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I was thinking, what would happen if the radio systems for an ATC tower fail due to power loss or faulty systems?

Is there any kind of backup radio that would be used to contact the planes and/or any procedures that the planes and ATC would follow?

Edit: And if there is a backup radio, what happens if that fails too?

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    $\begingroup$ I think the last time a total ATC failure happened at an airport was 2011, Sendai Airport during the Tsunami. By the time the radio and radar went out it was patently obvious that having your plane on the ground there was not anyone's idea of a good time. Other ATC was managing diversions. Like the answers below state, it's really only a total-catastrophe situation that can completely knock out radar and radio. Short of major physical destruction the backups can deal with almost anything. And if the site has suffered such massive damage then there are bigger problems to worry about. $\endgroup$ – J... Sep 1 '17 at 12:03
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    $\begingroup$ I was doing an IFR training flight and when we asked for a clearance we were told "Columbus is dark." We were flying out of KOSU and talking to controllers there but KCMH was unreachable and apparently all traffic was being worked by Center. I never found out what actually happened but ended up bagging the lesson as the KOSU controllers told us there were only the 2 center controllers working everything. This was within the past two months. $\endgroup$ – N Klosterman Sep 1 '17 at 13:49
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    $\begingroup$ There was an incident in 2014 where an employee of a contractor working at Chicago Center deliberately sabotaged the equipment as part of a suicide attempt, disabling the entire facility. This wasn't exactly a normal case, though, and it's not clear that any number of backups would have kept the Center running. $\endgroup$ – Michael Seifert Sep 1 '17 at 15:48
  • $\begingroup$ There was also an incident at Miami TRACON about a year ago. $\endgroup$ – reirab Sep 1 '17 at 21:20
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There is always a backup radio system as well as a several backup systems like for example a backup CWP (controller worker position) in case the primary fails. PANS-ATM (ICAO doc 4444) in chapter 2.5 SAFETY REVIEWS mentions that

Operational and technical issues to ensure that: [...] communications, navigation, surveillance and other safety significant systems and equipment [...] include adequate backup facilities and/or procedures in the event of a system failure or degradation.

Emphasis is mine.

Also there is a standby generator (or even more than one) that has to instantly take over in case of power supply failure but I can't find any regulations at the moment.

As for the "what happens if the backup fails as well" question, we need to see the fuller picture that the document provides:

d) communications, navigation, surveillance and other safety significant systems and equipment:

1) are tested for normal operations on a routine basis;

2) meet the required level of reliability and availability as defined by the appropriate authority;

3) provide for the timely and appropriate detection and warning of system failures and degradations;

4) include documentation on the consequences of system, subsystem and equipment failures and degradations;

5) include measures to control the probability of failures and degradations; and

6) include adequate backup facilities and/or procedures in the event of a system failure or degradation;

Emphasis is again mine

As you can see backup is the last line of defense. An ATS unit should ensure that equipment is regularly maintained, it's monitored, it's tested and any failures should be prevented if possible and their impact being documented.

If everything else fails, then you use the backup. And again the "include adequate backup" phrase can be translated as "if one thinks that a second backup is needed they should install one". But the previous 5 clauses are there to eliminate that case.

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If the power fails, the tower will automatically switch to backup power generated by local diesel generators. If that fails, there are backup handheld radios. If those fail, the tower has a battery powered light gun for transmitting visual signals. So the risk of losing all forms of communication is next to none.

Everything is backed up in ATC. Radios, radar screens, flight strip printers, phone lines and so on. And should the unthinkable happen and the coffee machine fails, there is usually a backup of that as well.

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    $\begingroup$ The light gun works for Tower, but not so much for TRACON or Center. The backup handhelds are also not really sufficient in those cases. But, of course, the worst case is ATC services being unavailable for an entire country, such as in an ATC strike. $\endgroup$ – reirab Sep 1 '17 at 21:17
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    $\begingroup$ I assume that the ATC strike is the result of both the primary and backup coffee machines becoming inoperative. $\endgroup$ – reirab Sep 1 '17 at 21:17
  • $\begingroup$ @reirab One should think so! Just a note though, when air traffic controllers strike, ATC facilities do not close down. Unions have agreements with the service providers to always provide a minimum service, such that emergency flights, state flights, military flights and usually even overflights will be handled. $\endgroup$ – J. Hougaard Sep 2 '17 at 6:13

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