Dialing Up the Weatherman: Simplex Ain’t So Simple

When we fly, talking mostly with Air Traffic Control (ATC), we’re on a kind of party line — everybody’s on the same frequency, talking and listening — but when we’re talking to a Flight Service Station, well, it’s a bit different. In that case, only a few aircraft might be listening in.

FSS specialists are actually responsible for a very large area, but for us GA folks, that area is down low so, one frequency isn’t nearly enough (recall the limitations of VHF radio). At our regional Leesburg Virginia FSS, the FSS operators have dozens of possible frequencies that they could be listening on (in this case, about 75). Because of that, it’s important to use the proper procedures when using the ‘simplex’ mode — where you’re calling on the ‘receive’ frequency listed above the VOR data box on your chart, and listening on the VOR, using the ‘voice’ setting on your radio.

When I was a student pilot, I sure found this ‘talk on one frequency, listen on another‘ confusing. ‘What? You mean the ‘R’ means that the FSS is listening on that frequency, and I have to listen on the frequency of the VOR?’ Heck, until then I’d only been hearing Morse code on the VOR frequency. Then I found out this little trick also applies if you’re talking on an ‘RCO’ (remote communications outlet) on the ground, if you’re at an airport with a VOR having that same capability. By the way, if you’re talking to clearance delivery from a remote airport that gives you this option on a separate frequency, that’s actually called an RTR — a remote transmitter/receiver … not an RCO.

The Difference: RCOs are used to talk with Flight Service. An RTR is the term used when you do the same thing, but talk to ATC.

Minutia: Simplex — this is just a data communications term meaning, ‘one way, one channel’. Whenever you’re talking and listening on the same frequency, that’s duplex … but like all of aviation’s voice frequencies — and unlike the telephone — you can’t do both at the same time, so it’s actually called ‘half-duplex‘.

FREAKS … er, freq’s … and FLIGHT WATCH
There are a few exceptions to simplex procedures. Certain ‘universal’ frequencies, such as 122.2, or the few discrete area frequencies, do exist. One such is the Leesburg FSS, which uses 122.65 for the Shenandoah Valley. But most of all there is Flight Watch — less well known as Enroute Flight Advisory Service or EFAS … (Hint: spell it backwards.)

FSS frequencies are listed on aeronautical charts, as described above, but there are also separate sections in the A/FD. There’s a separate section about two-thirds into the ‘green books’ listing ARTCC and then FSS. In my copy they’re just before the preferred IFR routes. (If you use the ‘arrow’ index marks on the back cover, you can locate the ‘black bar’ pages underneath ‘ARTCC/FSS’.) They list each FSS area, its communication points (whether they’re VORTACs, VOR/DMEs, or RCOs), and if they’re simplex, either a ‘T’ (for if they transmit on it) or an ‘R’ (if they receive on it). And on the inside back cover, you will see a map of Flight Watch facilities. Such a deal…

ABOUT FLIGHT WATCH: Call up by singing out the facility name that you’re calling, or the nearest navaid, or just your general area, if you’re not sure. It doesn’t hurt to tell ’em what frequency you’re listening on, either. Although the name would give you the impression that someone is watching over you with radar, that’s not so. The radar they do have is looking at precipitation echoes — not airplanes.

These guys are who you’re gonna call for advisories on what the weather is doing further down your route of flight.

You talk and listen on the same frequency, just like when you talk to ATC, and it’s supposed to be available anywhere in the continental U.S. between 5000 MSL and 17,500 feet. Etiquette: When you’ve gotten what you need, reciprocate with what they need — a pilot report!

QUID PRO QUO: PIREPs are a very important part of the weather picture in our airspace, and they’re like the Red Cross and blood– they can’t have too much. Don’t be shy if you don’t remember the proper sequence from the AIM. Give them your aircraft type, position, altitude, and then bases, tops, visibility, precipitation, turbulence, ice — whatever else you can think of. You’ll help make his or her day … and maybe someone else’s. Don’t forget to precede your call with whatever FSS you think you’re near (e.g., ‘Leesburg Flight Watch’) or if you just don’t know, give the name of the nearest navaid. Fly safe and help the next guy. Simple rules, safer skies.