Patent Description:
A precision approach path indicator (PAPI) is a key part of airfield ground lightning system used at airports. It provides guidance information to help a pilot acquire and maintain the correct approach and land the airplane safely. PAPI warns pilot about too high or too low approach in relation to the ground. Typically a PAPI system comprises four units that are positioned in a row at the side of the runway. The units are equally spaced and each unit transmits a colour-coded light output, typically white and red. The colour-coded light output provides a visual indication of an aircraft's approach position relative to the designated glide slope for the runway heading. When an aircraft approaches the runway, the angle of its approach determines whether the light beams appear red or white to the pilot. If the aircraft is approaching on the correct glide path, the four light PAPI system will show two red lights and two white lights. If the position of the aircraft is too high, the number of white lights increases. If the position of the aircraft is too low, the number of red lights increases. The guidance of the lights makes it easy for the pilot to adjust the position of the aircraft and land in the designated part of the runway.

An important aspect of PAPI systems is separation of the white light from the red light, so that they do not overlap each other. Traditionally, the separation is made by wall/divider which prevents transmission of light from the red sector to the white sector and vice versa. In order to effectively block unwanted transmission of the red light or white light, the divider may be covered with layer selective with regard to the transmission of the red/white light. Alternatively divider can be made with very sharp edge.

Publication <CIT> discloses an optical system comprising a red light LED and a white light LED as light sources, and characterized by comprising a set of lens-containing red LED and white LED, an array of light source modules and a set of lenses in two halves and a spacer sandwiched between two halved lenses and a set of prism assemblies. The lens assembly forms an optical system in which the red light is above and the white light is down after the array of red LEDs and white LEDs passes through the lens. The prism assembly is divided into an upper prism assembly and a lower prism assembly. The center line of the light exit surface of the prism assembly is close to the focal plane of the lens assembly.

In <CIT> there is provided a Precision Approach Path Indicator (PAPI) unit, said unit comprising first and second light sources and a projection lens assembly, wherein light emitted by the first and second light sources is collected by first and second solid waveguides respectively and is guided by said waveguides to an intermediate plane, said intermediate plane being located in the focal plane of the projection lens assembly.

Publication <CIT> discloses an apparatus, comprising: a first mounting surface for mounting an array of light emitting diodes, the array of light emitting diodes comprising a first set of light emitting diodes emitting a first color and a second set of light emitting diodes emitting a second color; a second mounting surface having a pair of apertures optically coupled with the array of light emitting diodes, the pair of apertures are separated by a precision ground blade, wherein the precision ground blade has a first edge and a second edge, the first edge is closest to the array of light emitting diodes and the second edge is opposite the first edge, the first and second edges having different thicknesses; a third mounting surface having a first lens mounted thereon, the first lens optically coupled with the array of light emitting diodes and receiving light from the array of light emitting diodes; and a front surface having a second lens mounted thereon, the second lens optically coupled with the first lens and receiving light from the first lens.

In <CIT> there is provided a LED based precision approach path indication (PAPI) system for guiding a landing aircraft to a pre-determined approach path comprising of multiple light housing assemblies (LHAs), each of the LHAs comprising of one or more lighting assembly modules, wherein each of the lighting assembly modules comprises: an array of white LEDs; an array of red LEDs positioned above said array of white LEDs; a plurality of collimating lens, each being placed in front of each LED of said array of white LEDs and said array of red LEDs; an optical combiner being placed in front of said array of red LEDs and being slightly above a first plane where said array of white LEDs are placed; and a projection lens set which is positioned in front of said optical combiner; wherein said optical combiner is a six face lens comprising an input refractive surface facing said LEDs, an output projection surface facing said projection lens set, a flat top surface, and a flat bottom surface having a reflective coating to block white light and increase white light intensity near transition zone, said output projection surface having a filter coating which is transparent with red light.

In <CIT> there is provided a generating device for generating a light beam with three or more sectors for a glide angle indicator for aircraft, comprising: illumination means including at least a first LED source, a second LED source and a third LED source; a projection lens aligned with the illumination means along a direction of propagation of a light beam; an optical guide unit interposed between the illumination means and the projection lens, facing the first, second and third LED sources and extending away from the first second and third LED sources along the direction of propagation, for generating an image comprising at least three different sectors of the light beam; wherein the optical guide unit comprises at least a first guide at least partly defined by a gaseous volume and a second guide defined by a solid body, both the first guide and the second guide facing a respective one of the first, second and third LED sources permeable to the light and extending away from the respective one of the first, second and third LED sources along the direction of propagation, at least one chosen from the following arrangements: wherein the optical guide unit comprises two second guides, each defined by a solid body, wherein the first guide is interposed between the two second guides; and wherein the optical guide unit comprises two first guides, each at least partly defined by a gaseous volume, wherein the second guide is interposed between the two first guides.

The object of the invention is a lamp for a precision approach path indicator as in claims from <NUM> to <NUM>. The advantage of the claimed lamp is ease of production, maintenance and service. In addition, using an offsetting element, the cost of production and installation and setting up of the PAPI systems might be significantly reduced.

The accompanying drawings incorporated herein and forming a part of the specification illustrate the example embodiments.

<FIG> shows a general principle of the operation of a PAPI system on the basis of a pilot's eye view of such a system. A PAPI system comprising a row of four lighting units installed alongside of the runway, each unit can consist of one or more lamps close by. Each of the four lighting units emits a beam of light consisting of white light in the upper part and red light in the lower part, so each beam is split horizontally. Two of the light sources are arranged to transmit at angles slightly greater than the optimal approach angle of the aircraft, and the other two at angles that are slightly smaller than the optimal approach angle. The result is that a pilot approaching the runway on the correct path sees two red lights and two white lights. When the path the aircraft in relation to the runway is too low, the pilot sees more red lights for example three or four. When the path of the aircraft is too high, the pilot sees three or four white lights.

An optimally working PAPI system should be set up precisely and maintain a clear and sharp color change boundary, this transition zone should be as small as possible in order to give the pilot clear information about the glide path of the aircraft.

<FIG> shows a schematic cross section of a lamp according to the invention in the preferred embodiment. In this embodiment the lamp for a precision approach path indicator comprises a number of light sources <NUM>, <NUM>, <NUM>, <NUM> emitting an electromagnetic radiation of a different wavelengths, for example white light, red light and infrared radiation. In one of the embodiments of the invention the lamp can be further provided with at least one, and preferably two additional radiation sources of a third wavelength.

The radiation from radiation sources <NUM>, <NUM>, <NUM>, <NUM> is collimated with the optical elements <NUM> such as lenses or mirrors in such a way that the desired illumination is achieved in the intermediate plane <NUM>. The desired illumination means the illumination pattern appropriate to use as a PAPI landing lights as described in relation to <FIG>. For the first beam of light or radiation in the upper section with the sources <NUM>,<NUM> and a second beam in the lower section with the sources <NUM>,<NUM>. The lamp according to this invention comprises a partition <NUM> for separating the first from the second beam, while the partition is having a first width a. It is worth of noticing that the partition as compared to other known system does not require of having a very sharp trailing edge. The lamp according to the invention comprises an offsetting element <NUM> that offsets the beam of the light of the second beam in direction essentially vertical towards while maintain its essentially horizontal alignment. The beam offset c from the offsetting element <NUM> is calculated by the law of refraction and depends on the offsetting element <NUM> thickness b, an angle α of the offsetting element <NUM> with respect to the beam direction and refractive index n of the transparent material used to manufacture the offsetting element <NUM>, where n is a material constant. The gained beam offset c is preferably equal or greater than the first width a of the partition <NUM>. The required beam offset or the second width c can be calculated according to the following formula: <MAT> where:.

The offsetting element <NUM> is placed in the second beam and shaped in such a way that it does not affect the direction of the first beam. The offsetting element <NUM> is a glass prism with two parallel first faces. The offsetting element <NUM> has the width b, and has a second face which is formed so that it does not obstruct the first beam. When the offsetting element <NUM> is angled towards the light of the second beam with the sources <NUM>, <NUM> creates a light path that is offset by the beam offset c in a direction which compensates the obstruction created by the partition <NUM>. The subdivided sections from the intermediate image are projected in the approach or in pilot's direction <NUM> by means of a lens <NUM>.

This results in a device that emits a beam which is split horizontally and consisting of radiation of the first wavelength e.g., a white light in the higher section and forms the first beam and the radiation of the second wavelength e.g. a red light in the lower section that forms the second beam. The pilot sees either red or white light from one particular lamp module. In case of following the infrared signals with the help of night vision goggles, the pilot can distinguish the two infrared signals by means of the transmitted temporal signal, for instance steady or flashing.

Tilt and position of the offsetting element <NUM> can be adjusted, the position of the partition <NUM> can also be adjusted. The advantageous effect of positioning the two elements <NUM> and <NUM> is that the width of a possibly overlapping area of the first light beam and the second light beam can be minimized.

In one of other embodiments the offsetting element can be a composite material having at least two layers of materials with a different refraction index n1 and n2 of a different thickness b1, b2. In general, the offsetting element <NUM> can be made of many different layers each of a different refraction index and thickness.

The formula for calculating the second width c is as follows: <MAT> where:.

Claim 1:
A lamp for a precision approach path indicator comprising
at least two radiation sources (<NUM>, <NUM>, <NUM>, <NUM>) emitting electromagnetic radiation of different wavelengths, a beam of a radiation of a first wavelength (<NUM>,<NUM>) and a beam of a radiation of a second wavelength (<NUM>, <NUM>),
a partition (<NUM>) for separating the beam of the radiation of the first wavelength (<NUM>, <NUM>) from the beam of the radiation of the second wavelength (<NUM>, <NUM>), while the partition (<NUM>) is having a first width (a),
wherein
the lamp is further provided with an offsetting element (<NUM>) that offsets at least one of the beams towards the other of the beams by a second width (c) to compensate the obstruction created by the partition (<NUM>),
characterized in that wherein the offsetting element (<NUM>) is a glass prism with two parallel first faces of a width (b), so that when the offsetting element (<NUM>) is angled towards the beam of the second wavelength (<NUM>, <NUM>) it creates a light path that is offset by the first width (a) of the partition (<NUM>), and with at least one second face angled in respect of the parallel first faces so when the offsetting element (<NUM>) is angled towards the beam of the second wavelength (<NUM>, <NUM>) the second face is parallel to and below the beam of the first wavelength (<NUM>, <NUM>).