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On my radio, an ICOM A210, I can't tune 121.62 (the clearance delivery frequency at KMSN). How can I tune a frequency ending in 2?

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    $\begingroup$ ... and your question is? $\endgroup$ – ratchet freak Nov 6 '14 at 15:23
  • $\begingroup$ This page shows the frequency range as 118.000–136.9xxMHz. $\endgroup$ – Farhan Nov 6 '14 at 15:27
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    $\begingroup$ Can you explain exactly how you're trying to tune the frequency and why you can't select 121.62? What exactly happens? $\endgroup$ – Pondlife Nov 6 '14 at 15:29
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    $\begingroup$ Can you contact them on 121.625? The frequency you list (though it's that way in the A/FD also) may be a typo, since airband in the US still uses 25kHz spacing. $\endgroup$ – NathanG Nov 6 '14 at 16:19
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    $\begingroup$ @NathanG Most 25kHz radios drop the last digit, so when you put in 121.62, it is actually tuning and using 121.625. Others show the last digit, so tuning 121.62 would be impossible, although as you say, 121.625 is most likely what he wants. $\endgroup$ – Lnafziger Nov 6 '14 at 16:53
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As a complete guess, you're trying to tune 121.620, but you should just be tuning 121.625. From AOPA (emphasis mine):

All aviation communication, VOR, and ILS frequencies are in the 100 MHz band, so the first number is always "1." The hundredths digit can be only 0, 2, 5, or 7; 1xx.x2 implies 1xx.x25; and 1xx.x7 implies 1xx.x75--when a frequency is assigned, the ending "5" is often omitted. Trailing zeros in the hundreds and thousandths positions are always omitted in voice transmissions.

The standard frequency spacing in the US is 25kHz.

Omitting the last digit is also described in the FAA's ATC instructions:

  1. The separate digits of the frequency, inserting the word “point” where the decimal point occurs.

(a) Omit digits after the second digit to the right of the decimal point.

They include this example:

135.275 MHz “One three five point two seven.”

And although this probably isn't your issue, it's worth noting that some radios tune in 50kHz increments by default, unless you pull out (usually) the tuning knob to enable 25kHz tuning. I've been momentarily confused by that several times in unfamiliar aircraft. I assume this isn't the issue you have, though, since the manual for the A210 says it uses 25kHz spacing.

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I called KMSN tower, they said 121.625 should work as well or, just call ground which is what I did last time I was there.

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    $\begingroup$ 121.625 should not work "as well", it is the frequency that should work. $\endgroup$ – Jan Hudec Nov 6 '14 at 19:53
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Just to put a point on the answers already here, there is no actual assigned aviation frequency 121.62. You add a 5 if the 5th digit is a 2 or a 7. Some radios display the 6th digit, some don't.

It's further confusing where 8.33 kHz channels (in Europe, and in some special cases like flight test frequencies or company frequencies) are used. Between 121.600 and 121.625 are two other frequencies, which are actually 121.60833... and 121.61666... MHz, referred to by their "channel names" as 121.610 and 121.615. Eurocontrol mandates saying all six digits for the split channels.

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