High Frequency (HF) radios are primarily used by large aircraft for what purpose?

High Frequency (HF) radios are primarily used by large aircraft for oceanic air traffic control communications due to their capability to transmit over long distances. HF radio waves can propagate beyond the horizon, making them suitable for communication in remote areas, such as oceans, where ground-based communication systems are limited or unavailable.

In the context of long-haul flights over vast bodies of water, HF radios allow pilots to stay in contact with air traffic controllers and receive vital information about their flight status, weather conditions, and routing guidance. This function is essential for maintaining safety and coordination during flight phases where other communication methods, such as VHF radios, would be ineffective due to range limitations.

While HF radios can also serve purposes like emergency communication, their primary utilization in large aircraft is geared towards ongoing, routine air traffic management over oceanic routes where VHF coverage is absent.