AB9IL - Aeronautical HF Radio

Oceanic HF communications from a pilot's viewpoint.

Listening to Aeronautical radio is popular with a lot of short wave listeners, and there is plenty to hear as flights follow the North Atlantic or Pacific oceanic routes. Twice daily, Gander and Shanwick track and direct a barely subsonic herd of aircraft across NAT MNPS airspace. Between California and Hawaii, there is a constant stream of flights crossing each way, calling in position and weather reports to San Francisco.

Early in my short wave listening, I discovered the fascinating world of aeronautical monitoring and have been fortunate to be one of the voices. I flew the 757 and 737 for ATA Airlines, and it was a common task to make a crossing. Have a look at some photos and links that describe a pilot's experience flying across the oceans.

Before departing, we have a lot to do on the flight deck. Normal preflight checks are done, plus plenty of repeat-checking as it relates to the routing, weather, and fuel requirements. At ATA Airlines, 757 and 737 crews used a special Nav Checklist to cover the additional items required for ETOPS flights. For example, flights across the North Atlantic are given a "track message" specifying the routings prepared by either Gander or Shanwick. One of the pilots will plot those tracks on an oceanic chart, placing symbols to define the route to be flown, its "equal time point," and other information the crew may want to indicate geographically. Another particular ritual conducted at this time is the "route crosscheck." One pilot holds the flight plan, reading the waypoint names, distances, and courses aloud, while the other pilot verifies that data in the flight management computer is in agreement.

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 identifier of the track message 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.

Once, only once, did I receive the mother of all good clearances. It was on the way to Majuro, Marshall Islands. ATC picked up our transponder and cleared us to "cruise flight level three-five-zero and advise on the ground at Majuro...Bye Bye." Talk about a no-hassle arrival! We could descend when ready, fly the approach, and land - only keying the radio to advise starting the descent, and self-announcing near the (uncontrolled - tower closed) airport. In a nutshell, that is how aeronautical radio is used when a jetliner is flown over the oceanic routes.

Next, we will briefly discuss and display pictures ofthe HF equipment on most jetliners, and compare capabilities with amateur radio or SWL gear.

Next or Return to Index