress signals on these designated emergency frequencies as an ELT does. This specialized purpose is what makes the ELT crucial for safety in aviation emergencies.