What are 121.5 VHF and 243.0 referred to in aviation?

The frequencies 121.5 VHF and 243.0 are referred to as universal emergency frequencies in aviation. These frequencies are specifically designated for emergency communication and are recognized internationally for distress and safety situations.

The VHF frequency 121.5 is primarily used by civilian aircraft, while 243.0 MHz is the corresponding frequency for military aircraft. Both frequencies serve as a standard means for all aircraft to communicate critical information in an emergency, ensuring that help can be summoned regardless of the type of aircraft or geographical location. This universality is crucial during emergencies where prompt communication can save lives.

Other frequency types, like standard communication frequencies or navigation frequencies, do not pertain to emergency use and do not share the same level of international recognition for distress situations.