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This answer has inspired me to a question: say you are a castaway on a desert island. There might be a plane flying casualy but you can miss it. So you want to create some pattern (e.g. put some branches in the sand near the beach) which will signalize S.O.S. to the pilot.

Are there any simple, international, emergency patterns for this purpose?

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  • Just make sure you don't write "HELF". – Erik Sep 16 '16 at 19:42
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The trick is, high contrast, right angles, and unnatural colors. A ratio of 6:1 for the lines. Letter X or V are best.

So, if you find two 6 foot long, one foot wide branches, place them in an X. Scale as you can to get it as large as possible.

Source: Wilderness First Aid Field Guide.

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    what is the ratio for? – Jay Bazuzi Jan 28 '12 at 7:30
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    @JackBazuzi: Easy visibility. A bit wider is okay, narrower not as well. – PearsonArtPhoto Jan 28 '12 at 14:11
  • I mean, what are you measuring with the 6:1 ratio? Also, Jack is my father, ha ha. :-) – Jay Bazuzi Jan 28 '12 at 18:23
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    Oh. The length of the part of the letter to the width of the letter. IE, for the X, you ideally would want something for each line in the X that is 6 feet long, 1 foot wide, roughly. Of course, bigger is better, so... – PearsonArtPhoto Jan 28 '12 at 19:57
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The international distress signal is a triangle of fires.

enter image description here

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    THanks, but if you are on the desert island weeks and months, you cannot burn fire all the time. And making triangle from just wooden things isn't very onspicuous I think. Any static pattern that can be very flagrant? – Tomas Jan 28 '12 at 0:31
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    @Tomas: well you can fire it when you see a plane: you just have to pay attention, but it seems a reasonable request to a castaway – clabacchio Jun 16 '12 at 16:13
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There is actually an international standard for this: The Chicago Convention on International Civil Aviation, and in there Annex 12 – Search and Rescue, appendix 2 "Ground-air visual signal code". Quoting it:

2.1. Ground-air visual signal code for use by survivors

Ground-air visual signal code for use by survivors

[…]

2.3. Symbols shall be at least 2.5 metres (8 feet) long and shall be made as conspicuous as possible.

Note 1.— Symbols may be formed by any means such as: strips of fabric, parachute material, pieces of wood, stones or such like material; marking the surface by ramping, or staining with oil.

Note 2.— Attention to the above signals may be attracted by other means such as radio, flares, smoke and reflected light.

So it would be the "V" for the case of the castaway, or "X" as the more urgent distress signal if there is indeed a need for medical assistance. And if (s)he sees the aircraft rocking its wings (or at night, flashing its landing lights twice), that's a good sign … it means the pilot saw and understood. (Specified in the same Annex 12 document as linked above.)

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  • This is great, but I wonder: is this something that all pilots learn as part of their training? That is, can you guarantee that all pilots will understand this on seeing it (especially the V)? +1 – Loduwijk Nov 12 '18 at 16:49
  • Also (and this isn't on you... I realize you didn't write it), isn't 8 feet going to be visible only to nearby, low flying aircraft? If it is high, far, or both I would guess that you would need much more than 8 feet to be visible at a distance. Having trouble finding actual data on this, but doing some quick estimating and calculating I'm guessing I might be able to make out a 10 foot V at a mile, maybe 2, but probably not much more than that. This might be sufficient for a search and rescue plane looking for you, but we're talking casual, accidental discovery. – Loduwijk Nov 12 '18 at 17:16
2

SOS is pretty recognizable and clear. Just make it BIG. Rocks with holes around them (to create contrast) seem to be the easiest and best way.

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