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I know that modern jetliners often have a multitude of radio equipment on board, including VHF, HF, satellite, etc.

From what I've read (such as here), it's customary for jetliners to monitor 121.5 MHz for aircraft emergency traffic.

Do commercial airliners traveling transoceanic routes also monitor marine VHF channel 16 (156.8 MHz), a common frequency used by ships in distress?

If so, is this a fairly customary, routine matter (like monitoring 121.5 MHz) or is it simply up to the crew of each aircraft?

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    $\begingroup$ "From what I've read, it's customary ". Just wondering where you read that if you remember. $\endgroup$ – user6035379 Feb 19 '17 at 11:45
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    $\begingroup$ @user6035379 Good question. I don't recall, exactly. I have a tendency to browse Wikipedia and Stack Exchange with many tabs, but it was most likely on one of those two sites. $\endgroup$ – heypete Mar 4 '17 at 23:02
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156.8 MHz

Crews don't listen to channel 16 of the marine band.

Channel 16 is used by marine with FM, while a VHF aviation receiver demodulates only AM, and the upper limit of the VHF band for aviation is 137 MHz.

Channel 16 is monitored by local marine agencies -- coast guards -- e.g. CROSS in France and USCG in the US.

Aircraft are only required to carry an equipment able to receive and transmit on emergency frequencies used by aviation.

Emergency frequencies other than channel 16 are also used in marine, including 121.5 MHz, e.g. by EPIRBs. The use of 121.5 MHz for marine EPIRBs was to allow monitoring by aircraft.

Air regulation for listening 121.5 MHz

EPIRBs monitoring by aircraft is not relevant any more as EPIRBs are now efficiently monitored by satellite (COSPAS-SARSAT). However 121.5 MHz is still monitored ("guarded") by aircraft, in particular for interception response purposes. The requirement is specified in ICAO Annex 10 (volume II) to the Chicago Convention:

5.2.2.1.1.1 Aircraft on long over-water flights, or on flights over designated areas over which the carriage of an emergency locator transmitter (ELT) is required, shall

  • continuously guard the VHF emergency frequency 121.5 MHz , except for those periods when aircraft are carrying out communications on other VHF channels or when airborne equipment limitations or cockpit duties do not permit simultaneous guarding of two channels.

5.2.2.1.1.2 Aircraft shall continuously guard the VHF emergency frequency 121.5 MHz in areas or over routes where the possibility of interception of aircraft or other hazardous situations exist, and a requirement has been established by the appropriate authority.

5.2.2.1.3 Aeronautical stations shall maintain a continuous listening watch on VHF emergency channel 121.5 MHz during the hours of service of the units at which it is installed.

ICAO standard and recommended practices ("SARPs") for international aviation activity are recommendations, but they are generally implemented in the national regulations by the member states.

406 MHz

121.5 MHz is being replaced by 406 MHz, as this is the frequency of the COSPAS-SARSAT organization. This organization provides a permanent monitoring worldwide through the use of polar orbit satellites augmented by geostationary satellite relays.

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    $\begingroup$ Couldn't say it better $\endgroup$ – dougal 5.0.0 Feb 19 '17 at 17:01
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    $\begingroup$ Fantastic answer that answers my question precisely. $\endgroup$ – heypete Mar 4 '17 at 23:03
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    $\begingroup$ On top of all this, a boat in trouble in the middle of the ocean would not likely try vhf unless there was a ship in sight, since it has limited range. There are a number of marine bands in the hf (shortwave) range which contain designated distress frequencies monitored by coastal stations, on which there’s a chance of being heard over long distances. But today, of course, one of the satellite communication methods would probably be best. $\endgroup$ – CCTO Dec 16 '18 at 2:15
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This answer is slightly offtopic for the aviation bit, but I believe it is useful to answer the question.

Marine VHF at 150-ish MHz is a local radio technology. It reaches the horizon, no further.

With an aircraft, the horizon can be hundred of miles away, due to the height of the aircraft. At 10000 m height, the horizon is approx. 350 km away. At 40 m (a reasonable height for antenna on a vessel), it's 25 km away. So while an aircraft at cruising altitude can use Line Of Sight-frequencies to communicate with another aircraft 600 km away, a vessel is restricted to 30-50 km distance on the very same frequencies.

A vessel in the midst of the ocean would not use VHF to send a distress signal. It may use VHF to communicate with rescue vessels within sight, to coordinate the rescue. To send a distress signal, it would use

  • Satellite communication systems
  • High Frequency Radio.

HF radio uses approx. 1.6M Hz to 30 MHz. The distress frequency is 2182 kHz. All ships above 300GT are required to listen to 2182 kHz:

In order to provide an effective link between the international radiotelegraph distress frequency (500 kHz) and the radiotelephone distress frequency (2,l82 kHz) all ships subject to the requirements for radiocommunications under the SOLAS Convention (basically this means cargo ships of 300 gross tonnage and above and all passenger ships) should be fitted with radiotelephone equipment and be required to keep a continuous listening watch on 2,182 kHz.

Whilst 2182 kHz probably does not have global reach, it can propagate as a ground wave well beyond the horizon. Other frequencies on the HF band, 20-22 MHz, may very well have a truly global reach, especially at night.

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