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I was reading this question about how do pilots send distress signals in emergency scenarios, and that got me thinking...

In voretaq7's answer, he states that there are three ways to send distress signals, one of them is by the aircraft's transponder

Three transponder codes are reserved for unusual/emergency situations:
- 7700 for general emergencies.
- 7600 for loss of communication (radio failure).
- 7500 for hijacking or other unlawful interference.

I can understand the reason to squawk both 7500 and 7600 in the appropriate situation, but I'm failing to understand why squawk 7700 in an emergency scenario.

So that's what I'm thinking:

  • In case of a hijack, the ability to squawk 7500 to silent alert the ATC of the situation, without the hijacker knowing, is an advantage.

  • In case of a radio failure, where you can't alert the ATC over the radio, the ability to squawk 7600 and make them aware of your situation, is an advantage.

  • In case of emergency, where the pilots are trying to handle a lot of things (high workload scenario), to stop everything to configure the aircraft's transponder, when they are communicating with the ATC by radio, doesn't seem like a good thing to do.

So, finally, here are my questions:

  • Is it common for pilots to squawk 7700 in emergency scenarios?
  • What are the advantages, for the pilots, to squawk 7700 in emergencies situations?
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    $\begingroup$ changing to 7700 is probably just a single button press. $\endgroup$ – ratchet freak Jun 11 '15 at 13:05
  • $\begingroup$ There's already a partial answer to this: aviation.stackexchange.com/questions/2163/… $\endgroup$ – Andy Jun 11 '15 at 13:29
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    $\begingroup$ There are a few examples in aviation where an aircraft has been in trouble, but due to language barriers has failed to correctly make the seriousness of this situation known to air traffic control. Look up Avianca Flight 52 as an example. They were low on fuel, and eventually crashed due to fuel starvation, with ATC not being aware how bad their situation was. Squawking 7700 would have saved lives in this case. $\endgroup$ – Gavin Coates Jun 11 '15 at 15:54
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    $\begingroup$ Avianca Flight 52 $\endgroup$ – RJFalconer Jun 12 '15 at 9:54
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    $\begingroup$ Even if you are in communication with ATC and they request you to squawk 7700, which they most likely will, you fly the aircraft first. If I was really busy, I would probably just respond 'Standby'. If I was super busy and I am about to die if I don't get this right, I wouldn't even respond. Only when I have sorted myself out, will I then think about changing the squawk. To be frank, I wouldn't even bother replying back to ATC following the standby since they will know quicker than I can call them. Aviate, navigate, communicate. People have died because the pilot didn't do those things. $\endgroup$ – Simon Aug 21 '15 at 10:31
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If you make a radio call, unless you are on 121.5 (or 243 military), then only the station you are talking to will initially know about the emergency. Initial calls should always be with the unit you are working with unless you are VFR.

If you squawk 7700, then all stations in transponder range, including possible airborne stations such as AWACS and SAR will know right away that you are in trouble, with position, altitude and possibly aircraft type and flight number.

If VFR, you might not be talking to anyone and may not have the frequencies of nearby units easily to hand.

Squawking 7700 is definitely a good thing.

You mentioned being busy. The mantra drilled into everyone is "aviate, navigate, communicate". In most circumstances, fly the plane, fly it where you want it to go, then tell someone about it. Squawking 7700 will be one of the last actions carried out.

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    $\begingroup$ Nice informed answer. I think that is exactly what these transponders are designed to do; to provide that 'extra' link. A code, with no possibility of verbal garbling. A Wide Area distress, with no need to try to initiate comms, possibly in eighteen different languages to dozens of busy people, who mostly don't expect, and won't be able to quickly understand why you are calling them out of the blue, haha. No seriously. $\endgroup$ – Andyz Smith Jun 11 '15 at 19:18
  • $\begingroup$ Thanks for your answer. If I squawk 7700, will it change how other nearby planes' instruments display me(radar, tcas, etc)? $\endgroup$ – Gabriel Brito Jun 12 '15 at 11:44
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    $\begingroup$ @GabrielBrito On "normal" aircraft, no. They have no equipment to interrogate other transponders apart from TCAS and AFAIK, regualr TCAS does not have any special symbology for displaying an aircraft squawking an urgency code. AWACS, SAR etc will but I don't know details. $\endgroup$ – Simon Jun 12 '15 at 12:17
  • $\begingroup$ @Simon: What about ADS-B In/TIS–B displays? Unlike TCAS which is rigid and limited in its display, I am under the impression that there is basically no standardization of ADS-B/TIS-B displays. Therefore it is reasonably likely that some will choose to flag emergency aircraft to help VFR craft remain well clear. Sure, very few aircraft have them at the moment, but I suspect adoption will be reasonably rapid in glass cockpits since only a UAT or 1090ES transponder and a firmware upgrade are likely to be needed. $\endgroup$ – Kevin Cathcart Jun 12 '15 at 20:28
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    $\begingroup$ Interconnection of ATC systems is making your first point moot; ATCs especially at larger airports can flag an aircraft as under an emergency, and every other screen within radar range would know in seconds. $\endgroup$ – KeithS Sep 21 '15 at 16:23
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Aircraft squawking 7700 are getting a special indication (e.g highlighted, distinct colour, boxed) on Air Traffic Control (ATC) displays. This helps to identify the emergency aircraft not only to the air traffic controller who is controlling the airspace the aircraft is in, but also to controllers of other (nearby) airspaces. This helps to improve awareness and coordination within ATC.

In case of emergency, where the pilots are trying to handle a lot of things (high workload scenario), to stop everything to configure the aircraft's transponder, when they are communicating with the ATC by radio, doesn't seem like a good thing to do.

Typically communication to ATC, including setting the transponder to the general emergency code is of low priority during an emergency:

  1. Aviate (make sure the aircraft keeps flying),
  2. Navigate (make sure you know where you are going, don't fly into terrain while trouble shooting),
  3. Communicate (let others know what you are doing)

Usually communication to ATC will be done using radio communications, but in some cases that may be difficult and setting 7700 will get the message that something is wrong across.

Often ATC will ask to squawk 7700 after the initial Mayday call to identify the aircraft not only to the controller you are talking to, but to other controllers responsible for nearby sectors as well. This aids in coordination between controllers and makes sure appropriate action can be taken by controllers of adjacent airspace / airports in preparation of the emergency aircraft's transition into their area of responsibility.

This video with ATC recordings of an emergency situation at Manchester airport shows you an example of ATC requesting an aircraft to squawk 7700 (at 2:00).

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  • $\begingroup$ Thanks for your answer! Is it procedure to squawk 7700 after the initial Mayday call? $\endgroup$ – Gabriel Brito Jun 12 '15 at 12:01
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    $\begingroup$ @GabrielBrito It think it is, it may vary from operator to operator, but I need to verify that. I am quite busy at the moment so I'll confirm next week. $\endgroup$ – DeltaLima Jun 12 '15 at 12:05
  • $\begingroup$ @DeltaLima Did you ever look that up? $\endgroup$ – a CVn Dec 4 '16 at 19:50
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Because it gets highlighted immediately on ATC's equipment, without needing a lengthy radio message to describe the problem and identify one's position.

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    $\begingroup$ Without the radio message how can the ATC be aware of the nature of the emergency? $\endgroup$ – Gabriel Brito Jun 11 '15 at 13:15
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    $\begingroup$ they can't. but ATC can see there's a problem and direct all the other planes out of the way $\endgroup$ – rbp Jun 11 '15 at 13:23
  • $\begingroup$ Good question about the radio message. The first aim must be to make ATC aware of location, in case an actual forced landing occurs. I should have said that a radio call should be placed too, but as it's away from the airfield the pilots would be forced to resolve the situation themselves, at least initially. $\endgroup$ – Andy Jun 11 '15 at 13:26
  • $\begingroup$ I've found a linked answer by the way - added as a comment to the question itself. $\endgroup$ – Andy Jun 11 '15 at 13:30
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Concur with the other commenters that there are advantages to squawking 7700 at the appropriate time in the aviate, communicate, navigate steps. There is one situation not mentioned so far in which it might be especially important: when an emergency occurs after loss of communications for an IFR flight in IMC.

If an IFR flight loses communications while in VMC, the pilot is supposed to continue the flight under VFR and land as soon as practical (FAR 91.185). So if there is good weather out, and you set your transponder to 7600 and deviate from your IFR clearance by turning towards an airport at which you're going to land, ATC has a pretty good idea of what you're going to do and can act appropriately.

But what if you're in IMC? If you set your transponder to 7600 and proceed in accordance with the IFR lost-comm procedures, ATC will assume that you're going to continue to proceed in accordance with them (route assigned, vectored, expected, or filed; altitude highest of the minimum IFR altitude, expected altitude, or assigned altitude). But what if a different emergency occurs at that point and you need to deviate from that plan? If you then squawk 7700, ATC will know that you are deviating not because you're in VMC and continuing under VFR, but because you have an emergency and are exercising your PIC authority.

What good is that when ATC can't talk to you? I'd much rather ATC send emergency assistance to whatever airport I'm headed for or wherever I disappeared from their radar scope rather than waiting for me to call them on the ground. And it certainly helps that they're going to clear the skies of all traffic anywhere near me. Obviously if you have your hands full flying the plane then setting the transponder isn't a priority, but it does offer you considerable advantages if you have the time to do so.

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  • $\begingroup$ +1, the nuances of IFR do require special consideration, which this answer provides. $\endgroup$ – Cosmic Ossifrage Oct 19 '15 at 16:16
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As many others have mentioned here, if you squawk 7700 you will be highlighted on the ATC screens. ATC will in turn clear traffic around you. The advantages to this are obvious if you consider that you may be suffering controllability problems that are preventing you from being able to maintain heading or altitude.

Couple this with the fact you may also be having trouble communicating with ATC. This may have nothing to do with radio trouble, as anyone can attest who has flown in a high density area (O'Hare, JFK, Atlanta, etc...) where the radio comms can be so clobbered that you can continually get stepped on. Aviate, navigate, communicate and 7700 is communicating.

I have had in-flight emergencies that I didn't put 7700 in because I already had a discreet squawk and ATC answered immediately when I declared the emergency with my intentions to turn and descend. Had they not responded, I would have put 7700 in and done what I needed to do to handle the emergency knowing that ATC would vector other traffic around me.

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Transponder code 7700 immediately gets the attention of the controllers. They will know your location, direction of flight and altitude. This is extremely important in that they will convey this information to emergency services personnel who will be able to locate your (possible) crash site much faster. That is the primary reason to use this code. As a SAR mission pilot I can tell you it takes a very long time to call out an aircrew, launch and locate a downed aircraft. Aviate is always number one. If you do not maintain control of the aircraft is doesn't matter how long it takes to find it, you're still dead. If you are already on a discreet code and talking to a controller they will know where you are already and declaring an emergency will get you their full attention. Believe me you want the attention. If you are VFR at 3000 AGL and run out of fuel (happens a lot, really) squawking 7700 is faster than looking up a frequency and the conversation will not be of immediate help anyway. They will know someone is in trouble at x location, with x heading, with x descent rate and radar contact lost at x altitude. Help will be on the way.

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Having worked as both a controller and flight instructor, there is a lot of misinformation and outright guesses in here.

If you are already speaking with ATC and are on an assigned squawk code, do not change to 7700 unless you are explicitly instructed to. You have already been radar identified, they already know where you are. Most of the comments regarding your presentation on the radar display are wrong (e.g. it does not "light it up like a Christmas tree"). While it varies depending on the equipment and software, generally it will just add a small tag to the bottom of the data block that says something like EMER. That's not really necessary if you've already been radar identified, and as the OP said, pilots in an emergency situation have higher priorities than adjusting their transponders unnecessarily.

Now. If you are NOT already speaking with ATC, yes, this is a good idea. For the systems I am familiar with, a plane which was previously squawking 1200 that has changed to an emergency code (i.e. 7700) will force a larger datablock to appear on the display. This can aid identification (though it does not positively radar identify you for other reasons). Think of it as the transponder version of making a mayday call.

Another erroneous answer suggests that it can help other ATC facilities locate you. Sort of, but not in a particularly useful way. If anything, it adds work because those facilities are now calling the airspace that aircraft is in to verify it is being addressed; any shared identification will be handled appropriately by the controller and isn't something you need to worry about in an emergency situation.

I do agree with the person who suggested it'd be a good idea if one was already NORDO and needed to deviate from their clearance due to an emergency.

The overall principle to understand is that squawking 7700 is to aid ATC in identifying you. If you're already talking to them because of flight following or IFR flight, you're already identified - it's unnecessary. If you haven't been speaking with them, go for it.

Having worked several emergencies in my career, I did not have any instances where 7700 was used. There are the rare occasions when a controller may request it from a plane which is already on a discrete transponder code, but they are uncommon and related to ATC issues that a pilot wouldn't be aware of (for example, ease of identification in an area where conflicting control systems make point outs a hassle).

In any case, if you're already on an assigned squawk, keep it unless told otherwise. If you're on 1200 and don't already have ATC's attention, 7700 is one way to do so.

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A former tanker instructor, who I had at Flight Safety, emphasized that when a single pilot work load is high, and one is working an emergency, squawking 7700 gets to controller's attention, allows him to start planning, while the pilot can be focused on debugging the situation. From a time and effort cost standpoint setting the transponder to 7700 takes less time than a radio call, and one can then ignore the multiple radio calls that may come in, until one has the bandwidth to handle the communications.

Years later, I had a panel fire at cruise, on a night IFR trip. Conditions were largely VMC. While working the fire, I squawked 7700. The transponder got a couple of replies in, until I determined that I would kill the aircraft master. Minutes later the smoke had cleared, and I found my trusty brick aviation radio and called ATC. They knew something had happened, as they saw 7700, and then they lost my secondary radar return.

They knew something was happening, and cleared traffic in my vicinity and particularly below me. When I came back on, using a handheld, I was ready to tell them all the stuff they needed to hear (nature of the situation, fuel and souls) and I continued to my (nearby) destination. Aside from pumping down the gear and having no lights, the flight was uneventful from that point on.

I could not have had even a short interchange with ATC in the time it had taken to squawk 7700, and moments later shutdown the aircraft master.

To answer the OP questions:

-Is it common to use 7700? Probably, but what is your definition of "common"?

-Advantages?
1. No need to talk, especially if at a time when talk is distracting or not possible.
2. If not talking with ATC, ATC (and TCAS) has immediate awareness that your aircraft has an issue, and knowledge of where you are. 3. Saves words, telling ATC you have an emergency.

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When you squawk 7700 you have to use your brains and hands to do other things besides flying the plane and troubleshooting your emergency. You also light up the controllers scope like a Christmas tree, which is very distracting, causing them to quickly assign you a discreet code, meaning that you will be tempted to move your hands, yet again, to something that doesn't matter.

Much easier than squawking is to simply declare an emergency on the radio frequency you are already monitoring. If I need to literally move my hands to squawk emergency then I've probably given up on the FAR/AIMS anyway because I'm about to die. IE, electrical failures effecting both radios probably caused by a dual engine fire affecting both generators.

"77, going to heaven"--your mileage may vary.

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  • $\begingroup$ Thanks for your answer. What is FAR/AIMS? And why would you give it up? $\endgroup$ – Gabriel Brito Jun 12 '15 at 11:52
  • $\begingroup$ @GabrielBrito Federal Aviation Regulations and Aeronautical Information Manual. $\endgroup$ – NobodyNada Jun 13 '15 at 19:51
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    $\begingroup$ Spoken like a true single seater. Setting this transponder code is what the co-pilot (or back-seater) is for (if you have one). $\endgroup$ – Scooter Jun 13 '15 at 23:22

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