Originally Posted by
michael0658
The radio horizon at 35,000 ft is about 230 nm for a ground ATC. At its last reported position, this plane was beyond the Line of Sight (LOS) radio horizon for all ATC systems and ground radio.
For VHF/UHF I agree. For HF comms, there should have been much longer range/coverage. Question is, was there any guard channel on HF, in that part of the globe, that would been monitored.