Actually compared to the huge number of planes that appear very, very few actually end up spotting my boat. Rather than dive every sighting I just make a quick course projection to see if it comes near enough to my position to raise concern. Usually the answer is no.
Unless of course i've done something nasty like sinking one of their ships in the area and they are activley hunting for me.
...and I imagine this might also change depending on the mod(s) one uses.
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