In 1927, the Ford Motor Company used the first of its Tri-Motors to fly auto parts between Chicago and Dearborn, Michigan. This is when a young Ford engineer, Eugene Donovan, developed and patented the “four-course, loop-type, low-frequency radio range,” the first radio aid to air navigation. The first two ranges were installed the following year at Chicago’s Lansing Airport and the Ford Airport in Dearborn. Both proved successful in guiding pilots during inclement weather and improving the reliability of cargo operations. It was the first time that pilots could navigate accurately from one place to another without ground reference or having to rely on dead reckoning, a form of navigation that seems to indicate the fate of a pilot who does not reckon correctly.
After extensive testing, the Bureau of Air Commerce began installing more than 400 radio ranges that crisscrossed the country and formed the civil airways that became known as the “radio-beam highways of the sky.” East-west airways were designated as green or red (Green 23, for example), and north-south airways were amber and blue.
The beauty of the system was its simplicity. The only airborne equipment required was an inexpensive low/medium-frequency receiver (200 to 400 kHz) with a coffee-grinder tuner and a pair of headphones. It rapidly became the backbone of the Federal Airway System until the early 1950s when the “omnirange” began replacing four-course ranges en masse. The last ranges were decommissioned by 1970 (although the one serving the airport in Chihuahua, Mexico, survived anachronistically into the 1980s).
Like VOR, the four-course range provided courses that led directly to or from a station, but that is where the similarity ended. VORs provide pilots with visual and thankfully silent guidance along 360 radials. Each four-course range had, well, only four courses, and using them for navigation required listening to a barrage of signals often punctuated with assaulting, ear-splitting static. Listening could be fatiguing. Although the “low-freq” radio range was not limited by line-of-sight reception as is VHF, reception range was limited by station power. Anyone ever having occasion to complain about VOR or GPS navigation has never used a four-course, low-frequency radio range.
Just as there are those whose passion compels them to build and restore antique airplanes, there are those who have a thing for avionics and early methods of radio navigation. David Frantz is a 54-year-old, 8,000-hour chief pilot for Airline Transport Communications and Navigation. He is so infatuated with the four-course radio range that he built one. It helps that he is an electronics engineer and used to be an FAA aviation safety inspector specializing in avionics out of Atlanta.
Frantz built an actual four-course range in Morrison, Tennessee (N35-37-30, W86-00-54). At the present time, you need a high-frequency receiver to hear Frantz’s four-course range on 28.210 MHz (the 10-meter ham radio band). On this frequency and with a power output of 100 watts, his range station can be heard almost anywhere in the world (depending on atmospheric conditions and time of day). He currently, though, is seeking approval to broadcast on 529 kHz, which is only 1 kHz below the commercial broadcast band. Because of the bandwidth of the station’s transmitter, however, you should be able to hear it when tuned to the lowest frequency on your AM dial (530 kHz).
Frantz’s radio range is online at “ Navigation in the 1940s: The Four Course Radio Range.” In this nicely produced, 10-minute video, Frantz takes you on an actual flight that completely encircles his four-course range. This allows you to hear all four quadrants (both A quadrants and both N quadrants). You also will hear the steady tone indicative of crossing each of the four, four-degree-wide range (on-course) legs. When flying in an A quadrant, you will hear the Morse code letter A (.-), and when in the N quadrant, the letter N (-.). The courses or beams are formed where an A quadrant overlaps an N quadrant to form a steady tone. The outbound magnetic directions of the four-course legs are 082, 172, 262, and 352 degrees.
Although this may sound like gobbledygook to those who have never used a four-course range, which likely is most of you, Frantz’s video makes range navigation a bit easier to understand. To those of you who have actual experience enduring the misery of “flying the beam” down to 300-foot minimums in the vicinity of an electrical storm, the video is a nostalgic return to a bygone era. In 1941, Parker Brothers, makers of Monopoly and other games, produced a board game called, Flying the Beam. It not only was fun to play, but the game made it easier for pilots of that era to learn how to use the four-course range.
To make things even easier, the Dean Radio Range Orientator was a clever in-flight aid used to help pilots orient themselves with respect to a radio range, an otherwise challenging and time-consuming procedure.
So if you happen one day to hear what sounds incredulously like the signals of a four-course radio range coming through your headphones, you are not in the Twilight Zone; you likely are in the vicinity of Frantz’s four-course range in Morrison, Tennessee.