How do you communicate with unauthorized/unidentified aircraft?

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I’ve seen movies in which pilots communicate with unauthorized planes in order to force them to go away/land nearby immediately.. etc.

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Do all planes from all countries have an universal radio frequency? (Even ones flying illegally?) How does it work?

In: 110

In aviation, 121.5MHz is an international reserved emergency frequency called the “Guard” frequency. Generally plane radios can be tuned to their regular channel and guard at the same time, so you always get heard.

Fun fact, in the Incredibles when helen says she’s “Transmitting in the blind guard”, she’s announcing that she’s just speaking on the guard channel to anyone who can hear and help and doesn’t know if she’s actually being received by anyone.

Also, planes are equipped with a device called a ~~squawkbox~~ transponder, which transmits a four-digit code that can be picked up by air traffic controllers. This is normally used to help ATC identify planes in the air but in the event that a plane’s radio is busted, they can set their transponder to squawk a specific number (7700 for general emergency, 7600 for loss of comms, 7500 for a hijacking) to declare what’s gone wrong and allow controllers to plan around it.

Sort of. You can’t “Force” a plane to hear you via the radio, dumbest case they might not have a radio or have it turned off.

But yet, planes to have general “open frequencies” they monitor for the equivalent of “police sirens, pull over” time communications.

In the US, you should monitor 121.5 while in flight. I’m guessing it’s the same elsewhere.

[AIM](https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap5_section_6.html)

>All aircraft operating in US national airspace are highly encouraged to maintain a listening watch on VHF/UHF guard frequencies (121.5 or 243.0 MHz). If subjected to a military intercept, it is incumbent on civilian aviators to understand their responsibilities and to comply with ICAO standard signals relayed from the intercepting aircraft.

This might come as a surprise but US Law does not *require* a privately owned and operated aircraft to have a radio! In fact, there are whole sections of the FAR-AIM dedicated to radioless aircraft operations. Typically this is in case your radios fail mid-flight, but there are still people who will go up in their 1949 Piper Cub that has no radio.

The question is what airspace are you in, when you approach a border of a country then you are required to have an approved flight plan and you have to contact a specific controller to get permission to cross the border. If you fail to do that it could spell a lot of trouble for you. Typically if a plane fails to respond ATC will broadcast on a range of frequencies to find you, they will contact other pilots to see if they have heard the person on the radio, etc. It isn’t all that uncommon for a pilot to accidentally key in the wrong frequency and run silent for a few minutes. It isn’t exactly a panic inducing event.

But yeah, if you approach the American border in 2022 without contacting anyone you are asking for trouble.

Everyone else has described 121.5, but there is another method for use if that fails. There is a single sign that can be given physically by an aircraft. That sign is wiggling the wings. It can have two meanings: “You have been intercepted. Follow me to an airport and land where I land, or you will be shot down.” Or: “I acknowledge your interception and intend to follow you to the airport and land.”

The military also uses challenge and response transponders to identify friendlies and enemies, and is literally called identification friend or foe (IFF). Or at least they used to.

Former ATC here! Planes, including commercial planes, go NORDO (“no radio”) all the damn time, often because the pilot would (a) enter in the wrong frequency in their radio, (b) turn the radio volume all the way down, (c) who the hell knows?

Here’s how we would attempt to contact them, in order of increasing desperation:

1. Try calling them on the frequency they’re supposed to be on.

2. Try calling on “guard” (121.5 MHz).

3. Call the previous air traffic controller over the landline, and ask *them* to try and reach the NORDO plane on their frequency (in the event that the pilot merely forgot to switch to the new frequency).

4. Ask other nearby aircraft to try calling the NORDO aircraft on guard.

5. Let the shift supervisor know, who would contact the airline’s dispatch to try and contact the pilot in another way

6. At some point, things would potentially escalate and a fighter jet might get scrambled. I’ve never witnessed that though.