Definition
Specific radio frequencies reserved for distress and urgency communications, monitored continuously by air traffic control facilities and search and rescue services. The two primary aviation emergency frequencies are 121.5 MHz (VHF, civilian) and 243.0 MHz (UHF, military), often called the VHF and UHF guard frequencies.
Plain English
Special radio channels set aside for pilots in trouble. Controllers and rescue services always listen on these channels, so a call for help will be heard.
Context Anchor
Seen in emergency, lost-communication, and instrument procedure discussions where a pilot may need to contact help quickly.
Derivation
Emergency comes from a word meaning to arise or come out suddenly. Frequency, in radio use, means the exact rate a radio signal uses, which pilots experience as a specific radio channel such as 121.5 MHz.
Why Pilots Care
Tuning to these frequencies gives the best chance that a distress call will be heard immediately by someone who can help.
Grounding Statement
If the normal radio path is not working and the situation needs immediate attention, emergency frequencies are the backup place to call for help.
Intuition Check
Do not read this as any frequency used during an emergency. In aviation, emergency frequencies are specific recognized radio frequencies reserved or monitored for urgent help.
Example Sentence 1
After losing communication with Center, the pilot tuned 121.5 and called on the emergency frequency.
Example Sentence 2
During preflight planning the instructor reminded the student to keep the emergency frequencies in the standby position.