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In the USA airport facilities directory (AFD), some towers (eg KSJC) are listed with the note:

Emerg frequency 121.5 not avbl at tower.

Why do these facilities not monitor guard? Does the note actually mean that they cannot even talk on 121.5 in an emergency?

I am assuming it is because a different facility in the area (eg a TRACON) is monitoring guard, and they don’t want two facilities taking responsibility for guard. But suppose an airplane is landing in an emergency, does that mean the tower couldn’t even listen to the emergency communications?

How does this work practically in emergencies?

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    $\begingroup$ It's hard to imagine being close enough to KSJC that you need to talk to them, yet not being in contact with some ATC facility on a frequency other than 121.5. $\endgroup$
    – Riccati
    Dec 18 '15 at 23:17
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    $\begingroup$ 121.5 is only used when you don't have anyone specific to speak to or those who do can't help you - for example, having access to primary RADAR. If they direct you to land at an airport, you'll be handed over to the tower as any other approach - probably coordinated via phone between the controllers. $\endgroup$
    – Dan
    Dec 18 '15 at 23:40
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It seems to come down to the point that as long as someone is monitoring 121.5 in a specific airspace then not everyone needs to. And it helps avoid multiple ATC facilities responding to the same call. This is from the FAA's Facility Operation and Administration orders (my emphasis):

3-3-4. EMERGENCY FREQUENCIES 121.5 AND 243.0 MHz

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d. When facilities are in proximity and no derogation of services will result, transmit/receive capability should not be provided for each facility. The following requirements shall be maintained:

  1. Geographical area coverage shall not be derogated.

  2. DF-equipped facilities shall have transmit/receive capability on 121.5 MHz.

  3. Facilities without emergency frequency capability shall have appropriate landlines for rapid relay of emergency information.

Looking at KSJC, there are a lot of other airports close by, so the potential for confusion or conflict on the frequency seems high. My guess is that they leave 121.5 to NorCal TRACON; KPAO is 10 miles from KSJC and also doesn't have 121.5 available, for example.

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    $\begingroup$ I have flown around SJC in a helicopter at 500ft with good radio and radar coverage from Norcal Approach. The antennas are up on on the surrounding mountains. $\endgroup$
    – rbp
    Dec 24 '15 at 18:42

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