[greenish_shores]

Not to nitpick, but polar flights can (and do, as a back-up, sometimes not only) use HF comms (which do not rely on a line-of-sight, as the waves are long enough to "bounce" off the ionosphere). It's slow (~300bps if transmitting data?), sometimes (but rarely) can have latency up to 15 minutes (interference from the Sun and others stars breaking/jamming comms for some short time, along other phenomenons), but it works. Even 15 years ago not every commercial airplane had satcom link installed, and even now, HF is the only thing which is required when flying away from VHF range. But anyway satcom is just more convenient usually (as long as it is available and it works).

On the other hand, I also think that some *ground* safety systems will rely on satellite data links as a back-up, as well.