Abstract:
An airport feature display system for aircraft provides visual guidance cues and awareness to track the specified taxi path on a HUD. The guidance cues include symbology representative of the position of selected airport features such as runway and taxiway edges, taxi routes, and airport signage. Data representative of the airport features is communicated between aircraft systems using a data interchange method that facilitates efficient throughput of the large quantities of data required to represent the airport features.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Nos. 60/336,752; 60/337,182; 60/337,192; and 60/337,295, all filed Dec. 4, 2001, the disclosures each of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to aircraft surface guidance systems (SGS) and, in particular, to a communications interchange for transmitting airport feature data to a conformal display system (e.g., head-up display (HUD)) on an aircraft. 
     2. Technical Background 
     There is considerable interest in enhancing surface guidance for aircraft. After an aircraft lands on a runway at an airport, the next step is to taxi the aircraft to a desired destination such as a passenger-loading/unloading gate. A pilot can easily become confused or lost amid the many runways, taxiways, ramps, and buildings that make up an airport. The problem is more significant at large airports and is particularly significant at night when the multitude of lights can make it more difficult to taxi the aircraft to the desired destination. 
     Efficient taxi operations save time and money. With airports becoming more crowded, aircraft often spend considerable time taxiing between runways and gates. Taxi time is even longer if the pilot makes a wrong turn, becomes lost, or blunders onto the wrong runway or taxiway. In addition, a wrong turn or navigation blunder can cause delays for other aircraft at the airport. 
     One feature of an airport surface guidance capability is the presentation of airport features such as runways and taxiways that are readily made available to the pilot. One approach to present such feature information is on a head-up display (HUD) that is displayed in the forward line of sight of the pilot looking out the front windshield of the aircraft. The pilot typically enters or selects a taxi path that has been approved by ground controllers. The taxi path or route is then displayed on the HUD. The pilot can view the features displayed on the HUD as being overlaid on the surface features the pilot can normally see through the windshield. However, in poor visibility conditions, the pilot can still view the airport features displayed on the HUD. The airport features give a pilot situational awareness of where the aircraft is relative to the selected taxi path. 
     A key aspect to a practical avionics implementation for surface guidance must generally include a communications bus or data link for transmitting the large amounts of data required to adequately represent airport features on a display screen. An obstacle for the practical implementation of an airport feature display system is the requirement to clearly display airport features, preferably with taxi instructions and other useful symbology conformal to the pilot&#39;s view out the front windshield. Data representing airport features can also consume large amounts of memory. The problem is more acute since the data for many airports must be stored in memory. In addition, prior airport feature display systems require a correspondingly high-speed communications bus to transmit the airport feature data to a display system (e.g., HUD). This requirement, coupled with the fact that many avionics systems have limited data storage capability and do not have high-speed buses, have stymied efforts to implement airport features on the existing HUD systems on many aircraft. One approach for displaying airport features has been to upgrade aircraft avionics systems with new equipment that has large data storage capability and high speed data buses. However, these systems must be designed, certified, integrated with the exiting avionics suite, and installed. All this makes such an upgrade very costly and, therefore, this approach is economically infeasible for many aircraft. 
     Any airport feature display system should be adequate not only to accomplish the task of displaying airport features, but to also make the displayed features useful and the system cost-effective. It is also desirable to design an airport feature display system that may be retrofit into existing aircraft avionics systems at minimal cost. 
     The continuing goal, therefore, is to find ways to reduce costs, reduce taxi errors, reduce taxi time, and improve airport efficiency. 
     SUMMARY OF THE INVENTION 
     To address the goals stated above and other goals, the inventive airport feature display system comprises a unique data interchange method for facilitating the commnunication of airport feature data through conventional data buses without the need to design or install new high speed data buses. For retrofit applications, the airport feature display system is compatible with many existing HUD systems with minimal modification. 
     According to one aspect of the present invention, the airport feature display system is integrated as an extension of the flight management system (FMS) which provides the enroute planning function for the aircraft. The FMS is already installed in many aircraft and the FMS comprises many of the components required to implement the airport feature display system of the invention. For example, an FMS comprises a processor, data storage devices, a user interface, and is in communication with multiple display systems such as a HUD. 
     Another aspect of the invention is reduced bandwidth requirements for communicating the data representative of airport features to the HUD. This is important for implementing a cost-effective feature display system on existing aircraft. Many existing communications buses between an FMS and a HUD do not have sufficient bandwidth to communicate the feature data. One example of such a bus is the electronic flight instrument system (EFIS) bus that typically communicates data between the FMS and the HUD. The present invention significantly reduces the necessary bandwidth. A high-resolution position coordinate for an airport monument is transmitted to the HUD. A high resolution coordinate requires two words of Aeronautical Radio, Inc. (ARINC) data. The invention transmits the remaining data coordinates as one word that represent a high resolution position, but are referenced to the airport monument (i.e., reference point). The invention thereby effectively reduces the required bandwidth by approximately one half. This is sufficient to enable the use of existing communication buses and significant cost savings. 
     It is clear that the invention is a significant improvement over the prior art systems. Further, those skilled in the art recognized that the invention is not limited to use with an FMS. Other processors, display screens, and data entry devices may be used to practice the invention. 
     Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described in the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description, serve to explain the principals and operation of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of one embodiment of an airport feature display system according to the invention; 
     FIG. 2 is a sample airport feature display on a HUD screen; 
     FIG. 3 is a sample airport reference location format according to the invention; 
     FIG. 4 is a sample taxi path format according to the invention; 
     FIG. 5 is a taxi path segment corresponding to the taxi path sample of FIG. 4; 
     FIG. 6 is a flowchart of an algorithm for computing the relative latitude/longitude coordinates of airport features according to the invention; and 
     FIG. 7 is a sample airport signage and surface identification format according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
     An exemplary embodiment of the airport feature display system according to the present invention is shown in FIG. 1, and is designated generally throughout by reference numeral  10 . The components of the airport feature display system of the present invention will first be briefly described and then described in detail. The most common use for the invention is as an integrated element in the existing FMS and HUD of an aircraft, such as a commercial passenger or cargo jet, and therefore the following discussion will describe the invention in relation to such an application. 
     Referring to FIG. 1 there is shown a block diagram of an airport feature display system according to the invention and related aircraft systems. All of the aircraft systems can comprise the invention and, therefore, they are collectively referred to as airport feature display system  10 . Airport feature display system  10  comprises flight management computer (FMC)  11 , multifunction control display unit (MCDU)  12 , navigation database (NDB)  13 , head-up display (HUD)  14 , electronic flight instrument system (EFIS)  15 , multi-mode receiver (MMR)  16 , transponder  17 , and communications management unit (CMU)  18 . FMC  11  and MCDU  12  are generally referred to collectively as a flight management system (FMS). 
     FMC  11  comprises a processor  11 A, and memory  11 B. Processor  11 A may include any data processor suitable for receiving and processing commands and data. Processor  11 A is preferably a microprocessor with sufficient data processing power to complete the required FMS and airport features tasks in real-time. Memory  11 B preferably comprises both random access memory (RAM) for storing dynamic data and variables, and read-only memory (ROM) for storing program data and static data. Processor  11 A communicates with memory  11 B to retrieve program instructions and data and to manipulate and store and retrieve variables. Processor  11 A is also in communication with NDB  13 . 
     NDB  13  comprises airport and taxi route data describing airport runways, taxiways, gates, ramps, standard taxi routes and various other airport structures and desired features. The airport data  13 A is preferably stored as a linked list and standard taxi routes  13 B are also stored in the database. However, the data may also be stored in many other formats as desired. NDB  13  is preferably rewritable or replaceable so that the airport data and standard taxi route data is easily updated as needed and so that the data remains current regarding changes to airport runways, taxiways, construction, and the like. NDB  13  is constructed of any of various memory storage technologies such as PROM, EPROM, EEPROM, magnetic disk drives, optical disk drives, or various combinations of these and similar devices. The operative requirement merely being the capability to store the airport data. 
     The user interface is preferably accomplished through MCDU  12  which communicates with FMC  11  and processor  11 A. MCDU  12  comprises a display screen  12 A, line select keys  19 , and a key pad  12 B. MCDU  12  is commonly used to enter enroute flight planning commands to the FMC  11  and to output enroute flight data to the pilot, crew, or operator via display screen  12 A. The operation of line select keys  19  allow quick selection and deletion of displayed items. The invention preferably uses this preexisting user interface device to accomplish the user interface for ground navigation at airports, although other user interfaces may also be used to practice the invention. For example, other displays such as the EFIS  15  or HUD  14  may be used as part of the user interface if desired. 
     HUD  14  and EFIS  15  are shown in communication with FMC  11 . HUD  14  projects an image to a combiner positioned along the forward line-of-sight of the pilot such that a pilot can view the image and simultaneously look out the front windshield of the aircraft. EFIS  15  (also referred to as a head-down display (HDD)) is typically positioned below the front windshield of the aircraft. EFIS  15  comprises one or more display screens which are typically implemented using cathode ray tubes (CRTs), flat panel displays, or functionally similar display devices. The airport features are preferably displayed to the pilot on the HUD  14  which is the display of choice for this type of conformal display. The EFIS  15  may be used also. The EFIS  15 , HUD  14 , and MCDU  12  each have display screens that may be used to practice the invention. 
     Several communications systems are also coupled to the FMC  11 . MMR  16  receives navigation or position signals such as global positioning system (GPS) signals, differential GPS (DGPS), local area augmentation system (LAAS) signals, wide area augmentation system (WAAS) signals, and the like. These signals are communicated to the FMC  11  where the position of the aircraft is determined. This aircraft position information, or similar information from other sources, is then used to compute appropriate airport feature data or is communicated to other aircraft systems. 
     Transponder  17  and CMU  18  provide additional input and output communications channels. Transponder  17 , for example, may receive signals such as automatic dependent surveillance broadcast (ADS-B) from other aircraft or from air traffic control (ATC). This information may be used to add symbology indicative of other vehicle&#39;s location and movement to the airport features display. CMU  18  comprises a data link with ATC or similar controlling authority through which taxi routes, plans, and instructions are communicated, negotiated, modified, and approved or denied. 
     There exist many communications standards in the aviation community, and particularly in the field of avionics. Aeronautical Radio, Inc. (ARINC), of 2551 Riva Road, Annapolis, Md., publishes a variety of standards relating to aircraft avionics. Two such publications disclose aviation communications standards. ARINC 429 is a standard relating to a communications bus frequently used on aircraft. ARINC Characteristic 702A is entitled “Advanced Flight Management Computer System” was published Dec. 31, 1996, and relates to, among other things, the communication protocols between an FMS and a display system. Both of these publications are hereby incorporated by reference. 
     FIG. 2 is a sample display of airport feature symbology on a HUD according to the invention. Looking through the combiner  21 , which is the display screen of a HUD system, the pilot views the paved runway  22 , the runway edge  22 A, the runway centerline  22 B, and the turnoff or taxiway connector  23  pavement. The airport feature symbology displayed on screen  21  comprise runway and taxiway edge cones  24  and taxi path symbols  25 . Other displayed symbology comprises flight path guidance cue  26 , ground speed  26 A, target speed  26 B, next turn indicator with distance readout  26 C, main gear envelope symbol  26 D, and heading  26 E. Symbology is preferably conformal with the ground features. 
     The symbology displayed using the airport feature data depicts the pavement outlines of the runway and taxiways. The positions (i.e., position locations or coordinates) of the symbology are absolute latitude/longitude coordinates using twenty (20) bits of data in the BNR format that is referenced in the ARINC specifications. It will be noted that twenty (20) bits of data occupies one word in the ARINC format and is not considered high resolution for such an application. The ARINC specifications provide for more accurate latitude/longitude values that occupy two words in the format. However, it was found that transmitting all of the airport feature data in a high resolution format requires too much bandwidth on most buses. The instant invention solves this problem by communicating one high resolution coordinate/position to the HUD  14  and computing the remaining symbology location points to be relative to the one high resolution coordinate. It is preferred that the high resolution coordinate is a fixed location or monument on the airport. Therefore, the remaining airport feature data is computed to be positioned relative to the airport monument or reference data  30 . Using this technique substantially reduces the required bandwidth to transmit airport feature data and enables the airport feature display system to be practiced on many avionics systems currently in service. 
     FIG. 3 illustrates a sample format for such an airport monument or reference data  30 . The high resolution latitude data for the monument is transmitted in words 1 and 2 of the reference data  30 . Next, the high resolution longitude for the monument is transmitted in words 3 and 4 of the reference data  30 . Finally, if an airport ID is desired, four ASCII characters are transmitted in words 5 and 6 of the reference data  30 . Airport elevation may also be transmitted in the reference data  30 , but it is available from the FMS database or other sources and these other sources are preferred to save bandwidth on the communications bus. 
     FIG. 4 illustrates a sample format for transmitting airport feature data to a HUD according to the invention. The relative X, Y, Z data referred to as words 1-3 in the table  40 , are formatted single word data values. However, the HUD  14  translates these low resolution format data values into high resolution position locations or coordinates by combining the low resolution format data values with the airport monument or reference data as is described below in reference to FIG.  7 . According to one embodiment, using the relative position of the data points reduces by approximately one half the number of data words required to specify a location point or coordinate. This equates to a reduced bandwidth required to transmit the data. The data in table  40  corresponds to the taxi path diagram in FIG.  5 . Only three words  41 A,  41 B, and  41 C are needed to specify the location and elevation of point A1. Similarly, only three words are needed to specify the location and elevation of points A2, B1, and B2. Using the present invention, high resolution coordinates are communicated across data buses using one half the bandwidth normally required. 
     Referring to FIG. 5 there is shown a representative taxi path that is initially described in table  40 . Segment A is defined by words 1-6 in table  40 . Conic B is defined by words 10-12 in table  40  and segment B is defined by words 13-18 in table  40 . 
     FIG. 6 is a flowchart of a process for computing the relative position of the X (longitude), Y (latitude), and Z (elevation) coordinates for airport features. Starting in block  60 , the process proceeds to blocks  61  and  62  where the latitude and longitude high resolution airport monument data is received and the latitude and longitude high resolution point of interest data is received. Δ(Delta) lat. is computed as the difference between the latitude of the point of interest and the latitude of the airport reference or monument in block  63 . The similar computation is done in block  64  for Δlon. Next, the relative latitude is computed using the formula in block  65 . The relative longitude is computed using the formula in block  66 . Finally the relative elevation, or elevation, is computed using the formula in block  67 . With the relative position point computed, the data is loaded into an appropriate format and transmitted to the HUD. 
     Referring to FIG. 7 there is shown another example of the format of the current invention. Table  70  comprises two data words representing the X and Y coordinates for signage. For signage and certain other features, no elevation value is required and the additional bandwidth is preserved for other uses. 
     It will become apparent to those skilled in the art that various modifications to the preferred embodiment of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.