Although the Low Frequency Radio Range system was heralded as a breakthrough, it was obvious that it was less than a perfect system from day one. Almost immediately starting in the 1930’s, development started on its eventual successor, the Very High Frequency Omnidirectional Radio Range (the “Omnirange” or VOR); which tackled the specific and real limitations of LFR. After successful experiments in 1939, a patent was filed by David G. C. Luck of the RCA Corporation in 1940. These far more advanced, interference free stations could support 360 radials or “beams” that could be visually followed. This provided far greater flexibility for the new Federal Aviation Administration or FAA (which would replace the CAA in 1958) to develop additional airways. A pilot could easily track a “beam” wherever he or, increasingly, she wanted and create their own customized routes.
The basic principle was this: 30 times a second each station sent an omnidirectional radio pulse followed by a directional beam that was swung around the full 360° like a lighthouse. The delay between the first pulse and second beam as seen by the aircraft was proportional to its bearing from the station. In more technical terms, a VOR has a frequency modulated (FM) 30Hz omnidirectional reference signal, which can also carry amplitude modulated (AM) Morse code ID and voice info such as the station name and hazardous weather advisories audible to the pilot. A second AM directional signal, which rotates every 1/30th of a second like the lighthouse beam, is synced to the reference phase as it passes through magnetic north. From the plane’s perspective, the rising and falling of the directional beam’s intensity as it whirls around appears as another 30hz signal that is delayed to the reference in direct proportion to the plane’s bearing , e.g. both signals are in phase due north, but are 90° out of phase due east, 180° due south, etc. – VOR measures this phase difference relative to desired radial. In theory, this system could provide an infinite number of radials, though its accuracy limited it to 360 nominal courses. VOR uses magnetic north as it always can be checked against an airplane’s magnetic compass.
When it debuted right after the Second World War, the system offered several other compelling advantages that systematically addressed LFR’s shortcomings:
In short: it was simply a much better system. It was made possible by the decreasing size and cost of increasingly complex electronics, first by mini-vacuum tubes during the war followed by the transistor in the 50’s and 60’s. Radios were now cheap and lightweight and even small general aviation aircraft were starting to have a full suite of communication and navigation radios that could take advantage of the new technology. Even the old, clunky radio compass evolved into the Automatic Direction Finder (ADF) by the 1960’s, which simply pointed the way to the “homing” or Non-Directional Beacons (NDB’s) with no effort on the pilot’s part beyond tuning the station. As with LFR, NDB's provided secondary support to VOR.
By this point the VOR was sorely needed: per the Air Transport Association of America’s 1951 “Facts and Figures,” the total number of US passengers flown that year was 13x of 1938, and carriers flew in one day all of the annual passenger miles flown in 1926. The annual passenger number would triple yet again by 1960. The aging, LFR defined airways groaned under this brutal surge in traffic brought on by post war economic prosperity and ever declining travel costs. Unrestricted by four beams, the VOR was used to create a new, much more expansive network of “Victor” or “V” airways, and above 18,000 feet the “Jet” or “J” routes with dozens of vertically separated flight levels - a role they still serve today.
There was an intermediate hybrid approach first demonstrated in 1941 called the “Visual / Aural Radio Range” (VAR) that used the same ILS equipment and frequencies that military and commercial planes were then increasingly equipped with. It was actually intended to be the original successor to LFR, but wartime radio component shortages stymied its rollout. It used interference-free VHF similar to a VOR, which also allowed for a more compact station size, but still projected four courses. The main difference was that while two opposing courses were “aural” and functioned like those of an ordinary LF range, the other two courses 90° to the first pair were visual. They were, in essence, a long-range localizer or the horizontal portion of the ILS, and the pilot read the same needle used during landing to determine if the plane was to the right or left side of course. One side was designated as the “blue” side that emitted a 150 Hz tone, and the other the “yellow” side that emitted a 90 Hz tone which the instrument read. They were marked on charts with a dark blue version of the LFR symbol, with the visual courses shown hatched instead of a solid shade.
This all would have been a decent upgrade in the early 40’s, but the same war that benched it also rapidly advanced the VOR’s VHF technology. Starting in 1944, the US still pressed ahead with 70 VAR stations, but their 4 courses were simply outmatched by VOR’s 360 easy to use radials. By 1949 the CAA had begun to describe them as “interim” facilities - all were pulled from service by 1960. Of note: VAR was widely adopted by Australia starting in 1947 as it was similar to their earlier Lorenz system, and would remain in service there until 1980.
VOR stations were first deployed in 1946 and their meteoric adoption was paralleled by the start of the Jet Age. The new 707, DC-8 and other jets carrying the newly branded “Jet Set” were in many ways easier for pilots to fly. For example, 4-engine propliners had sixteen touchy levers for throttle, mixture, propeller RPM and cowl flaps. Equivalent jetliners had a single set of just four thrust levers. However, they were also nearly twice as fast, covering 10 miles in a minute, meaning pilots had less time to complete their workload. Navigation had to be simple and easy for these pilots and they were the first main users of the VOR system. General aviation soon followed. In parallel, the military with its even faster planes adopted its own version called the Tactical Air Navigation System (TACAN) which used a higher frequency (960-1215 MHz) that provided greater accuracy and smaller station size (there are even mobile truck mounted units). These stations are often combined with many VOR stations as VORTAC’s and typically appear as a compact inverted cone on top.
Starting in 1955, the US began to install VOR along international routes for the benefit of its carriers. VOR’s ease of use and rapid deployment in the world’s largest aviation market would soon make it dominant worldwide. In the late 1950’s Britain’s Decca made a push to become a serious contender, even adding a scrolling map display, but VOR needed only a single station site to cover the same area as Decca’s four-station chains, had a lower receiver cost and, unlike Decca, was immune to precipitation static. In 1959 the International Civil Aviation Organization (ICAO) decreed VOR and DME would become the international standard. Eventually, over 3,000 VOR stations would be built worldwide.
VOR arrived with the modern and complimentary Instrument Landing System (ILS) which provided far more precise guidance to pilots landing in low visibility. Its promise was shown in 1929 and early Lorenz systems became common in Europe during the late 1930’s, but ILS only became truly widespread with the postwar age of smaller, more affordable avionics.
From the far end of the runway, ILS projects a 110Mhz vertical localizer beam down its centerline, and from one side of the runway a second horizontal 330Mhz glideslope beam, 90° to its plane - the actual frequency will vary slightly per each installation's assigned channels. Both beams intersect and define the glidepath, an imaginary line that extends along the centerline from the touchdown zone to a point ideally 3° above the horizon that aircraft follow on their approach in. Both are highly directional beams with right and left, and upper and lower sides respectively. ILS overlays a 90Hz and 150Hz tone on the carrier, and the localizer and glideslope antenna arrays phase shift both tones on each of these sides 180° opposite to the other. This causes each tone to perfectly cancel at the glidepath centerline but allows the 90Hz tone to be stronger on the left and upper sides of the path, and the 150Hz compliment to be dominant on the right and lower sides – the strength increases the farther one is from center. Via signal filters the relative voltage of each side pulls the horizontal up/down glide slope needle and left/right localizer needle to constantly indicate the relative position to the glidepath. ILS installations contain numerous signal and fault monitoring points. If the system detects a critical parameter falling out of tolerance it will automatically shut itself down.
As the design was finalized in the 1940’s, it was realized that by adding the glideslope needle to VOR's Course Deviation Indicator, and using its vertical course deviation needle for the localizer, it would be easy to visually fly an ILS approach with the same instrument by keeping both crosshairs centered. As described above, the Visual Aural Range also coopted the localizer needle. Marker beacons, evolved from LFR fan markers, provided a flashing light and audio tones to mark key distances, typically: an outer marker just inside the glideslope intercept (blue light and an audible series of dashes), a middle maker (yellow light with a dot-dash tone) where many aircraft would have to go "missed" if the runway wasn't visible, and sometimes an inner marker (white light with a series of dots) at the runway threshold itself. In recent years with the advent of GPS, many of these markers have been removed. An ILS backcourse can also be flown from the opposite end of a runway, albeit with no glideslope and "reverse sensing" by the localizer needle.
LFR provided the first instrument approaches, but they could offer only lateral guidance of 3°, about +/-300’ a mile from a station. If the station was located 3 miles to 5 miles from the runway, as was more typical for LFR approaches, this error could grow proportionally to 1,000’ to 1,500’ either side of the runway centerline. This limited LFR’s minimum descent altitudes (MDA’s) around 500’ to give pilots the necessary time and height above ground to line up for landing once they broke out of the clouds.
ILS provided the first true precision approaches. offering both lateral guidance accurate under ½°, or +/- 50’ a mile out, and even more precise vertical guidance of 1/7th°, or +/-15’ at this range. This lowered decision heights (in essence, the same as an MDA but a specific term to ILS) to 200’ for Category I ILS approaches for even small aircraft. With specially certified equipment and aircrews, this can be further lowered to 100’ for Category II approaches. Starting in the frequently fogged-in UK in 1964, ILS guided autopilots began to “autoland” larger aircraft in zero visibility Category III conditions. When combined with radar, this greater accuracy meant that several aircraft could be easily separated on same ILS approach, and only the densest weather threatened airport operations, increasing available capacity and reducing delays and cancellations.
ILS’s potential was first demonstrated with the Diamond-Dunmore system developed by its namesake Bureau of Standard scientists who were also behind the development of the US Government’s first LFR Stations. Its 330 kHz localizer was similar to an LFR beam but, instead of dots and dashes, each side carried a slightly different aural tone at 65Hz and 86.7Hz. This was read by a dual vibrating reed indicator (also proposed but rejected for LFR) that showed the side the signal was strongest. Marker beacons alerted the pilot to start their descent when 5 miles out and when the runway threshold was crossed. Doolittle used these components to land successfully at the end of his historic “blind” flight in 1929. By 1930 the system added a simple “up” and “down” ammeter that provide crude altitude guidance based on the overall strength of a third 93.7 kHz “landing beam” signal. Marshall Boggs made the first blind landing with its added vertical guidance at the Bureau’s College Park, MD testing field in 1931, and Albert Francis Hegenberger relied on it when he became the first pilot to blindly fly solo, point-to-point, in real world instrument conditions in 1932.
By 1934, the German company Lorenz A.G., then also a subsidiary of American owned International Telephone and Telegraph (ITT) incorporated similar features to its beam - notably after the Bureau’s work was published - increasing the frequency to 33.33MHz for better accuracy and adding other refinements. Like LFR, Lorenz started as a primarily aural system, but later versions used a visual needle that rhythmically “kicked” toward the beam, along with a vertical ammeter and marker beacon lights. It was installed at dozens of runways throughout Europe and the rest of the world by the late 1930's. However, as the altitude guidance for these early systems was based on signal strength, the resulting glideslope was parabolic as this was a function of the inverse square of the distance. This required a steeper descent at the start of the approach which had to be shallowed just before landing - not ideal, especially for larger planes. Also, in an era when many aircraft were just adding one radio on board, both systems required additional receivers and equipment and were thus generally restricted to the larger military and commercial planes that could afford them (only 200 aircraft were Lorenz equipped by 1937)– wider use would have to wait.
In 1937, Lorenz experimented with adding a second transmitter, turned 90° to the ground and pointed a few degrees above the horizon, to define a straight glideslope a pilot could easily follow at a constant rate of descent. This, along with Lorenz’s commercial success, caught the attention of the CAA. Later that year, with ITT’s assistance, they formed a committee to test it and other systems in Indianapolis and to create a new standard based on their best features. By 1938 it delivered the new “Indianapolis” or “CAA Instrument Landing System” that also featured a straight glideslope. It successfully brought down a commercial flight in a Pittsburg snowstorm that January and the CAA authorized installation at six airports by 1941. War would forestall further civil development, but the US Army Air Corps continued to work with CAA and ITT engineers to refine the system, again increasing its radio frequency for better accuracy and static resistance, and developing truck mounted units for field use. By 1945, it perfected its Set Complete System or SCS-51 specification which became and remains the current standard for ILS. It worked well: by 1947 the CAA agreed to also adopt it for US civilian aircraft, and by 1949 it was adopted internationally.
The last piece to be developed were the approach lighting systems that provide a string of strobes and other bright lighting ahead of the runway to help aircraft transition from instrument flight in the murk to a visual landing. The US Navy in concert with several airlines developed the modern basics at the Arcata / Eureka experimental naval station purposely built on the fogbound Northern California coast by 1947. By 1956 New York’s Idlewild (later JFK) would be the first major airport so equipped. As with VOR, as transistorization dropped the size and cost of its electronics, ILS’s ease of use and accuracy pushed LFR and remaining Lorenz approaches to extinction by the 1960’s.
VOR’s ability to create far more flexible, reliable and higher capacity airways would become critical in the postwar period as the skies rapidly filled with increasing numbers of faster moving aircraft. However, a tragic series of accidents between 1956 and 1958 would showcase how dangerously outdated other aspects of the pre-war airway system had become. They would serve as a catalyst of reform that would both cement VOR’s role and ensure the complete obsolescence of the Low Frequency Radio Range.
The first and most infamous incident, the June 1956 Grand Canyon Mid-Air Collision, highlighted two major vulnerabilities: both flights were not in direct contact with ATC and radar still wasn’t available in most areas. 128 lives were lost as a United Airlines DC-7 and a TWA Connie converged maneuvering around clouds. Military and civilian aircraft still commingled using separate ATC systems and this proposition increasingly proved disastrous. In April 1958, United Airlines 736, yet another scheduled DC7 “on airways” outside of Las Vegas, was struck by an errant 2-man Air Force F100 Super Sabre jet fighter on a training flight. Both were in contact with their respective ATC facilities just 6 miles apart that had no way of communicating with each other. All 49 persons on both aircraft were lost. Aviation Week commented that the collision was “another ghastly exclamation point in the sad story of how the speed and numbers of modern aircraft have badly outrun the mechanical and administrative machinery of air traffic control.” By June 1958, these two accidents and three other high profile fatal collisions would bring a total death toll of 245 persons. The CAB later determined that 159 mid-air collisions occurred between 1947 and 1957 and there were 971 near-misses just in 1957 alone.
Public reaction was fierce and congressional hearings were already well underway after the Grand Canyon incident when the United 736 collision occurred. One senator lamented “one-half of the air traffic of the nation is military, the other half is civilian: and the right hand doesn't know what the left hand is doing.” Congress was compelled to quickly act: in August, it passed the Federal Aviation Act of 1958. The outmoded, prewar CAA was replaced by the new, independent Federal Aviation Administration created for the Jet Age and endowed with broad authority over both military and civilian flights. Given a clear safety mandate, it would soon spend $250 million ($2.2 billion in 2020 dollars) modernizing its operations, including integrating radar, computers and improved navaids. Controllers could now finally talk directly to their aircraft over a dedicated radio network, which they increasingly tracked on phosphorescent green radar screens instead of manual plotting tables. Finally, by 1962, the Continental Positive Control Area was established where all aircraft above 24,000’ (later lowered to 18,000’) had to be in ATC contact on approved IFR flight plans.
VOR, especially when combined with DME, allowed the FAA’s newly empowered controllers to guide far larger volumes of well separated traffic with greater flexibility and precision unimaginable with LFR - and nearly to the runway threshold with the increasing adoption of ILS. VOR's role was reaffirmed in the 1960’s when the FAA systematically upgraded its first-generation vacuum tube radios and mechanically spun antennae to reliable solid-state electronics with fixed phase arrays. Although Non-Directional Beacons would still deemed useful for a few more decades, LFR had no place in this future.
And so it was against this seismic shift that LFR saw its sunset. A 1954 Air Force flight instruction manual had already described the LFR system as “antiquated,” only 25 years after its debut. The government had begun decommissioning stations in 1952 and by 1960, the number fell 42% to 245. As always, price prevented many operators and pilots from initially upgrading, but by the 1960’s cheaper transistorized electronics would eliminate this objection. As their low-frequency radio waves did a great job of bending over terrain, LFR had a longer life in some mountainous areas. But even this small advantage did not prevent the last US station being pulled from service in Northway, Alaska in September, 1974. Canada shut down its last range at Crescent Valley (Castlegar) in May, 1981 and in its last few months, it was only ever activated on pilot request. One source stated many aircraft flew in from all across US and Canada to fly its beam one last time before it was decommissioned. The last station in the world reportedly shut down in the mid-1980’s in Chihuahua, Mexico.
VOR, ILS, positive airspace control and the other changes implemented by the FAA were duplicated throughout the world in the 1960’s and 70’s. But, technology continued to advance. By the late 1970’s it appeared ILS would be replaced by Microwave Landing Systems (MLS), which used a 5GHz frequency that offered pinpoint accuracy and wider coverage that also allowed curved approach trajectories. However, by the 1990’s it was clear the true challenger to ILS and VOR was Satellite Navigation (first with GPS, then Glonass, Beidou and Galileo with more scheduled) that provides far greater accuracy utilized with Area Navigation (“R-NAV”) techniques that are becoming the standard for aircraft navigation. These are much easier to use (e.g. your location is simply shown on a moving map just as in a car), and there are no signal range or coverage gaps with the omnipresent signals from the sky. By the early 2000’s it appeared VOR and ILS were in the same position LFR was in 50 years before. By the 2020’s though, increased awareness of how vulnerable satellite systems are from everything from solar flares to selective shutoff due to geopolitical events have caused many nations to reconsider the role of these ground based legacy systems. The US now plans to maintain half of its current 967 VOR stations as a “Minimal Operational Network” for backup. The Air Force and Europe have also begun to invest in “NextGen” ILS systems that have tighter beams and reduce interference effects from nearby buildings.
It’s interesting to note that 80 years after their implementation, both VOR and ILS remain relatively unchanged and it now appears both will still have another few decades of service to come: a testament to their original engineers. Due to their cheapness and low maintenance (basically, a simple transmitter with a vertical monopole antenna) many Non-Directional Beacons persisted to this day - especially in remote areas. As of 2020 a few old converted LFR sites remain in use as such after almost a century of service. However, VOR’s new role as the secondary backup to GPS has now rendered NDB’s fully obsolete. They were removed from FAA pilot instruction in 2015 and the United States and many other countries plan to pull most remaining stations from service by 2030.
As discussed, the advent of the VOR made the old Low Frequency Radio Range stations obsolete practically overnight. In flipping through old aeronautical sectional maps from the 1950’s and 60’s, one can see the familiar blue VOR compass roses multiplying like rabbits as the old magenta range symbols faded away.
There were no constraints to the placement of the VOR’s that defined the high-altitude Jet Routes, but the ones that established the lower altitude Victor routes generally followed the old LFR network – many just simply coopted the old station’s name. It would have perhaps seemed logical to reuse the old LFR sites for the new stations, but this rarely, if ever, occurred for two reasons. The first was that, as discussed above, VHF required that VOR’s instead be placed at higher elevations or at more open sites that had a direct line of sight to aircraft. The second was that to ensure uninterrupted navaid service, the old station would remain in operation “as is” until the new VOR was fully commissioned - sometimes right next door. There was often an overlap in service before it was shut down. A few other LFR stations kept their center antenna and lived on as Non-Directional Beacons, and some of these have survived to this day after eighty years of continual service. Other sites were logically repurposed into another type of commercial or government radio facility. But in the end, most sites were disposed of.
As stations started to be decommissioned in 1952, in most cases the government removed the equipment, antennae and sometimes the blockhouses (leaving the foundation pads) as made clear by the stations that started disappearing from aerials during the late 1950’s through the 1970’s. More than a few blockhouses survive to this day on now unused lots - some abandoned and rotting away, others repurposed as various types of outbuildings. On aerials they are frequently belied by their 45° orientation on their lots toward absent antennae. At completely cleared sites, the distinctive scars marking former blockhouses, antennae and access roads were often visible decades later on aerials, a few even today. In other cases, the FAA offered the new owner / landlord a check to simply walk away and leave everything “as is." This latter instance appears to explain the two very well-preserved California stations at Whitmore and Fort Jones, and quite possibly the stations at Lawson, Georgia (actually in Alabama) and Whiting AFB, Florida. In far out areas, the salvage value of a station couldn’t offset the cost of hauling it off, and many remote stations in Canada and Alaska had their transmitters removed with the rest just left standing in the wilderness. A few such as North Shore AK and Fort Chimo QB appear to still be mostly intact in aerials.
In urban areas, the stations that were once built comfortably on the outskirts of cities and towns in the 1930’s and 1940’s were now multi-acre parcels of appreciating land in the way of rapidly growing suburbs, and as such, many were redeveloped. In some cases though, the original legal parcel survives “telegraphing” its legacy through its impacts on new buildings. Federal law requires that public uses have the highest priority in surplus land sales, so many sites became parks (baseball fields are common) or part of a freeway right of way. That said, through the quirks of selective land use, the remains of a surprising few survived.
Rural areas typically provided the best opportunity for something to remain of the old stations. Farmland leased to the stations was usually quickly reclaimed, cleared and ploughed under to be reused. However, the foundations of some sites were left in place and can still be seen on aerials. Even in the countryside, redevelopment claimed many sites, more were completely overgrown by vegetation and river/shore changes have obliterated others. However, trees and shrubs still trace out the original boundary lines of many former sites. Of interesting note: there are a few rural locales that still have a “Radio Range” road that once served a station now long gone for decades.
Our Map Page covers our extensive census of LFR sites throughout the world. As can be expected with a system last used over half a century ago, much it has already disappeared. Of the 875+ sites we’ve identified - roughly speaking - something is left at only 40% of the sites, no trace is left at another 38% of sites, and 22% of sites (mainly outside of North America) still can’t quite be positively geolocated and have their current status determined. Of the 40% where something remains, it is only really substantial at half of these sites or 20% of the total number. Only a handful of LFR stations could still be described as “intact” and almost all of these are located in truly remote locations which is also the likely reason they survived.
After reviewing nearly 700 Range Station locations in North America, it appears that there are just four station sites that have been something left of the original station and are readily accessible to the public:
There are dozens of other sites where LFR remnants can be found, but they are on either private property or public property / parkland where access may be restricted. Please obtain clear permission from the owner / relevant authorities before attempting to access these sites – do NOT trespass!
Outside of these sites, there are three museums that, as of 2023, have permanent, dedicated exhibits relating to the Low Frequency Radio Range:
Short answer – not much, if any. Although I obviously have some interest in this subject, I acknowledge that this a fairly esoteric topic that’s not front and center in most people’s minds. In addition to this view, there are a number of factors that have and will continue to stymie preservation efforts of LFR sites and related equipment:
That said, I’ll throw out my hope and my wish that something more will be preserved for future generations. I think the best opportunity would be at site still located on an airport property, park or other open space (e.g. land already used for something else compatible with the display) near a reasonably sized urban area that could drive visitor traffic. Ideally, it would be close enough to an established aviation museum to take on and curate, and the site could potentially be used as additional outdoor aircraft display. If the antenna towers from an older site can be found somewhere, moved from a less accessible site or replicated and restored along with a blockhouse, this could be a good way of preserving this piece of aviation history.
If anyone one has any ideas are knows a group that may be interested, please message me.
Although he filed the patent for the dominant radio navigation system that has guided air traffic worldwide for decades, Dr. David George Croft Luck gets little notice today as the nominal inventor of the Very High Frequency Omnidirectional Radio Range (VOR). His draft card and census records available via Ancestry.com reveals that he was born July 26, 1906 in Whittier, CA to English parents. He would go on to attend MIT and would become a research fellow there after getting is B.S. in 1927 and Ph.D. in 1932. Picked up by RCA Victor that year, he would continue his work in their Laboratories Division which ultimately lead to the development of the VOR by 1940, along with other radio innovations he would patent. VOR was first tested at the CAA’s Indianapolis Experimental Station in 1941 where ILS and civilian radar were later tested, and was rolled out nationally starting in 1946. His efforts ultimately led to his receipt of the Pioneer Award from the Institute of Electrical and Electronics Engineers (IEEE) in 1954. Per Social Security Records Dr. Luck passed away in 1994 in Santa Barbara, CA at the age of 87. If anyone has any additional information that can fill out the story of this man, please reach out to me.