Airborne system and method for improving the integrity of electronic landing aids

[0001] The invention relates to avionics, and more particularly, to a system that enhances the ability of an aircraft to land using an Instrument Landing System (ILS) or a GPS-based landing system.

[0002] The process of landing an aircraft on an airport runway requires a good degree of skill as well as knowledge of the aircraft's position with respect to the runway. A pilot must be aware of the aircraft's speed, direction, and angle of descent (known as the glideslope) with respect to the desired touchdown location on the runway. Improper landings may occur if inclement weather or poor visibility, for instance, impedes the pilot's awareness of one or more of these factors.

[0003] Because of the possible difficulties that may occur during landing, various systems have been devised to assist the pilot. One such system is known as the Instrument Landing System (ILS), which in its most basic form comprises a VHF localizer signal and a UHF glide slope signal that are transmitted from different positions adjacent the runway. A receiver onboard an airplane receives the signals, and the signals are converted into data usable to determine the position of the airplane with respect to the runway centerline as well as the glide path of the airplane. The ILS signals, which combined may be termed an ILS beam, thereby provide the pilot with critical information that may be used during a landing, even in low-visibility situations.

[0004] Many airports cannot afford the equipment necessary to fully implement the ILS system so that it may be used in all weather and visibility categories of approved landing approaches. Some of these airports have deployed a less expensive ILS system that emits a lower-quality beam known as a Type I ILS beam. A Type I ILS beam may be suitable for assisting pilots to land in relatively clear weather, but lacks the integrity necessary to be used in the lowest visibility and weather conditions. Because a Type I ILS beam is unverified, it is possible that the beam may transmit incorrect data, and reliance on the incorrect data in poor visibility may cause an unsafe landing if the pilot cannot otherwise verify the data given to him by the ILS beam. For this reason, a Type I ILS beam may not normally be used to direct a pilot during a CAT II (defined as requiring a runway visual range of >1200 feet and a decision height of 100 feet) or a CAT IIIa (defined as requiring a runway visual range of >700 feet and a decision height of 50 feet) approach. What is needed is some way of increasing the integrity of a Type I ILS beam so that the beam may be used in low visibility conditions such as a CAT IIIa approach.

[0005] Global positioning systems, which use a constellation of satellites to provide location coordinates of an object, show significant potential to improve some avionics functions. In the future, some airports may use GPS-based landing aids to provide ILS-like lateral and vertical deviations from a desired approach path. An independent means to verify the GPS-derived path is needed to improve the overall integrity of the system.

[0006] It is therefore an object of this invention to provide a system that increases the integrity of a navigational aid such as an ILS beam or a GPS-based landing system.

[0007] It is another object of the invention to provide a system that independently verifies data derived from a navigational aid.

[0008] One feature of the invention is the use of data from an imaging system to independently verify data from a navigational aid.

[0009] Another feature of the invention is the creation of a geometric construct, representing geometries sensed by an imaging sensor, and the derivation of an aircraft's glideslope and position relative to a centerline of an airport runway.

[0010] An advantage of the invention is that low-visibility CAT IIIa approaches may be performed at airports having Type I ILS systems.

[0011] Another advantage of the invention is that unsafe landings are significantly reduced.

[0012] The invention provides a method of increasing positional awareness of a pilot of an aircraft during a landing approach of the aircraft. According to the method, first data from a navigational aid is received. The first data is analyzed to determine a first position of the aircraft at a predetermined time. Second data is received. The second data is independent of the first data. The second data is analyzed to determine a second position of the aircraft at the predetermined time. The first position of the aircraft and the second position of the aircraft are compared, and the pilot is alerted to a difference between the first position of the aircraft and the second position of the aircraft.

[0013] The invention also provides a method of verifying the accuracy of a navigation signal used in a landing operation of an aircraft during a low-visibility approach. According to the method, a navigation signal is received. The navigation signal is analyzed to determine one of a first glideslope and a first position of the aircraft relative to a runway. An image of the runway is obtained from a sensor disposed onboard the aircraft. A geometric construct is derived based upon features of the runway detected in the image of the runway. The geometric construct is analyzed to determine one of a second glideslope of the aircraft and a second position of the aircraft relative to the runway. The method compares one of the first glideslope to the second glideslope, and the first position of the aircraft to the second position of the aircraft. An operator of the aircraft is alerted to a difference between one of the first glideslope and the second glideslope, and the first position of the aircraft and the second position of the aircraft.

[0014] The invention further provides a system for assisting an airplane pilot during a landing approach of the airplane. A receiver receives a navigation signal, which is analyzed to determine a first position of the airplane at a predetermined time. An image sensor obtains image of a runway. A processor derives a geometric construct based upon features of the runway detected in the image of the runway. The processor analyzes the geometric construct to determine a second position of the airplane at the predetermined time. A display displays the geometric construct so that the pilot may view the geometric construct during the landing approach. An alerting mechanism alerts the pilot to a difference between the first position of the airplane and the second position of the airplane.

[0023] Turning now to the drawings, in which like reference numbers designate like components, an embodiment of the invention is schematically shown in FIGS. 1–2, in which an airplane 10 is making a landing approach toward a runway 12. A VHF localizer transmitter 14 and a UHF glideslope transmitter 16 are situated adjacent runway 12 at predetermined positions. Together, transmitters 14, 16 comprise an instrument landing system (ILS) and transmit a combination of signals that for convenience will be hereinafter called an ILS beam. A receiver 18 is provided aboard aircraft to detect the ILS beam. As shown in FIG. 2, receiver 18 includes an antenna 20 and a tuner 22, and together the antenna and the tuner detect signals on frequencies upon which transmitters 14, 16 are transmitting. Signals detected by receiver 18 are sent to a flight computer 24, which includes a processor 26 and a memory 28. Processor 26 analyzes the detected signals and determines the position of the runway centerline and the glideslope of aircraft 10 relative to runway 12.

[0024] The invention also includes an image sensor 30 that is secured to the outside of airplane 10. Image sensor 30 is preferably a camera sensitive to the near infrared (IR) or to visible light. For example, the image sensor may use short-wave IR, mid-wave IR, long-wave IR, or millimeter (mm) wave radar technology. Image sensor 30 is aimed, either permanently or temporarily, to sense images directly ahead of and below airplane 10, and thereby captures an image 32 of runway 12 approached by airplane 10 (FIG. 3). As shown in FIG. 3, image 32 may include an unobstructed view of the entire runway 12, although it is not necessary for the entire runway to appear in image 32. Image 32 may also include all or part of the runway lighting that surrounds runway 12 or otherwise directs aircraft 10 toward the runway.

[0025] Image 32 is sent to flight computer 24, where processor 26 creates a geometric construct 34 having shapes and proportions corresponding to the shapes and proportions of image 32. As shown in FIG. 4, geometric construct 34 is a computer-generated, synthetic derivation or representation of image 32 detected by image sensor 30. During a landing approach, geometric construct 34 will be a derivation of the runway and/or the runway lighting as viewed by the airborne image sensor. Depending on the aircraft's position on the runway, geometric construct 34 may include a regular or irregular quadrilateral (or portions thereof whose shape varies depending on the aircraft's position relative to the runway.

[0026] Once geometric construct 34 has been created by processor 26, the geometric construct is analyzed to determine the airplane's glideslope and lateral position relative to the runway centerline. Various algorithms and methods may be used to determine the airplane's lateral position and glideslope, such as one or more of the following: comparing the length of one of the sides with a corresponding dimension of the runway, which may also be stored in memory; analyzing the relative length of opposite sides of geometric construct 34; determining if geometric construct 34 is symmetrical along an arbitrary or a predefined centerline; determining the position of some or all of the geometric construct (which would correspond to whether the position of runway 12 as sensed in image 32 is centered); and calculating one or more angles of the geometric construct. In addition, if an image is periodically sensed by image sensor 30 each second, for example, multiple geometric constructs may then be analyzed to determine any time-dependent change of the airplane's position. The details of these or other algorithms that use the geometric construct to determine airplane position are considered to be fully derivable, without undue experimentation, by one having ordinary skill in the art.

[0027] Processor 26 compares centerline position (i.e., the position of the aircraft relative to the centerline) and glideslope data derived from image 32 with centerline location and glideslope data derived from the ILS signal. Since the two sets of data are derived independent of each other, agreement of the data with respect to the centerline position and glideslope of the airplane causes processor 26 to conclude that the data, especially the ILS-derived data, is correct, and that the pilot may safely rely on the ILS-derived data to land the airplane. If there is any difference beyond a predetermined threshold between the two independently derived sets of data, it is assumed that one of the sets of data is incorrect. An alert 44 is provided to the pilot to warn of possibly incorrect data. Alert 44 may be visual, aural or tactile, and preferably advises the pilot to abort the current approach. The aircraft is directed to attempt another approach.

[0028] FIG. 5 is a flowchart showing a method 50 of practicing the invention. For convenience, method 50 will be described with reference to the above description of the invention, although the scope of method may in fact be broader than what has been described. In step 52, the method is initiated either manually by a pilot or automatically by flight computer 24 during a landing approach. In step 54, ILS data is received and processed by flight computer 24 (including processor 26) to determine centerline position and glideslope data. In step 56, image sensor 30 obtains image 32, which during a landing approach should include a view of runway 12 at an airport. In step 58, flight computer 24 (including processor 26) creates a geometric construct derived from image 32. In step 60, the geometric construct is analyzed, using one or more of various algorithms, to determine the centerline location and glideslope of airplane 10 relative to the runway. In step 62, the centerline and glideslope data derived using image sensor 30 are compared to the ILS-derived centerline and glideslope data. If there is no appreciable difference between the two sets of data, then in step 64 it is determined that it is permissible to use the ILS-derived data. However, if there is an appreciable difference between the two sets of data, then in step 66 the pilot is alerted that there is a discrepancy in the data. The pilot may also be instructed not to land using the ILS-derived data.

[0029] It is anticipated that in low-visibility landing scenarios not all of runway may be visible to image sensor 30. However, many of the above algorithms are designed to provide accurate aircraft position information even if the image sensor senses only a part of the runway.

[0030] The invention may advantageously be used to enhance the vision or awareness of a pilot landing in low-visibility conditions. To that end, part or all of the geometric construct may be presented to the pilot on an avionics display, and preferably is overlaid on the pilot's view of the runway using a head-up display (HUD) 40. The pilot would then have the benefit of enhanced awareness of the runway at a time when poor visibility prevents a clear, unaided view of the runway. FIG. 6 shows a method 70 according another embodiment of the invention in which, in step 72, the geometric construct is displayed on a HUD. Method 70 is otherwise substantially the same as method 50, which is depicted in FIG. 5.

[0031] The invention may be incorporated to verify the accuracy position and attitude data received from other types of precision navigation aids such as global position satellite-based (GPS) navigation aids. FIG. 7 shows a system 80, similar to the system shown in FIG. 2, in which receiver 18 is replaced by a GPS receiver 18a. GPS receiver 18a includes an antenna 20a and a tuner 22a, and together antenna 20a and tuner 22a detect signals on frequencies upon which GPS satellites (not shown) are transmitting. Signals detected by receiver 18a are sent to a flight computer 24, which includes a processor 26 and a memory 28. As with previously disclosed embodiments, processor 26 analyzes the detected signals and determines the position of the runway centerline and the glideslope of aircraft 10 relative to runway 12. The remaining components of system 80 are similar to those shown in FIG. 2.

[0032] System 80 may be operated according to the method 82 shown in FIG. 8 in flowchart form. For convenience, method 82 will be described with reference to the above description of the invention, although the scope of method may in fact be broader than what has been described. In step 83, the method is initiated either manually by a pilot or automatically by flight computer 24 during a landing approach. In step 84, data from a GPS-based landing system (GLS) is received and processed by flight computer 24 (including processor 26) to determine centerline position and glideslope data. In step 86, image sensor 30 obtains image 32, which during a landing approach should include a view of runway 12 at an airport. In step 88, flight computer 24 (including processor 26) creates a geometric construct derived from image 32. In step 90, the geometric construct is analyzed, using one or more of various algorithms, to determine the centerline location and glideslope of airplane 10 relative to the runway. In step 92, the centerline and glideslope data derived using image sensor 30 are compared to the GLS-derived centerline and glideslope data. If there is no appreciable difference between the two sets of data, then in step 94 it is determined that it is permissible to use the GLS-derived data. However, if there is an appreciable difference between the two sets of data, then in step 96 the pilot is alerted that there is a discrepancy in the data. The pilot may also be instructed not to land using the GLS-derived data. As with other embodiments of the invention, to assist the pilot the geometric construct may be displayed on an avionics display such as HUD 40.

[0033] An advantage of the invention is that ILS-derived data is verified by an independently-derived navigation aid, such as an IR imaging sensor or a GLS, either of which may be usable in low-visibility conditions.

[0034] Another advantage is that the system allows low-visibility approaches, such as CAT IIIa approaches, to be performed at the many airports that have ILS systems transmitting Type I beams.

[0035] Still another advantage is that a pilot may be more confident in ILS or GLS data provided during a landing approach, even if the pilot cannot visually confirm the accuracy of the data.

[0036] While the invention has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the invention includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. No single feature, function, element or property of the disclosed embodiments is essential to all of the disclosed inventions. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.

[0037] It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to the disclosed inventions and are novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the invention of the present disclosure.