Assured of administrative stability under United Air Lines, personnel at LAES pressed forward in the development of the Integrated Landing System which they had been formulating during the previous months. Despite difficulties in procuring suitable materials, in obtaining access to privately owned land in the approach zone, and in securing the necessary technical personnel, construction of a working version of the Integrated System was accomplished with remarkable speed, in time for a revealing series of tests during the 1946 fog season.

The Bartow Type D_1 Runway Maker Light was installed along the instrument runway. This required the laying of 12,000 feet of conduit and the pouring of 72 concrete light bases. An entirely new type of approach lighting installation was constructed in the approach zone, requiring some 7,000 feet of conduit, the erecting of 36 steel towers varying in height from 7 to 84 feet, set on concrete bases, and the installation of a 600 kw portable generator and 36 individual transformers. (This is the Funnel Approach Light System devised by W. T. Harding of the Air Materiel command at Wright Field. A special Wide-Angle High Candlepower approach light was Constructed for AMC by the American Gas Accumulator Company, Elizabeth, N.J., and mounted on the towers at LALES.)

I addition to new lighting equipment, major alteration to the high pressure FIDO system were carried out during the summer of 1946, and the low pressure systems were restored to good condition after a winter's neglect. Similar neglect had rendered the ISL system inoperative. Portions of the equipment corroded by salt spray were replaced, and marker beacons were installed in the approach zone. Various expedients were devised to protect the equipment from weathering and to assure stability of the radio beams. To complete the electronic landing aids system, a GCA unit was obtained from Navy stock and technicians were located to operate and maintain it.

Despite the tremendous amount of new construction and repair work required, and the delays occasioned by material shortages, lack of personnel and equipment, and the difficulty of obtaining access to privately owned lands upon which some of the installations must be located, approximation of the Integrated landing system was achieved in time to conduct a series of test during the months of September and October of 1946. These 14 flight test series, in which over 100 landings were made during restricted visibility conditions, conclusively demonstrated the feasibility of making aircraft landing a routine procedure even in zero weather. Furthermore, it was shown that there is no reason why this system should not be put in use at once on commercial fields throughout the country.


The Integrated Landing System, proposed by the research staff of the Landing Aids Experiment station, consists of the following basic units:

(1) Electronic low approach aids which will assure that the plane is brought safely down the approach zone to the runway at an altitude suitable for landing.

(2) A suitable method of marking the approach and runway areas so that the pilot will be certain of his location and have adequate visual reference points for completing a contact landing.

(3) A fog dispersal system for extreme visibility conditions, which will nsure that the final approach and runway areas are visible to the pilot as he terminates his approach and sets his plane on the ground.

Figure l is an aerial view of LAES looking down the instrument runway.

The backbone of the Integrated Landing System is an electronic low approach aid. Tests at LAES have indicated that either the Instrument Landing System (SCS-51) employing radio beams, or the Ground Control Approach radar unit, can be successfully applied.

A. Instrument Landing System

The ground equipment of the ILS consists of two radio beam transmitters known as the Localizer and the Glidepath and three marker beacon transmitters. In addition, the aircraft must carry a special receiver tuned to the frequencies emitted by the ground transmitters.

The Localizer, Fig. 2, is installed beyond the terminal end of the instrument runway along the extended centerline. It consists of a directional antenna array mounted on an A-Frame, and a transmitter which may be housed advantageously in a vault underneath the antenna. The transmitter generates a carrier wave of 108.3 to 110.3 megacycles. A mechanical modulator generates frequencies of 90 and 150 cycles which are impressed upon the carrier wave. Bridge circuits and appropriate phrasing result in the propagation of a 90 cycle pattern on the left side of the runway and a 150 cycle pattern on the right (as viewed from the approach zone).Over the centerline, the overlapping of the two signals produces a narrow region within which the two signals are of equal strength. The airborne receiver measures the relative strength of the two signals and indicates the result to the pilot by deflecting a vertical needle to the left or right proportionally. Since the signal strengths vary directly with the distance of the plane from centerline, the amount of needle deflection shows an experienced pilot how much correction must be applied to bring the plan back to the centerline. For convenient interpretation, the circuit is arrange to deflect the needle.

The glidepath transmitter, fig. 3, located 1180 fet up the runway from the threshold, operates in a similar fashion, except that it generate a carrier wave of 332.6 to 335 megacycles. The narrow zone of equal signal strength slants upward from ground level at a small vertical angle which may be adjusted to clear any obstruction in the approach. (The normal angle is 2-3/4.) In the aircraft a horizontal needle is deflected up or down in proportion to the relative signal strengths, in a fashion similar to that employed for the Localizer needle.

The two needles are combined into one instrument, Fig. 4. when they cross at right angles, the aircraft is flying the true glidepath.

In addition to flying along the proper slanting line down the approach, it is important that the pilot landing in rain know the distance of his plane from the touchdown point. For this purpose, Marker beacon transmitter, fig. 5, are located along the approachway centerline at selected distance from the runway threshold. These transmitters operate at 75 megacycles and project a coded signal vertically. On the aircraft panel a flashing light indicates that the plane is passing over the maker beacon.

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GCA consists of two separate radar devices. The first, a search radar unit, having a 360 deg. scan, locates all planes flying within 30 miles of the field. Using this set, a controller can pick up a plane at a distance and give him appropriate course instructions to bring him into the approach zone at the proper altitude and heading. In addition, this unit is used for air traffic control, allowing a number of planes to be flown safely in the same general area while lining up for successive landing.

When the plane enters the approach zone, it is followed on a second set of highly accurate radar scopes, Fig. 7, which can scan an angular region over the approach 20 deg. wide and 7 deg. high. These scopes show the relationship of a plane to the field in azimuth, altitude, and longitudinal distance. As the "pip" representing the plane travels across these accurate scopes, operators track its progress with "cursors", whose setting are relayed to a pair of indicators located at the controller's desk. These indicators continuously show the location of the plane relative to the pre-select glidepath in terms of feet of deviation above or below, and to left or right, of the ideal path. An accuracy of ten feet can be obtain in measuring deviation with present GCA equipment. The Controller reports these deviation to the pilot, giving him corrections as he comes in.

Both the ILS and the GCA instruments have been used in low visibility landing at LAES. Both have proven dependable for usby well-trained pilots. At the present time, a controversy is growing up over the relative merits of the two devices. Pilots and technicians at LAES who have had the opportunity to use both systems, feel that the real question to be solved is not "which" should be used, but rather how to obtain immediate installation of "both and __" at airports throughout the nation. Information coming from government and private research laboratories on NAVAR, TELERAN , and LORAN indicates that radar, and television networks will, in the foreseeable future, link all aircraft with airways control centers. In the meantime, the air traffic control features of GCA are indispensable to the successful control of present air traffic over "socked in" airfields, while ILS provides the most economical and speedy means now available for guiding en aircraft to an invisible runway.

C. High Intensity, Wide Angle Approach Lighting

As a plane approaches the runway on an electronic approach, it becomes important that the pilot be provided with adequate visual reference points from which he can determine his location, altitude, attitude, and speed, relative to the runway upon which he is to land. Although electronic aids will bring the plane safely to the runway at an elevation as low as 50 feet, the visual references should begin considerable distance out in the approach zone, in order that the pilot will have ample time to locate himself and ready his plane for the touchdown. They must also be visible and identifiable with certainty from points above the level of the ideal glide path, since many pilots will be unwilling to reduce altitude before seeing what lies below. In addition, since deviations will occur to the left and right of centerline, the approach lights must be visible and identifiable from points to left and right of the true glide path.

The length of an approach lighting installation depends primarily on the landing speed of the aircraft using it, and on the time deemed necessary for the pilot to readjust from instrument flying to contact flying. Current approach light design calls for an installation extending from runway threshold to a point 3000 feet out in the approach zone. A median figure for landing speed a plane will traverse a 3000-foot approach zone in 17 seconds; flight tests indicate that such an installation provides adequate time for the final adjustments landing.

A study of deviations from true glidepath was made by the Army Air Forces Equipment Laboratory at Newark. The analyses of numerous approaches on electronic aids showed that at the Middle Marker, (3500 feet from threshold), all pilots should pass through a rectangular portal extending from 100 to 500 feet above runway level and spreading 350 feet to either side of the approach centerline. Accordingly , a funnel

shaped approach light pattern, Fig. g, was designed, in which two rows of lights are placed symmetrically with the approach centerline. At the approach end, the light rows are 700 feet apart. Moving toward the runway, successive lights are placed closer to the approachway centerline. At a point 700 feet from the converging light rows change direction and run parallel with the runway for the remaining distance. This pattern channels the landing at a safe altitude before coming over the runway.

Several problems had to be solved in designing a light suitable for the funnel installation. In order to establish the ground plane, it is important that the pilot see at least 3 of the lights in one row at all time during his transit though the approach funnel. The lights, therefore, must produce a beam of extremely high candlepower which will penetrate the intervening fog. In order to be visible from any point within the rectangular portal described about, they must have a wide horizontal and vertical distribution. In addition, the light source must be small in cross section, so that it will function effectively as a point source and thus have approximately the same apparent candlepower when viewed by the eye as when measured by photometric methods. Finally, the lights must be so located and aimed as not to be obscured by the aircraft structure.

The candlepower required to penetrate a dense daylight fog (daylight object visibility 165 feet, or 1/32 mile), as calculated from the empirical formula of Allard and Koschmieder1, becomes astronomical at a distance of 990 feet. It is, however, practicable to build a light source for the penetration of moderate fog (daylight object visibility 660 feet or 1\8 mile) for a distance of approximately 1000 feet. For this penetration, in daylight fog, 24,000 candlepower is required. (At night, it should be noted, 60 candlepower will penetrate the same distance because of the greatly reduced background brightness.) It can readily be seen that a 24,000 candlepower light will b more than adequate to cover the area between converting light rows, whose maximum separation is 700 feet, up to an elevation of 500 feet above the lights. In the left half of the approach funnel, the pilot will pick up at least three lights on his side; in the right half, the co-pilot will see the corresponding right hand row. And as the plane advances into the funnel along a slanting glide path, both rows will come into view ahead of and alongside the aircraft, outlining the correct path to the runway. Spacing of the lights is, of course, important. At the approach end of the funnel, the lights are located 100 feet apart, as measured along the funnel centerline, for the first 600 feet. This spacing gives thoroughcoverage of the funnel at the critical point where the pilot first makes contact. The spacing over the remaining 2400 feet of the funnel is 200 feet, since in this region, the decreased aircraft elevation, and the convergence of the rows will give full coverage.

Within the funnel system, cockpit visibility restrictions become a problem only when the pilot flies high and almost over a row. In this position, the cockpit structure will obscure the lights below the plane while the opposite row may be attenuated below the pilot's visual threshold. Good instrument pilots, however, do not deviate to this extent in both azimuth and altitude from the indicated electronic glidepath.

Figure 9 shows the light used in the funnel system. A wide angle beam emanating from a small source was achieved by locating the monoplane filament of a spherical reflector having a 10 - inch radius and subtending 120 degrees horizontally by 80 degrees vertically. In front of the light source is a vertical condenser of clear glass, so ground as to produce a beam 35 degrees wide in the vertical plane. In front of this is a horizontal condenser accurately moulded of aviation red lucite, composed of vertical prisms which concentrate the light into a uniform beam 45 degrees wide. Isocandle curves for the completed unit show that it has a peak output of 25,000 candlepower, and not less than 15,000 candlepower over a rectangular beam 45 degrees wide and 35 degrees high.

The American Gas Accumulator Company of Elizabeth, New Jersey, designed the optical system for the High Intensity Approach Light and manufactured the units under test at the Landing Aids Experiment Station.

The AGA lights are aimed so that the outer edge of the rectangular beam is projected along the light row. In addition, the outer lights are tilted upward to cover the higher elevation of the glidepath at the approach end of the

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