BACKGROUND OF THE INVENTION

This invention is directed to aviation safety and control equipment, and is more specifically concerned with ground-based runway approach equipment for visual assistance to the airplane pilot in safely landing the airplane. The invention is more particularly concerned with an improved precision approach path indicator system, i.e., PAPI system. Such system is positioned at an approach end of an airport runway and provides visual aid to a pilot landing the aircraft by indicating the plane's position relative to a predetermined glide path.

Precision approach path indicators, or PAPI, are discussed in Advisory Circular AC NO. 150/5345-28H (Jul. 29, 2019) promulgated by the US Federal Aviation Administration.

The PAPI system typically consists of four light units arranged in a line transverse to the runway center line at the target landing point on the runway, with the light units usually being disposed to the left of the runway.

Each light must provide a beam of light split horizontally with aviation-white light in the top sector (above the horizontal split line or transition line) and red light in the bottom sector. To ensure a sharp division between red and white sectors when the PAPI light unit is viewed from 1,000 feet (300 meters) the transition from red light to white light must be within 3 minutes of arc at the beam center, and within 5 minutes of arc at the beam edges. The transition band must be essentially flat within 3 minutes of arc.

Originally, PAPI units used incandescent halogen lamps as their light sources. However, due to considerations of power usage, lamp-life ratings, and heat issues, alternative light sources, e.g. LED's, are more attractive for newer PAPI units. Proper chromaticity can be achieved using LED's as alternative light sources. Testing has shown that both for pilots with normal color vision and for color-vision waived pilots (having some color vision deficiency) the pilots will perceive the same color transition on red and white LED PAPI systems as with traditional incandescent PAPI systems. However, in order to achieve sufficient luminous intensity from an LED light source, it is necessary to employ an array of a multiplicity of LEDs, and not a point light source, or a COB which is an array of LEDs configured as a single light source. Accordingly, it has been difficult to achieve the required red-white transition within the maximum allowed 3 minutes of arc.

Prior LED-based PAPI units are discussed, e.g., in Hansler U.S. Pat. No. 8,550,658, Tian U.S. Pat. No. 8,434,905, and Kaminski U.S. Pat. No. 7,375,653. Kaminski requires a pair of reflective surfaces that angle together and form a sharp edge, with the two surfaces reflecting light from a bank of red LEDs and a bank of white LEDs, respectively. The reflected light proceeds to a collimator lens or projection lens. The Kaminski unit also uses a lateral spreader lens. The Hansler PAPI unit has a single array of LEDs, a horizontal blade positioned between red and white LEDs, and first and second focusing lenses along the same optic axis. The Hansler unit also incorporates a light detection and feedback circuit to control the LED lamp intensity. Other equivalent light sources such as solid-state lasers, and VCSELs (vertical surface emitting lasers), are now or will be available in future, but for convenience's sake the term LED will be used in this specification and in the claims to cover all such devices.

OBJECTS AND SUMMARY OF THE INVENTION

It is an important object to provide an LED-illuminated precision approach path indicator or PAPI arrangement that is simplified in construction and provides a sharp, flat transition between the red and white beam portions to provide pilots an accurate indication of their actual approach relative to the approach path for safe descent to the airport.

It is another object to provide an LED-illuminated PAPI arrangement that is constructed with a single collimator lens per beam.

A further object is to optimize the sharpness of transition between red and white sectors.

In accordance with an embodiment of this invention, a precision approach path indicator (PAPI) device is configured to project a beam of light along an airport runway glide path that transitions from a first color to a second color when a plane moves above or below the runway glide path. The current convention is that the two colors are red and white, but the color scheme can change depending on application. In this invention, the PAPI device has a case or housing, with a light source within the housing. Here the light source has first and second arrays of LEDs, i.e., an array of red LEDs and an array of white LEDs. The two arrays are disposed one above the other and generally in a vertical plane defining a generally horizontal axis normal to the arrays, such that the arrays emit light along that axis. A collimating lens of a predetermined width and height has a predetermined focal length f, and has an optic axis aligned with the axis of the light source. The collimating lens is spaced distally from the light source. Also along the optic axis of the lens there are first baffle or aperture plate and (preferred, but optional in some cases) second baffle or aperture plate, each being a respective frame with a cut-out defining an aperture for shaping the light passing along the optic axis. The first frame is positioned between the light source and the collimating lens at a distance from the lens substantially equal to the lens's focal length f. The first frame has a horizontally elongated cut-out or aperture. The second frame (when used) is positioned at the collimating lens and covers top, bottom, and side edge portions of the lens. This second frame has a horizontally elongated aperture. A planar blade extends from the light source to the first frame and has a proximal edge positioned between the first and second arrays of LEDs. This blade also has a distal edge extending across the aperture of the first frame so that the first frame is substantially at the focal distance f from the collimating lens. The blade divides the beam into white and red sectors at the plane of the first frame. The planar blade may have reflective upper and lower surfaces. One or more intermediate frame(s) can be positioned at suitable positions between the first and second frames along the beam axis (or between the first frame and the collimating lens).

The second frame in the below-described embodiment(s), here adjacent the collimating lens, helps to block light from the light source from reaching upper and lower sectors of the collimating lens at its edges and from reaching left and right sectors at the edges of the collimating lens. This arrangement permits the light to reach the lens at an elongated central portion defined between the upper, lower, right and left sectors at the edge of the lens.

In one described embodiment, a tubular or box-like shell surrounds the light beam and encloses the optic axis between the light source and the lens, with its ends joined with the first and second frames. The shell can have generally flat sides on top, bottom, left and right defining a generally rectangular section; the shell is opaque and generally non-reflective. In a preferred arrangement, the aperture of the first frame has a width substantially one-and-one-half to two-and-a-half times its height. The aperture of the second frame can have a horizontally elongated octagonal shape, and favorably has an aperture where the height may be about a given fraction of its width. That is, the apertures may be horizontally elongated to be about 1.5 to 2.5 times as wide as they are tall. While the apertures may be rectangular, they may also be octangular, ellipsoial, or a similar shape. The baffles or frames and their apertures are calibrated to match the particular lens or lens group that is used in the PAPI device for optimal beam separation.

The two arrays of LEDs of the light source respectively emit light of the first and second colors, and are each formed as a plurality of horizontal rows of LEDs that emit light of the respective color (although, the white light may be generated either by white LEDs or by a mixture of LEDs of the primary and complementary colors as needed to constitute white light). The arrangement is not limited only to horizontal rows of LEDs, as these may be placed in other arrangements, e.g., designed for optimal illumination. The planar blade is disposed on a substantially horizontal plane situated between the lowest row of the first array and the uppermost row of the second array. This results in one color, e.g., red being entirely above the blade and the other e.g., white being entirely below the blade. The collimating lens directs the light along the optic axis on a beam in which the white light is above a horizontal transition and the red light is below the horizontal transition.

There are typically four of these PAPI devices arranged in a line that is transverse to the runway center line and off from one edge, e.g., left, of the runway edge. These are directed at successive angles so that for an aircraft approaching directly on the runway glide path, the two beams nearer the runway will appear red and the outer two will appear white, and the number or red and white beams will change depending on the height of the approaching airplane relative to the proper glide path.

These and other important features of the invention will become apparent from the ensuing description of a preferred embodiment, when considered in connection with the accompanying Drawing.

