For those of you who followed the departure from Guam, you might have heard a discussion between ATC and ZU-TAF asking them what com radios they have onboard.
Below is a very interesting post by Amateur Radio AB9IL with regards to HF communications.
After departure, the crew will call the HF radio facility for the first part of the ocean crossing and obtain the current frequencies and check the selective calling equipment. If you hear a carrier wave for a few seconds, followed by someone asking for frequencies and a SELCAL check, that is what is happening. Well before reaching the “coast out” point, the air traffic controllers will have conducted another procedure with the crew: issuing the oceanic clearance. ATC will read the clearance, and the pilot communicating will read it back, plus specify the numeric track message identifier received before departure. The routing, altitude, and Mach numbers are essential parts of the clearance, and both pilots normally write down what they hear from ATC. Note that the Central – East Pacific routes don’t use track messages; a simple IFR clearance is sufficient. About 150 to 200 miles beyond the coast, ATC terminates radar service and advises the flight to switch over to HF position reporting. The VHF radios are then set to 121.5 (guard), 123.45 (air to air), and the company ops frequency. Transponder code 2000 is set until re-entering radar controlled airspace. HF #1 is set to the primary frequency in use, and HF #2 is set to “DATA” mode. Then the flight makes plenty of data bursts for the HFDL monitors out there.
Note that there are some operators, with fat budgets, who use satellite communications, or a data-link system called CPDLC, don’t have to bother. with HF position reporting on oceanic flights. No fun for them…it reduces the experience of crowded HF frequencies to noiseless VOIP and text-messaging. Aside from communications, the work is similar for anyone doing class II navigation – regular checking of fuel burn, time estimates, upper air conditions, and the quality of on board coffee. There is a whole order and rhythm, as shown by example of the Nav Checklist. Crossing each reporting point, the pilot monitoring will turn up his communication panel’s HF audio gain, and call the facility working his geographic area, and make a position report (in standard non-radar format). This will be repeated until the flight is advised to make their next report to ATC on a VHF frequency nearing “coast-in.” The crew then sets the next VHF frequency in comm radio #1 and waits. Usually about 200 miles off shore, the ground based ATC signals start breaking squelch. Eventually, signals are strong enough to make contact with ATC, send a position report, and receive a code for the radar transponder. Radar tends to not make it as far as VHF signals, so a few minutes will go by before ATC advises “radar contact” and gives a domestic clearance to the destination.
*Thank you Corrie Basson for pointing us to this article
So, what Jean and James would have done is to contact an overflying airliner on their VHF radio and the airliner uses their HF radio for the long distance messages to Marshall Islands. The diagram shows the HF radio coverage of the Pacific.
