It's crowded out there, so understand what's expected.
Beyond approximately 200 nm from a land-based VHF communication station, HF radio is used as the main communication source for oceanic operations. A recent advance in communications technology allows reporting via satellite and communication over water via the aircraft's flight management system (FMS). This is accomplished using automatic dependent surveillance-contract (ADS-C) and controller-pilot data link communications (CPDLC). While this is the future of oceanic flight communications, currently only a few business aviation departments have this capability.
Most operators continue to use HF as their primary means of oceanic communication. The HF frequencies used en route are determined not only by the particular route flown, but also by atmospheric conditions and the time of day. Generally, lower frequencies are used during the night and higher ones during the day.
Each oceanic center has groups of HF frequencies assigned. These frequencies can be found in numerous resource locations, but most crews use the en route chart for the particular part of the world to pick up area frequencies. When receiving the oceanic clearance, the crew may request the “primary” and “secondary” HF frequencies. It is mandatory, while en route, that the primary HF be monitored.
There is a great deal of background/static noise on most HF radios. In the early days of oceanic flight, radio operators were used to maintaining HF listening watches. With two-pilot cockpits, that duty later fell to the pilot not flying the leg.
On first contact with the controller, the crew should perform a SELCAL (Selective Calling Radio System) check so the HF frequency does not have to be continually monitored by the crew. If the controlling authority needs to communicate with the crew, they will send a transmission through a ground-based encoder that is specific to that aircraft. An onboard alert tone and light will be initiated in the cockpit by the encoded signal thereby notifying the crew to reply.