1. Commit 121.5 to memory. The UHF emergency frequency is 243.0 -- that's easy to remember because it's exactly double 121.5. If you have a radio, it must be able to communicate on 121.5. (CARs 602.143)

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2. 121.9 is not any special frequency, but it's quite a common ground control frequency, especially in the United States.

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3. 122.2 is the United States "Flight Watch" frequency, for PIREPs and weather.

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4. 126.7 is the Canadian enroute frequency.