The Impact of Navigation Aid Systems on Air Force Real Property Requirements


Copyright 1998, Scott D. Murdock

(Updated in August 1999 to include figures as separate scanned images)

(From a report submitted to Embry-Riddle Aeronautical University in 1996)







    Radio Range

    Radio Beacon

    Very High Frequency Omnidirectional Range (VOR)

    Instrument Landing System (ILS)







Table 1 - List of Air Force Bases Studied

Table 2 - Timetable of Navigation Aid Systems Real Property Use

Table 3 - Timetable of Barksdale AFB Navigation Aid Systems


Figure 1 - Graphic Timetable of Navigation Aid Systems Real Property Requirements

Figure 2 - Aeronautical Chart showing the Barksdale AFB area, dated February, 1948

Figure 3 - Aeronautical Chart showing the Barksdale AFB area, dated April, 1993

Figure 4 - Barksdale AFB Navigation Aid Systems


The purpose of this paper is to evaluate the impact of navigation aid systems on Air Force real property requirements. It will use real property needs (leased or purchased sites or annexes separate from the main base) to trace the evolution of navigation aid systems used by the Air Force (including its predecessors Army Air Forces and Army Air Corps).

The period chosen for study is from 1938 (the earliest data located) until 1974 (the closing date of the most detailed reference available; Mueller's 1982 work). Air Force history programs center on units, not installations; this makes historical information on real property holdings somewhat scarce and inconsistent in its availability and depth of coverage.

The writer selected 20 bases for study based on availability of data within existing research files. This gives a sample which is not random, but which the writer believes, based on extensive research of the history and design of Air Force installations, to be representative of all Air Force bases.

This paper will show how the type of navigation aid system influenced needs for additional real property off the main installation. It will show how these property needs have changed over the years as navigation aid systems have changed. It will then show some of these navigation aid sites were disposed of after systems became obsolete, some have remained in use to the present day, and some remain in use by the Federal Aviation Administration.


To put this paper into proper historical context, we should consider that in the earliest years of military aviation, there were no navigation aids. Over the years bonfires, lights, and then radio and radar systems were created to fill the need for accurately guiding aircraft from one airport to another.

As these newer systems came into being, their establishment required real estate. In many cases, the necessary locations were not within the confines of the installation, requiring additional parcels of land be leased or purchased. These off-base locations are referred to, generally, as "sites" or "annexes" and are under the jurisdiction, accountability, and control of the main base.

This paper stems from the writer's interest in Air Force real property holdings, and a curiosity about the many type of navigation aid sites encountered in years of researching off-base sites.


Listed below are the most common types of navigation aid systems encountered in the available documentation on the subject bases. I have excluded less common systems such as obstruction lights, horizon lights, flash beacon lights, Long Range Navigation (LORAN) stations, Short Range Navigation (SHORAN) stations, and Tactical Air Navigation Systems (TACAN). These systems were only occasionally found in the data available; indicating they were either not in common use or were situated on the main base with no need for additional real property.

To make things more interesting for the researcher, one system in particular (Instrument Landing System Middle Markers) has often been situated on off-base sites very close to the base boundary. Some of these have been disposed of by merger with the main base. In other words, additional land was acquired to enlarge the base perimeter to encompass the ILS Middle Marker site.

Radio Range. This system is also called a "four-course radio range" or "A-N range" and was first installed by the federal government in the late 1920s (Nolan, 1994). By 1933, 90 of these radio ranges were operational (Illman, 1989). They were the standard navigation aid system until the 1950s. By the early 1950s nearly 400 ranges were operational; by 1957 about 88 were still operating, primarily for military use (Zweng & Dohm, 1957). The radio range is typically located 2 or 3 miles (sometimes farther) from the airfield; down wind for the prevailing bad weather wind direction (Day, 1938).

Transmitting to an Amplitude Modulation (AM) receiver in the airplane, the radio range provided pilots with four on-course legs, or "beams," to fly. Flying any of the four on-course legs would give the pilot a continuous tone, formed by overlapping A (dash dot) N (dot dash) signals. The pilot would know if he was flying toward or away from the station by the increasing or decreasing volume of the transmission (Illman, 1989). The northern-most and southern-most quadrants would give the pilot only an N Morse code signal; the eastern-most and western-most quadrants would give only an A Morse code signal.

From the real property perspective, a radio range needs to be aligned from the main base as described above, and be in a fairly open space to allow unhindered radio transmissions. Although it has been inactive for over 35 years, the five antenna poles of the Randolph radio range are still in place, as observed by the writer in June, 1996.

Radio Beacon. This category includes different types of beacons; they bridge the gaps between other systems (Very High Frequency Omnirange, Instrument Landing System, etc.).

The first type is the Marker Beacon. These were low-powered beacons transmitting a distinctive code, and were installed along the on-course legs, or beams, of radio ranges (Nolan, 1994). This type of beacon was shown on sectional charts as either a football-shaped or figure eight-shaped pattern, and was also known as a fan marker beacon (USCGS, 1944) or a fan type marker (Kay, 1938). This type of radio beacon was used up until the 1950's.

Next is the Nondirectional Radio Beacon (NDB) which transmits a uniform signal in all directions. By using a Direction Finder (DF) or Automatic Direction Finder (ADF) receiver, a pilot can determine the airplane's bearing from the NDB. First appearing in 1924, nearly 300 were in use by 1964. These were used for en-route navigation on the colored (RED-64, GREEN-32, etc.) airways up until about 1965. However, lower-power NDBs continue in use as instrument approach aids at smaller airports. Over 600 were in use by 1985 (Nolan, 1994). This type is also known as a homing beacon or a homer (Heflin, 1956).

Very High Frequency Omnirange (VOR). This new type of range became the national civil navigation standard in 1946. It had two major advances over the older radio range. First, it had 360 usable navigation courses instead of four. Second, it operated in the Very High Frequency (VHF) range, which made it far less succeptible to static and reflected signals than its predecessor (Nolan, 1994). The VOR installation program was completed in the mid-1950's and completely changed the pattern of radio navigation (Zweng & Dohm, 1957).

In the airplane, the pilot selects the chosen course, or radial, on the VOR equipment. The equipment will show if that course will take the airplane to or from the VOR; and will also indicate deviation from this course (Nolan, 1994). The VOR system is used for the victor airways (V-18, V-94, etc.) which are still in use today (NOS, 1993). VORs are divided into three types based on their power and purpose. Low-altitude VORs are useful up to 40 miles away and 18,000 feet altitude. High-altitude VORs are useful up to 130 miles away and 60,000 feet altitude. A Terminal VOR (TVOR) is useful up to 25 miles away and up to 12,000 feet altitude. It is only used as a local approach aid to an airport.

The VOR does offer a challenging real property situation. A clear zone of several thousand square feet around the VOR is necessary for the signal to transmit properly. Tall buildings thousands of feet away can distort the signal (Nolan, 1994). This is reflected in real property requirements. For example, the Barksdale AFB TVOR: although the site itself is a small building on a 3.68 acre site, a total lease of 288.5 acres was obtained for this site to assure a clear zone (S.W. Div., 1960).

Instrument Landing System. This system provides the pilot with vertical and lateral guidance, allowing an approach path directly to the runway. It uses three types of transmitters: the localizer, the glide slope, and marker beacons. The localizer and glide slope transmitters are typically within 1,000 feet of the runway; this means that they will almost always be found on the main installation. Of interest to this paper, however, are the marker beacons. The inner marker is usually located 3,000 feet from the end of the runway, and the outer marker is located 4 - 7 miles from the end of the runway (Nolan, 1994). This means the middle marker may be on the main installation or may be on an off-base site; the outer marker will be on an off-base site.

As mentioned in the introduction to this section, the middle marker sites, due to their closeness to the main base, occasionally start as off-base sites and are later annexed to the main base by the lease or purchase of additional real estate. Looking at the Barksdale ILS Middle Marker Annex, it is a separate site approximately 350 feet away from the perimeter fence of the main base (S.W. Div., 1970). An additional parcel of land, about .5 acre in size, could connect the site directly to the main installation. This would allow access to the site directly from the end of the runway; instead of the present condition which is a to drive off-base, travel through a housing development, then through a gate and down a dirt road to the site. This site was in use for many years, leading the writer to wonder why this additional land was not acquired for convenient access.


To better see this relationship, data on off-base navigation aid sites was researched on a sample of 20 installations. Table 1 shows the Air Force Bases studied. Lack of available data forced a non-statistical sample; but the writer believes these bases are a fairly typical mix.

Table 1 - List of Air Force Bases Studied

Altus Air Force Base Altus, Oklahoma
Barksdale Air Force Base Bossier City, Louisiana
Bergstrom Air Force Base Austin, Texas
Carswell Air Force Base Fort Worth, Texas
Castle Air Force Base Merced, California
Craig Air Force Base Selma, Alabama
Dyess Air Force Base Abilene, Texas
Goodfellow Air Force Base San Angelo, Texas
Griffiss Air Force Base Rome, New York
Keesler Air Force Base Biloxi, Mississippi
Loring Air Force Base Limestone, Maine
March Air Force Base Riverside, California
Mather Air Force Base Sacramento, California
Maxwell Air Force Base Montgomery, Alabama
Norton Air Force Base San Bernardino, California
Randolph Air Force Base Universal City, Texas
Scott Air Force Base Belleville, Illinois
Vance Air Force Base Enid, Oklahoma
Webb Air Force Base Big Spring, Texas
Westover Air Force Base Chicopee, Massachusetts

The sites associated with these bases were coded into the types discussed in the previous section. As closely as available data allowed, first and last dates of use were determined and are shown in table 2 and figure 1.

Table 2 - Timetable of Navigation Aid Systems Real Property Use

Radio Range 14 1950 1970
Radio Beacon 14 1955 1965
Very High Frequency Omnirange 22 1955 1970
Instrument Landing System (ILS) Middle Marker ** 4






ILS Outer Marker 21 1955 1980
* Dates are rounded to the nearest 5-year point for ease of portrayal.
** Four of these middle marker sites were annexed into the main base by acquiring additional land--literally changing the site from off-base to on-base. The first dates are for the four annexed sites; the second dates are for the nine sites that remained off-base.

This was not a simple, definitive task, as the site may be on real property records prior to the system's activation, and may remain on real property records long after the system's inactivation. Also, many of the sites investigated were redesignated during their existence, and the dates of these redesignations have not always been accurately reported in historical references. This does limit the accuracy and reliability of the data, but the writer believes it is still valid enough to show general trends.


Since the writer had access to more detailed information on Barksdale AFB, this will serve as a case study of one particular installation. Barksdale AFB currently has a TACAN and two ILS systems (Defense Mapping Agency, 1996). All the components of these systems are located on the main installation. Over the years, Barksdale has had a radio range, a marker beacon, and a TVOR; all were off-base. Barksdale AFB has had two off-base instrument landing systems; the earlier system had a middle marker and an outer marker Northwest of the main base, the later system had a middle marker Southeast of the base. The former radio range site later served as the Southeast outer marker site; it was redesignated as a radio beacon annex in 1958. An item of interest to the researcher: the Barksdale AFB TVOR was transferred to the Federal Aviation Administration in 1968 (Mueller, 1982) and is still in use as the Elmgrove VORTAC (NOA, 1993). Table 3 lists the various Barksdale AFB off-base navigation aid sites.

 Table 3 - Barksdale AFB Navigation Aid Systems

Radio Range *, ** 11.25 1944 1989
Radio Beacon (Fan Marker) .28 1945 1962
Terminal VOR 288.50 1957 1967
ILS Middle Marker (Old) .51 1943 1954
ILS Outer Marker (Old) .23 1943 1954
ILS Middle Marker (New) * .13 1956 1989
* Although the navigation aids have long been inactive, these two properties are still on the real property account of Barksdale AFB, pending disposal action.
** This site was redesignated as a Radio Beacon Annex in 1958. This site then served as an outer marker site in conjunction with the ILS Middle Marker (New).

Figure 2 shows the Barksdale AFB area as it appeared on a 1948 sectional chart.  Figure 3 shows the same area as it appeared on a 1993 sectional chart.  The 1948 chart shows the radio range and fan marker beacon.  The 1993 chart shows the former TVOR site (now an FAA VORTAC).  Figure 4 charts the chronology of the sites.


The writer hesitates to draw any wide-ranging conclusions from this project; for the three following reasons.

First, data concerning the use of off-base sites is somewhat scarce and difficult to acquire. The only published, comprehensive, works provide at best a superficial coverage of this type of property. Comprehensive information would need to be carefully sought out from documents of the primary installation supporting the site. Other non-published sources such as the Army Corps of Engineers, the Air Force Historical Research Agency, the Air Force Real Estate Agency, and local seats of government may need to be consulted.

Second, available data offers certain questions as to its accuracy. For example, in the sample database used there are 237 dated records. The events captured on these records took place on 132 different dates, yet 13 records are dated December 28, 1955. These 13 records are from sites supported by six different main bases. The writer suspects, but has no evidence to confirm, that this may have been due to a policy change in the method of accounting for real property which became effective on that date. In other words, some sites may have existed before that time but were not inventoried or reported as off-base sites.

Third, the available dates represent primarily the real property transactions (activation, redesignation, inactivation, etc.). These dates may be years away from the dates of operational use of the supported navigation aid system.

The writer recommends using this data for only the most general estimations of navigation aid service dates. Without installation-specific data, any Air Force-wide conclusions are probably not accurate enough for serious research. On the other hand, when studying a specific installation, the thorough gathering of data from the various sources mentioned above could result in a useful information about that particular base.


This paper described four types of navigation aid systems likely to situated on off-base sites; the radio range, radio beacon, VOR, and ILS marker beacons.

Using a sample of 20 Air Force Bases, off-base navigation aid sites were researched and compiled in a database. Approximate dates of use were charted to look for trends in navigation aid use.

A closer look was taken of Barksdale AFB navigation aid sites. With more, detailed information a better picture emerges of the relationship of the sites to the main base. Barksdale AFB had a broad range of such sites: radio range, fan marker beacon, a TVOR, two separate middle marker sites, and an outer marker site.

Conclusions were that this data is of limited value on a broad scope, but that detailed research could be useful when studying the history of a particular base.


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