Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.


  1. Advanced Patent Search
Publication numberUS2475256 A
Publication typeGrant
Publication dateJul 5, 1949
Filing dateMay 15, 1942
Priority dateMay 15, 1942
Publication numberUS 2475256 A, US 2475256A, US-A-2475256, US2475256 A, US2475256A
InventorsSamuel P Saint
Original AssigneeGen Railway Signal Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Airplane traffic controlling system
US 2475256 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

July 5, 1949. S. P. SAINT 2,475,256

AIRPLANE TRAFFIC CONTROLLING SYSTEM Filed May 15, 1942 3 Sheets-Sheet l Q m. u. m g m x3 T ,JKEM 1 July 5, 1949. s. P. SAINT 2,475,256

AIRPLANE TRAFFIC CONTROLLING SYSTEM Filed May 15, 1942 s Sheds-Sheet 2 FBG.3. FIG. 4.

ATTORNEY Jun) 5, 1949. s, sA|NT 2,475,256

AIRPLANE TRAFFIC CONTROLLING SYSTEM Filed May 15, 1942 3 Sheets-Sheet 3 n: new 010 F 1&5.

'INVENTOR ATTORNEY Patented July 5, 1949 AIRPLANE TRAFFIC CONTROLLING SYSTEM Samuel P. Saint, Port Washington, N. Y., assignor to General Railway Signal Company, Rochester,

Application May 15, 1942, Serial No. 443,116

6 Claims. 1

This invention relates in general to airplane traflic controlling systems, and has more particular reference to a system for controlling the flight of planes between, and the approach of planes to, airports, and the safe landing of planes at airports.

Airports may be located in such country that approaching planes encounter various hazards before reaching them. The hazards may be tall buildings, towers, hills or the like, and unless some safe signalling system be employed for guiding the planes, they must fly, in the interest of safety, more than sufficiently high to clear the obstructions. In many cases, particularly under conditions of poor visibility, the planes must approach at such high levels that landing is difficult and may require several attempts before being effected.

Furthermore, after a plane has reached an airport, there is possibility of confustion in identifying the runway to be employed, which runways are generally outlined by marking lights.

It is proposed, in accordance with this invention, to employ a rotating light signal displaying a pluralit of colored light beams, so as to furnish a guide for any plane approaching the airport or other location. The rotating light is also to be raised and lowered, in accordance with the hazards surrounding approach to the airport, or other location, so as to properly define a path clearing such hazards.

It is also proposed, in accordance with this invention, to designate the runways or air routes by a plurality of light signals, each of which displays a beam having a plurality of colored portions so as to distinctively designate the runway, and, furthermore, to form an easily identified glide path for guiding a descending plane to safely land at the proper point on the runway.

Further objects, purposes, and characteristic features of this invention will appear as the description progresses, reference being made to the accompanying drawings, showing, solely by way of example, and in no manner whatsoever in a limiting sense, a plurality of forms which the invention can assume. In the drawings:

Fig. 1 is a diagrammatic, plan view of an airport and its surroundings.

Fig. 2 is a diagrammatic, elevational view of the airport of Fig. 1.

Fig. 3 is a fragmentary, diagrammatic, sectional view, with parts shown in elevation, of a rotating signal such as employed in this invention.

Fig. 4 is a sectional view, on an enlarged scale, of the rotating signal of Fig. 3.

Fig. 5 is a diagrammatic, elevational view of runway signal means, to an enlarged scale, in accordance with this invention.

Fig. 6 is a diagrammatic fragmentary sectional view of a runway signal and associated runway.

Fig. 7 is a circuit diagram in accordance with this invention.

Fig. 8 is a diagrammatic plan view of a modified form of runway signal and the associated runway.

Fig. 9 is a sectional elevation with parts in elevation, on line 9-9 of Fig. 8, viewed in the direction of the arrows.

Referring now to the drawings, and first to Fig. 1, there is here shown, in a wholly diagrammatic fashion, an airport I, having a plurality of differently directed landing runways 2, 3, 4, 5, 6, l, 8 and 9. Suitably located on the landing field, and preferably more or less centrally, is a light signal S, mounted on a mast ii, if desired.

The runways 2, 3, etc. will be employed in the usual way for planes to land when traveling into the wind, and, thus, one or another of them will be used at any particular time, in accordance with weather conditions. Each runway has embedded in it, and preferably longitudinally centrally thereof, two signal lamps, such as lamps l2 and 13 for runway 5, and constructed and directed as described below. Merel by way of example, there has been shown at the left of the landing field an obstruction in the form of a tree l4, while at the right is a relatively distant obstruction in the form of rising ground forming a hill 15, and a nearer obstruction in the form of tree I5 A port building I0 is also located to the left of the landing field.

It is clear that if no signalling system be employed, an approaching plane, under conditions of low visibility, in the interest of safety will generally approach the field from an elevation higher than is really necessary, and, hence, to land, it may be necessary to make several attempts, whereas with a proper signalling system, the hazard can be safely avoided, by just a safe margin, and landing can be very greatly facilitated.

The rotating signal S is shown in greater detail in Figs. 3 and 4. This signal is constituted by a base B, which, through legs 18, supports a motor M, of any desired constant speed type, such as a synchronous motor. This motor, through gears 96 and I6, drives a vertically positioned shaft ll, passing loosely through a cam C, which is supported on, and fixed to a housing I8 carried on legs I 8. The shaft I! has pivoted to it as at I8 an offset arm 19, which carries the signal S.

Lead-in wires 20 are connected, as shown, to supply the motor and the signal with energy, which can be either alternating or direct, depend-- ing upon the type of motor, and signal employed. Signal S is supported by an arm 2!, carrying a roller 22, which rolls on the cam surface 23, of cam C, as the signal is rotated by the motor.

Cam C is formed, as shown, to conform with the topography ofthe country immediately surrounding the airport. For example, the cam has a relatively high portion 24, positioned to tilt the signal S more steeply upwardly, when in its rotation it is directed toward hill [5, and another relatively high portion 25, positioned to tilt the signal more steeply upwardly, when it is directed toward tree M. In this manner, the various hazards surrounding the airport, and constituting danger points for an approaching plane, can be translated into hills and valleys on cam C, so that signal S, in its rotation, will rise and fall and maintain a predetermined elevation above the various approach obstacles.

As shown in Fig. 4, the signal is constituted by a casing 26, and a light source 21, positioned at the focus of a parabolic reflector 28 whereby light rays are directed forwardly out of the signal in a parallel beam by the reflector. Closing the front end of casing 26, is a lens L, formed with a smooth convex outer surface 29, and a horizontally positioned fluted prismatic surfaced inner face. These curved prismatic faces 3!], are so arranged that the emerging beam of parallel rays is spread upwardly from the optical axis 3!, for the upper half of the beam, and downwardly from the optical axis for the lower half of the beam, it being noted that the faces 30 controlling the upper half of the beam are reversely positioned with respect to the corresponding faces 32 controlling the lower half of the beam.

The lens L is made of colored transparent material such as glass with the upper half colored green, G, and the lower half colored red, R. Thus, the light emitted from signal S is composed of a beam which spreads upwardly and downwardly in a vertical plane and is colored green from the optical axis upwardly, and red from the optical axis downwardly. Also the beam is spread horizontally through a suitable angle by the lens outer curved face. Accordingly, as the signal S is rotated, it forms a cone of light for signalling to approaching planes, and the elevation of the beam is so arranged as to maintain the lower border of the green zone, G, a safe minimum distance 33 above the various hazards encountered by a plane as it approaches the airport.

Furthermore, the signal constitutes a beacon of the flashing type, and is rotated at a frequency distinctive of the particular airport with which it is associated, as, for example, fifteen revolutions per minute. Thus, the beacon identifies the airport and constitutes a light path of a distinctive color, so that an approaching plane need merely pass through the lower red zone, R, until it enters the green zone, G. At this point the pilot knows that he is suificiently high enough to avoid various obstacles and need merely glide downwardly toward the airport within the green zone, and preferably along the lower border .of the green, where it verges on the red and becomes a distinctive grayish color.

Upon reaching the landing field, the pilot will receive instructions as to what lane he should use for landing his plane, and the present invention provides means for facilitating identification of this runway and landing of the plane on the designated runway.

As referred to above, each runway, such as the one 5, shown in Fig. 5, has a plurality of signals as l2 and i3 spaced from each other and positioned preferably along the longitudinal center line of the runway and directed outwardly toward an approaching plane. Each of these signals can be constructed, in general, as described in connection with signal S so far as regards its optical characteristics. These runway signals, however, are stationary instead of being rotatable as is the signal S, and hence, involve no motor or cam and associated parts. The runway signals include parabolic reflectors, with suitable light sources and a two-colored lens colored green and red, as described in connection with signal S.

For facilitating identification of the landing runway to be employed at any one time, apparatus is provided for intermittently energizing the signals for but one runway at any one time, whereby to provide signals of characteristic colors flashing at distinctive rates.

In Fig. 7 is shown one circuit arrangement for controlling the runway lights. The lights for each direction on each runway are connected in multiple to individual energizing wires. For example, signals 52 and [3, which are positioned in runway 5 for east bound planes are energized through a line Wire 40, while the other pairs of lights only some of which are shown, are energized through other individual line wires, as 4|, 42 and 43. Each energizing wire, as 40, is connected to an individual backcontact, as 44, and the various back contacts .are conveniently arranged in an are so as to be passed over successively by afront contact 46, which is normally spaced above the back contact, and is operated by a rotatable and depressible control switch SW. Thus, the control switch can be rotated to be positioned above the back contact which it is desired to select and then can be depressed against the friction of a catch 69 to be retained in depressed position until moved therefrom by the catch 60 cooperating with a groove 6| in the switch.

The front contact 46 constitutes a part of a switch arm, which includes a contact 41 separated from contact 46 by insulation or the like 62, and having a flexible finger 63 for making contact both before and after the depressing of the switch, with a motor control sector 64, as shown. It can be noted that sector 64 makes contact with fingers '63 before front contact 46 has reached a position above the first back contact 44 for the light control.

The light control front contact 46 is connected by means of Wire 56 to one contact 48 or an interrupter contact arrangement having a cooperating contact '49 which is normally spaced from contact 48, but which is closed on contact 48 when operated by any one of the rises 56 on a coding wheel ill. The coding wheel 5| is connected to an operatin motor 52, which-can be of any desired type of constant speed motor, such as a synchronous motor or a constant speed direct current motor.

As shown in Fig. 5, the inner signal l2, has an outer lens which is red and green with the red positioned above the green, while the outer signal l3 has a lens colored red and green, but in this case the lens is rotated 180 so that the upper portion is the green, and the lower portion is the red. As shown, the signals are so arranged that the beams from the two signals overlap to constitute diiferent distinct color zones for a plane traveling horizontally above the air field and cutting through the beams and are tilted at an les to constitute a suitable glide path and to clear obstructions, if any, such as tree m by a safe margin, 33.

The path of an approaching plane, as 35, of Fig. 2, is continued after the plane reaches the landing field along a path which can be diagrammatically represented as 36 of Fig. 5. It can be seen that to continue to travel along a horizontal line, such as 31, a plane approaching the airport first encounters a red zone, B, or, in other words, the pilot sees a single red light. As he continues along this line 31 he encounters a G/G zone and sees a green light over a green light. Next, he encounters a red light over a green light, or an R/G zone, and further progress brings him an R zone, where he sees a single red light.

The signals 12 and i3 constituting the signal means for a particular runway are so arranged that the zone G/G forms a descending glide path, so far as possible, of the ideal angle for proper landing of the plane, while the first R zone encountered, as described above, extends to the ground to leave no open danger zone near the ground.

Accordingly, upon circling the field, the pilot need merely sight a single red light upon which he can approach horizontally toward the airport, and after entering the R zone, he knows that he must continue horizontally and not lose elevation, since he knows that he is below the glide path zone (3/ G. Upon continuing, he enters the glide path zone and then need merely follow this zone to land certainly and safely and at a suitable point and without danger of overshooting his mark and requiring a further circling of the field and further attempts to land.

As the pilot glides to a landing in the glide zone G/G, should he glide too steeply, he will encounter the zone B and will know that he must decrease his angle. he glide less steeply than proper, he encounters the zone R/G, or R, according to his then elevation, which apprises him of the fact that he must increase his angle. The two limiting red zones, R, are so widely spaced from each other that there need be no confusion in the mind of the pilot as to whether he is above or below the glide zone path (3/ G.

Furthermore, should it be desired, these limiting zones, described as red, can be of different colors. To effect this, it is merely necessary, for example, that the signal l2 should have a lens showing yellow over green, that is Y/ G, and the signal it a lens showing green over red, that is G/R. With this arrangement, at certain elevatlons the glide path is green over green, G/ G, with the zones beyond this path yellow over green and yellow, i. e. Y/G and Y, and the zones before this path green over red and red, i. e. G/R and R. Other colors could be employed if desired, such as a signal l2 showing R/ G, and a signal l3 showing G/Y.

Signals S, [2 and i3, etc. have been represented wholly diagrammatically without showing details of construction and adjustment, etc., since it appears unnecessary, for the purpose of the disclosure, to enter into these refinements. It is to be understood, however, that a suitable, commercially acceptable signal will be employed, and the construction of the same can follow the lines of On the other hand, should 6 the signal as disclosed, for example, in the patent to Moore, No. 2,239,336, granted April 22, 1941.

With the system of airplane tralhc control as described above, it is clear that the approach of a plane to an airport, under conditions of low visibility, and the landing of the plane at the port, has been greatly facilitated and safeguarded, and particularly so in the case that the country surrounding the port is of a character to present either natural or man-made hazards. These hazards can be safely avoided by the pilot, by sight, under conditions of good visibility, but when visibility is poor, the present system furnishes means for handling planes with a safety and facility which is substantially equal to what can be accomplished under good visibility conditions.

In Figs. 8 and 9 is shown a modified form of the invention, wherein additional landing lights are employed. Merely by way of example, there is shown a landing runway i2 having lights I2 and 3 spaced lengthwise of the runway, as described above. In addition to these two lights there are employed two other lights Hi and ii spaced crosswise of the runway. These lights are of the same type of runway lights as described above, and are controlled in the same manner. That is, in the case of the form shown in Fig. 8, the four lights I2 I3 Ill and H constitute a group separate from other light groups for other runways, and are to be controlled in the same manner as described above in connection with Fig. 7 for the groups of landing runway lights each of which group includes but two lights.

The lights I2 and I3 emit beams as described above of the colors red and green and arranged as shown in Fig. 5.

The lights 19 and ill have a vertical division line between the two different colored beams emitted from each light, and the beams are red and green as shown in Fig. 8 and overlap as shown, with the two green beams to the inner side.

With this arrangement, it can be seen, a glide path is defined not only by limiting zones above and below it, but by limiting zones to the right and to the left of it. Thus, the glide path which constitutes not only a green light over a green light, but also a green light to one side of another green light, forms a sort of tunnel, defined on four sides by differently colored zones. The green zone from the two longitudinally spaced lights approximately coinciding with the green zone delined by the transversely spaced lights.

As seen in Fig. 9, to the left of this green glide path is a red light to the left of a green light, while beyond this is a red light, and to the right of the glide path is a red light to the right of a green light with a red light beyond this. This type of glide path which is defined on four sides is more accurately defined and diiferently defined. than the one described in connection with Fig. 5, which latter is defined merely in a vertical plane, and in many cases this second form has advantageous uses over the simpler form.

The various landing lights described above have been described in connection, generally, with an airport, but it is obvious that all of them can be used in other connections, if desired, without departing from the scope of this invention. It is possible a situation might arise where several obstructions surrounded a flat open space which constituted a portion of a much traveled route, and in such case, a rotating beacon of the form shown in Fig. 2 could be used to advantage, al though this open space need not be a landing field at all.

;In regard to the runway lights, it is entirely possible that it might be desirable to use them in defining sections of routes which are limited both horizontally and vertically, as, for example, in following a route between steep hills on each side thereof, or following a canyon. In such case it is desirable, not only to maintain the plane at a safe altitude, but also to .maintain the plane "within safe limits in a horizontal direction. Also, it is possible that routes might be connected by .cross routes passing through mountain passes or deep narrow valleys, defined by steep hills at each side, and in such case, guiding lights such as described in connection with landing runways of the form both of Fig. and Fig. 8, might be used to advantage, and such use is contemplated by this disclosure.

.It should be noted that the combination of a rotating beacon having a multi-colored light beam for indicating the safe approach from all directions to an airport having variable height obstructions has been disclosed and claimed in .the divisional application Ser. No. 792,811 filed December 19, 1947; and no claim is intended to :be made herein to such subject matter.

The above rather specific description of the several forms which the present invention can assume, has been given solely by way of example and is not intended, in any manner whatsoever, in a limiting sense. It is intended that all such variations, modifications, and adaptations, as may, from time to time appear desirable, be incorporated in the present invention without departing from the scope and spirit of this invention, except insofar as it may be limited by the appended claims.

Having described my invention, I new claim:

1. In airplane control systems, for use on landing .field runways, visual signal means including .two light signals, positioned in line in the runway and spaced from each other and positioned vto-face outwardly of the runway, each signal in- .cluding means for emitting an upper part beam of one color, and a lower part beam of a difierent color, the upper part beam of the outer signal being of the same color as the lower part beam of the inner signal, and mounting means for directing said signals so that their beams overlap on an upwardly inclined path, so that the zone common to said lower and upper part beams defines a suitably inclined safe glide path for a plane landing on the runway. 1 ,2. In airplane-control systems, for use on landing field runways, visual signal means for each runway including two light signals directed outwardly of the field, positioned in line in the runway and spaced from each other, each signal havingfmeans causing it to emit a beam of one color and spreading upwardly from the optical axis of the signal and a beam of a difierent color and spreading downwardly from the optical axis of the signal, the outer signal having its upper beam of the same color as is the lower beam of the inner signal, and means for supporting the two signals in such positions as to cause their beams-to overlap in an upwardly inclined :path with their optical axes substantially parallel whereby to define a colored landing glide path by the zone common to the same colored beams of the two signals.

3. In airplane control systems, for use on landing field runways, visual signal means including two light signals facing outwardly of and positioned in line in the runway, and spaced from each other, each signal having means causing it to emit a beam of one color and spreading upwardly from the optical axis, and a beam of a different color and spreading downwardly from the optical axis, the outer signal having its upper beam of the same color as the lower beam of the inner signal, means for supporting the two signals in such positions as to cause the upper .beam of the outer signal to overlap both beams of the other signal and to cause the lower beam of the other signal to overlap both beams of the outer signal with the optical axe of said signals being substantially parallel to each other by extending in an upwardly inclined direction whereby'to define a landing glide path by the zone com- .mon to the same colored beams from the two signals, and an upper warning zone and a lower warning zone, respectively above and below said glide path, the upper zone appearing to an approaching plane as said one color over said other, and the lower zone, appearing as said other color over said one color.

4. In a system for landing planes at an airport having at least one runway, a first light signal unit located on said runway and being capable of projecting a light beam of one distinctive color above its beam axis and. a different distinctive color below its beam axis, means for mounting said first light signal to project its beam along said runway at an angle from the horizontal suitable for landing a plane, and a second light signal unit located on the runway spaced outwardly from said first unit and being capable of projecting a light beam of said different distinctive color above its beam axis and a said one distinctive color below its beam axis, means for mounting said second light signal to project its beam along said runway towards said first unit at the same angle from the horizontal as said first unit, whereby the upper portion of the beam of said first unit and the lower portion of the beam of said second unit overlap to provide a continuous glide path indication of correspondin color and having substantially parallel boundaries withdistintive indications above and below such glide path to aid a plane in following the path to said runway.

5. In a system for directing airplanes in landing on an airfield runway, two pair of light projecting units directin their light beams along the runway in the direction from which an airplane is to land, each of said units causing its light beam to be differently colored on opposite sides of a beam axis, means mounting one pair of said units so that their correspondingly colored beam portions overlap and their beam axes form boundaries on opposite sides of said runway, and other means mounting the other pair of said units so that their correspondingly colored beam portions overlap and their beam axes form the upper and lower boundaries of a safe landing course inclined downwardly toward said runway, whereby an airplane may safely land by following a light beam of a particular color and will be given a distinctive indication of a difierent colored light beam if it leaves the defined safe course.

6. In a system for directing airplanes for landing on an airfield runway, two laterally spaced light projectin units, one on each side of the runway, and each including means for projecting a light beam of one color on one side of its beam axis and a different distinctive color on the other side of its beam axis, means for mounting said units so that their beam axes are substantially parallel to said runway and in such relationship as to cause their two beams to overlap with respect to correspondingly colored portions to thereby give a distinctive indication along the runway as compared to the indication to either side of the runway, two other light projecting units longitudinally spaced along the runway and each including means for projecting a light beam of said one color on one side of its beam axis and said different color on the other side of its beam axis, and means for mounting said two other light projecting units so that their beam axes are substantially parallel to each other and in such relationship as to cause their two beams to overlap with respect to correspondingly colored portions and with their beam axes extending with a rising angle with respect to the level of said runway but with their beam axis planes at right angles to the beam axis planes of said two laterally spaced units, whereby an airplane can safely descend to said runway by following said distinctive indications as provided by said longitudinally spaced light projecting units determining the upper and lower boundaries of a safe landing course with said laterally spaced light projecting units giving a diflerent indication if the air- 5 plane deviates to either side of said safe landing course.


10 REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,235,065 Schweizer July 31, 1917 1,239,155 Brockelbank Sept. 4, 1917 1,342,860 Mortimer et al June 8, 1920 1,343,899 Best June 22, 1920 1,774,842 Peters Sept. 2, 1930 1,869,922 Soucek Aug. 2, 1932 1,948,552 Weber et a1 Feb. 27, 1934 1,989,095 Howard Jan. 29, 1935 1,989,295 Sewell Jan. 29, 1935 2,023,708 Spring Dec. 10, 1935 2,155,295 Bartow Apr. 18, 1939 2,212,537 Coulter Aug. 2'7, 1940 2,386,268 Roper Oct. 9, 1945' FOREIGN PATENTS Number Country Date 125,460 Great Britain Apr. 24, 1919 402,632 Great Britain 1933

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1235065 *Jan 25, 1917Jul 31, 1917Gottfried E SchweizerHead-lamp for automobiles.
US1239155 *Feb 12, 1917Sep 4, 1917Clarence Hartree BrockelbankApparatus or device to control safe night landing of aeroplanes.
US1342860 *May 13, 1919Jun 8, 1920Frederick PottenApparatus for facilitating the landing of aircraft
US1343899 *Sep 9, 1916Jun 22, 1920 Signal-lamp
US1774842 *Jul 7, 1928Sep 2, 1930Thomas K PetersBeacon light
US1869922 *Sep 15, 1930Aug 2, 1932George SoucekLuminous signaling device
US1948552 *May 16, 1932Feb 27, 1934Jensen Edward WRay aviation compass
US1989095 *Oct 16, 1929Jan 29, 1935Howard Dudley BWind direction indicating airways beacon
US1989295 *Jul 27, 1929Jan 29, 1935Sewell Arthur TLanding signal
US2023708 *Oct 6, 1933Dec 10, 1935Spring Henry IElevation beacon for aircraft and the like
US2155295 *Mar 21, 1935Apr 18, 1939Bartow Beacons IncAirport lighting system
US2212537 *Jan 15, 1936Aug 27, 1940Coulter Fred DAircraft landing-floor beacon
US2386268 *Jan 18, 1938Oct 9, 1945Roper John MApproach light
GB125460A * Title not available
GB402632A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2570138 *Aug 22, 1947Oct 2, 1951Wallace & Tiernan IncSingle station range light apparatus
US2597321 *Apr 5, 1949May 20, 1952Rudolf C HergenrotherAircraft approach system
US2968023 *Aug 21, 1956Jan 10, 1961Gen Electric Co LtdVisual position-indicating arrangements
US2990469 *Mar 3, 1959Jun 27, 1961Barbier EtsLighting device embedded in the ground, in particular for airfields
US3353153 *Jan 22, 1965Nov 14, 1967Alan W BaldwinOptical guidance system for providing vehicle motion error information
US4015235 *Jun 6, 1975Mar 29, 1977The Rank Organisation LimitedAircraft parking guidance indicator
US4532512 *Nov 22, 1982Jul 30, 1985Tanner Jesse HOmnidirectional approach slope indicator system
DE1213747B *Sep 27, 1960Mar 31, 1966EdgertonOptisches Landesystem
EP0324628A2 *Jan 12, 1989Jul 19, 1989Leech (Rochester) LimitedPath guidance indicator apparatus for vehicles or craft
U.S. Classification340/955, 362/233, 362/231, 340/950
International ClassificationG08G5/02, G01S19/41, G01S19/15, G01S19/07, G01S1/02
Cooperative ClassificationG08G5/0026, G08G5/025, G01S1/02, G08G5/0043
European ClassificationG01S1/02, G08G5/02E, G08G5/00D, G08G5/00B4