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Coast patrol has a dedicated frequency for emergency that must be watched at almost all hours, and even if I recall, it had a "dead silent period" to prioritise whatever emergency might be reported. Is there a dedicated frequency for aviation? Or shall MAYDAYs just be sent to the standard ATC frequency?

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Remember to squawk 7700 if appropriate. If no frequency will work for you, then 7600 (ICAO standard for loss of comms). –  Mac Plewa Jan 13 at 6:25
    
Assuming you are talking about verbal communications this is the best answer below. However, as far as emergency frequencies in general there are others such as 406.0-406.1mhz that is used for Emergency Locator Transmitters. They give a specific identification code assigned by NOAA that can be picked up by satellite to aid in both crash identification as well as search and rescue effort. –  p1l0t Jan 13 at 18:45
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4 Answers 4

up vote 17 down vote accepted

If a pilot is already speaking to ATC (or monitoring a frequency) they should continue to use that frequency for any emergency or abnormal situation.

If they are not currently receiving ATC services or on an ATC frequency, attempt to use 121.5. Many ATC providers and enroute airliners monitor this frequency and can relay or provide assistance.

The FAA's AIM (6-3-1) describes emergency use of 121.5 in the United States:

h. Although the frequency in use or other frequencies assigned by ATC are preferable, the following emergency frequencies can be used for distress or urgency communications, if necessary or desirable:

1. 121.5 MHz and 243.0 MHz. Both have a range generally limited to line of sight. 121.5 MHz is guarded by direction finding stations and some military and civil aircraft. 243.0 MHz is guarded by military aircraft. Both 121.5 MHz and 243.0 MHz are guarded by military towers, most civil towers, FSSs, and radar facilities. Normally ARTCC emergency frequency capability does not extend to radar coverage limits. [emphasis mine] If an ARTCC does not respond when called on 121.5 MHz or 243.0 MHz, call the nearest tower or FSS.

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Yes, the aircraft emergency frequency (which we often call "guard") is 121.5 MHz.

This is monitored by many control towers and flight service stations. It is also typically monitored by airplanes on cross-country trips (especially airliners). You will occasionally hear ATC ask an airplane to try to contact another airplane "on guard" in an attempt to relay a message to an aircraft which they have lost communications with.

However, if you are currently in communication with ATC on another frequency, or there is a frequency where you know you can communicate your distress and it will be heard, you should use that frequency instead, because there is no guarantee your message will be heard on 121.5 in all parts of the country/world.

Older ELT's (emergency locator transmitter) also transmitted a siren type sound on this frequency when activated which sounds like this.

In addition, it is used as an intercept frequency. In other words, if you get intercepted by a fighter jet, you better be listening in on 121.5 for any commands they give you.

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ATC would most probably ask other aircraft to relay messages to a not responding aircraft on the current frequency, as both aircraft are supposed to be monitoring this. Guard is only rarely used for this purpose and not mend to. These messages commonly includes the instruction for the 'lost' (not talkin about navigation) to check in on another frequency as they are outside the line of sight (VHF communication) or range of the receiver transmitter for this ATC frequency. –  Falk Jan 10 at 3:02
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@Falk that's true, and the more common situation. I said occasionally because I have heard it happen occasionally. –  Bret Copeland Jan 10 at 3:23
    
No worries, I just like to add this because guard is already 'abused' far too often and I like to avoid this as far as possible. Everything I receive on guard is getting all my capacity I don't need to actually fly the aircraft. If the transmitting station may be some further away, parts of a simple chat could sound like an emergency call and I'm probably not the only one who's then carefully monitoring .5 and maybe forgetting about something he was about to do (some nearly worst case - actually worst case would be hearing an emergency call and thinking it's one of these abuses of guard) –  Falk Jan 10 at 3:40
    
Why is it called guard? I know the frequency is 'guarded' - but what does that even mean? –  Harv Jan 10 at 22:52
    
@Harv that's a separate question. If you'd like to ask it on the site, please feel free. –  Bret Copeland Jan 11 at 1:37
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As a general rule, declaring an emergency should be done on the frequency you are currently communicating on. However, there is a dedicated emergency frequency as Bret said (121.5 MHz), which is the same all over the world. It's generally used if there is no response from the ATC facility the pilot was communicating with.

On many glass cockpits there's even a shortcut to tune to the emergency frequency. For example, on Garmin equipment like the G1000 and G530/430 you have to press and hold the "flip-flop" key for 2 seconds and it will automatically tune 121.5 for you.

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Canada has similar procedures to the US. From the Transport Canada Aeronautical Information Manual, in the COM section:

5.11 Emergency Communications

[...]

The first transmission of the distress call and message by an aircraft should be on the air-to-ground frequency in use at the time. If the aircraft is unable to establish communication on the frequency in use, the distress call and message should be repeated on the HF general calling or distress frequency 3 023.5 kHz, 5 680 kHz, 121.5 MHz, 406.1 MHz, or other distress frequency available, such as 2 182 kHz, in an effort to establish communications with any ground station or the maritime service.

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