Aircraft boundary transition warnings and auto alerting

Abstract

In combination with a Geographic Information System (GIS), 3-dimensional shapes may be used to designate or identify blocks of airspace. These shapes may be defined in many ways including lat/long, local coordinates, or FAA transmitted directions for TFRs and ADIZs. These restricted areas and zones may be modeled using suitably modified AirScene™ software from Rannoch Corporation. AirScene™ software can locate various aircraft in the vicinity of restricted airspace, determine whether the aircraft is about to enter restricted airspace, and issue a warning to the pilot of such aircraft that restricted airspace is about to be violated. Such a warning can be audible (e.g., radio communication message) or visual (e.g., graphic display or even a flashing light or text message) and is much less distracting than having a laser shining in the cockpit. Since the AirScene™ system is ground-based, ground personnel can also be advised if restricted airspace is being violated, or even about to be violated.

Description

FIELD OF THE INVENTION

The present invention relates to an aircraft tracking and warning system. In particular, the present invention is directed toward a system for detecting aircraft position relative to restricted airspace and providing graphical data to a pilot and/or a warning to inform the pilot of the position of the aircraft relative to restricted airspace.

BACKGROUND OF THE INVENTION

Since Sep. 11, 2001, it has become common practice for air traffic control authorities, militaries, and other organizations to restrict airspace use. In the United States airspace may be restricted through the use of Temporary Flight Restrictions (TFR) and Air Defense Identification Zones (ADIZ). Similar practices are employed in other countries. For background and several references to TFRs and ADIZs please refer to http://www.aopa.org/whatsnew/notams.html. The use of TFRs and ADIZ by Government authorities has become more and more prevalent. TFRs and ADIZs are used continually to protect airspace in major events, ranging from major public/stadium events (e.g., NFL Super Bowl) to affairs of state (Presidential events, visiting dignitaries, and the like). Thus, it may be difficult for pilots to keep up with the latest locations of TFRs and ADIZs.

The following is an excerpt from the Airplane Owners and Pilots Association (AOPA) Website cited above and incorporated herein by reference. As can be appreciated by one of ordinary skill in the art, understanding the nature and scope of this ADIZ can be difficult, even for a skilled pilot:

• • THE WASHINGTON DC METROPOLITAN AREA AIR DEFENSE IDENTIFICATION ZONE (DC ADIZ) FOR PURPOSES OF THIS NOTAM ONLY, IS THAT AREA OF AIRSPACE OVER THE SURFACE OF THE EARTH WHERE THE READY IDENTIFICATION, LOCATION, AND CONTROL OF AIRCRAFT IS REQUIRED IN THE INTERESTS OF NATIONAL SECURITY. SPECIFICALLY, THE DC ADIZ IS THAT AIRSPACE, FROM THE SURFACE TO BUT NOT INCLUDING FL180, WITHIN THE OUTER BOUNDARY OF THE WASHINGTON DC TRI-AREA CLASS B AIRSPACE AREA; AND THAT ADDITIONAL AIRSPACE CONTAINED WITHIN AN AREA BOUNDED BY A LINE BEGINNING AT 383712N/0773600W; THENCE COUNTER CLOCKWISE ALONG THE 30-MILE ARC OF THE DCA VOR/DME TO 384124 N/0762548W; THENCE WEST ALONG THE SOUTHERN BOUNDARY OF THE WASHINGTON DC TRI-AREA CLASS B AIRSPACE AREA TO THE POINT OF BEGINNING.

FIG. 4 is a graphical plot of the DCA zones illustrating a sample Restricted Airspace in the Washington DC area. As can be readily appreciated from FIG. 4, the zones and geometry are quite complex and extensive. It may be quite difficult for a private pilot to understand the nature and extent of such zones and successfully navigate such areas without inadvertently entering into such zones. As a result, in many recent incidents, small aircraft pilots have strayed into such restricted airspace, causing some panic and also risking the lives of the pilot and passengers, as well as those on the ground. Such inadvertent wanderings can create grave consequences for the pilot, including fines and possible suspension of licenses. In a worst-case scenario, the pilot could be shot down by surface-to-air missiles maintained by the military.

When planning any General Aviation (GA) flight, therefore, a pilot needs to check on all possible TFRs and ADIZs and other restricted airspace requirements anywhere near the flight plan. Since these can change on a day-to-day (or even hour-to-hour) basis, it may be almost impossible for a pilot to be aware of all airspace restrictions. On Feb. 6, 2005, for example, there were approximately 50 TFRs nationwide listed on http://map.aeroplanner.com, incorporated herein by reference. It can be difficult for the General Aviation pilot to keep up with all these constantly changing TFRs. From that same website, FIG. 8 illustrates TFRs for Super Bowl XXXIX on Feb. 6, 2005. Similar techniques may be applied to national defense, border security, and military test ranges. Test ranges usually have some form of aircraft tracking but do not provide automated transition warnings. FIG. 9 illustrates and an example of a test range for the U.S. Navy at Nanoose, near Vancouver, Canada. (See, http://www.rannoch.com/pdf/nanoose_—2520_—10_—01_—04.pdf).

Methods of warning aircraft of impending threats, such as an air-to-air collision include establishing a virtual bubble or envelope around the aircraft. These envelopes are sometime tiered to represent different severities of warnings. Two warning levels are represented in FIG. 10. The envelopes may be established based on distance or range/rate of closure. Examples of these techniques are found in Traffic Alert and Collision Avoidance Systems (TCAS) and Aircraft Alert and Collision Avoidance Systems (ACAS), as well as terrain avoidance systems including the following references, all of which are incorporated herein by reference:

• • U.S. Pat. No. 6,750,815 Method, apparatus, and computer program products for alerting surface vessels to hazardous conditions
  • U.S. Pat. No. 6,710,723 Terrain data retrieval system
  • U.S. Pat. No. 6,707,394 Apparatus, method, and computer program product for generating terrain clearance floor envelopes about a selected runway
  • U.S. Pat. No. 6,691,004 Method for determining a currently obtainable climb gradient of an aircraft
  • U.S. Pat. No. 6,606,034 Terrain awareness system
  • U.S. Pat. No. 6,571,155 Assembly, computer program product and method for displaying navigation performance based flight path deviation information
  • U.S. Pat. No. 6,477,449 Methods, apparatus and computer program products for determining a corrected distance between an aircraft and a selected runway
  • U.S. Pat. No. 6,469,664 Method, apparatus, and computer program products for alerting surface vessels to hazardous conditions
  • U.S. Pat. No. 6,445,310 Apparatus, methods, computer program products for generating a runway field clearance floor envelope about a selected runway
  • U.S. Pat. No. 6,380,870 Apparatus, methods, and computer program products for determining a look ahead distance value for high speed flight
  • U.S. Pat. No. 6,347,263 Aircraft terrain information system
  • U.S. Pat. No. 6,292,721 Premature descent into terrain visual awareness enhancement to EGPWS
  • U.S. Pat. No. 6,219,592 Method and apparatus for terrain awareness
  • U.S. Pat. No. 6,138,060 Terrain awareness system
  • U.S. Pat. No. 6,122,570 System and method for assisting the prevention of controlled flight into terrain accidents
  • U.S. Pat. No. 6,092,009 Aircraft terrain information system
  • U.S. Pat. No. 6,088,634 Method and apparatus for alerting a pilot to a hazardous condition during approach to land
  • U.S. Pat. No. 5,839,080 Terrain awareness system
  • U.S. Pat. No. 6,292,721 Premature descent into terrain visual awareness enhancement to EGPWS
  • U.S. Pat. No. 6,127,944 Integrated hazard avoidance system

The use of multi-layer threat analysis for terrain and aircraft collision detection, avoidance, and warning is therefore known in the art. However, to date, this technique has not been applied to the problem of warning pilots of aircraft intrusion into restricted airspace. FIG. 10 illustrates the two levels of Logic Showing Multiple Layers of Aircraft Protection and Alerting.

FIGS. 1 and 2 are diagrams illustrating the threat detection concepts of the TCAS system from a vertical and horizontal perspective, respectively. Referring to FIG. 1, a number of ranger criterion may be provided for the TCAS equipped aircraft. Such range criterion may include a surveillance range of approximately 20 nautical miles, a Traffic Advisory range of approximately 3.3 nautical miles, and a Resolution Advisory of approximately 2.1 nautical miles. An intruder aircraft entering into each relative range criterion may cause a corresponding advisory, warning, or indication to be generated to alert the pilot of the TCAS aircraft of the proximity of the intruder aircraft and/or provide instructions (e.g., “pull up!”) to avoid a potential collision.

FIG. 2 shows similar Altitude criterion, which are also used to indicate the relative threat level of an intruder aircraft. If the intruder aircraft is within 1200 feet of the flight level of the TCAS equipped aircraft, and is within the range criterion, a Traffic Advisory may be generated. If the intruder aircraft is within 850 feet of the TCAS equipped aircraft and within the range criterion, a Resolution Advisory may be generated.

Rannoch Corporation has been involved in the TCAS Independent Validation and Verification (IV&V) process since its inception in 1992. Its first task consisted in reverse-engineering version 6.04a of the TCAS logic,—correcting the original code and representing it using state chart diagrams (See, http://www.rannoch.com/Statechartf.html, incorporated herein by reference) and truth tables (See, http://www.rannoch.com/TruthTablef.html, incorporated herein by reference) reflecting the different conditions under which variables in the logic are assigned specific values.

The subsequent version of the logic, called “Change 7”, included the following additions. A refined “vertical tracker” used for altimetry, with a 25 ft quantization was added. A “horizontal miss distance filter” was included to suppress unnecessary alerts whenever the projected horizontal distance between two airplanes at closest point of approach is beyond a predefined threshold. A “multi-aircraft” capability was created, enabling the TCAS unit to choose the best escape maneuvers in a threat situation involving more than two aircraft.

Rannoch's verification of the logic featured the development of analysis tools for the TCAS SIMulation program (TSIM) and the design of logic-challenging aircraft encounter scenarios. See, e.g., Rannoch Demos at http://www.rannoch.com/demosf.html, and the TSIM software at http://www.rannoch.com/ZipFiles/tcasdemo.zip, both of which are incorporated herein by reference. TSIM's purpose is to test the TCAS logic, ensuring that its different representations, pseudocode and CRS (CAS Requirements Specifications), perfectly match. It comprises more than 300 encounter scenarios fully testing every part of the collision avoidance logic. Each scenario features “own” aircraft moving in a straight line and one or more “intruder” aircraft with a three-dimensional freedom of movement. As soon as an intruder aircraft becomes a threat, the CAS logic is activated causing own aircraft to climb or descend. Throughout the scenario, which can be displayed as seen from a plan or side view, relevant parameters of the encounter are recorded, facilitating further analyses.

Since Jan. 1, 1994, every aircraft carrying more than 30 passengers aboard is mandated by Congress to be equipped with a TCAS unit. As a direct consequence, major international airlines equipped their fleet with TCAS units, thus providing additional safety in other parts of the world. On an international level, the U.N. ICAO (International Civil Aviation Organization) is promoting the worldwide ACAS II (Airborne Collision Avoidance System) equipage of all aircraft with more than 30 passengers by Jan. 1, 2000, and its extension to all aircraft carrying more than 19 passengers by Jan. 1, 2005.

Future collision avoidance systems will benefit from the use of ADS-B (Automatic Dependent Surveillance—Broadcast) via the spontaneous transmission of data such as position, velocity, intent. It is expected that the former two will be based upon the Global Positioning System (GPS), providing users with as little as a sub-meter accuracy. The actual requirements needed to operate such a transition are under investigation by RTCA Special Committee 186, Working Group 4, which is supported by Rannoch Corporation.

FIG. 3 illustrates an enhanced TCAS system display from MITRE Corporation, with other traffic and weather information. TCAS targets are shown as diamonds, and range, heading, relative altitude, and ground speed are displayed.

As illustrated in the events of Sep. 11, 2001, Prior Art air traffic control systems are largely helpless if an aircraft turns off its transponder signal. The transponder outputs a signal identifying the aircraft and indicating its altitude based upon a barometric altimeter. Without altitude information, it can be difficult to properly track an aircraft and determine whether it has entered a restricted area, as these areas are often three-dimensional in shape. Barometric altimeters can be inaccurate, or spoofed, as the ground level pressure reading can be adjusted by the pilot. Thus, in addition to the other problems stated above, it remains a requirement in the art to provide an accurate method of determining an aircraft's altitude without relying upon the aircraft transponder.

Preventing pilots from breaking TFR and ADIZ boundaries is a constant challenge all over the United States and in other countries. The U.S. Government has been trying all types of solutions to prevent TFR and ADIZ “busts.” As described in the online aviation weekly AvWeb, the U.S. Government has recently experimented with lasers to deter pilots from entering restricted airspace. (see http://www.avweb.com/eletter/archives/avflash/335-full.html#188958)

NORAD has developed a “Visual Warning System” (VWS). NORAD is planning to shine lasers into a pilot's cockpit if the pilot “busts” the ADIZ around Washington, D.C. Red and Green lasers will be aimed into the cockpit of an aircraft entering the restricted airspace to warn the offending pilot of a violation of restricted airspace. A warning will also be broadcast on the ATIS if the event happens in the airport vicinity. As might be imagined, such a system has been met with some criticism, as the laser lights might arguably blind the pilot temporarily, thus leading to further confusion and violation of the airspace. An alternative to such drastic measures is needed.

Co-pending U.S. patent application Ser. No. 10/756,799 Filed Jan. 14, 2004 and incorporated herein by reference, discloses A Minimum Altitude Warning System is described to prevent Controlled Flight into Terrain (CFIT). In that patent application, a ground-based CFIT warning system provides pilots with CFIT alerts. The system is based upon a ground-based tracking system, which provides surveillance of aircraft, such as the AirScene™ multilateration system manufactured by Rannoch Corporation of Alexandria, Va. The system monitors both horizontal and vertical positions of aircraft. When an aircraft has been determined to be operating below safe altitudes, or too close to obstructions, the pilot is provided with a warning. The warning may be delivered via the pilot's voice communications and/or a data link or the like.

FIG. 5 illustrates the fundamentals of the AirScene™ method of tracking using triangulation or multilateration of the aircraft's transponder signals as is known in the art, although many other methods may be used to track an aircraft (e.g., radar and the like). In the embodiment of FIG. 5, radio signals emanating from aircraft on the ground 560 and in the air 510 may be received at a number of discrete receiver locations 520 spaced throughout the area of interest. The time stamps from these signals may be fed to a processor 540 where the Time Difference of Arrival (TDOA) can be used to calculate the position of aircraft 510 and 560 and display such information in graphical or numerical form on a display 530. Thus, it is possible to precisely locate the position of an aircraft using radio signals emanating from the aircraft or by other means.

Other means of tracking include radar systems and ADS-B. Many countries are implementing a network of ADS-B ground stations as described in the following references:

• • http://www.raytheon.co.uk/highlights/ATMS.html
  • http://www.raytheon.co.uk/news_room/news/press_—02022005.pdf
  • http://www.airsysatm.thomson-csf.com/products/NAV/ads_b.htm
  • http://www.eurocontrol.be/care/asas/tn-workshop1/asas-tn-vanderkraan2.ppt
  • http://www.eurocontrol.be/care/asas/tn-workshop1/asas-tn-howlett.ppt

An alternative to shining lasers into the cockpits of aircraft that stray into restricted airspace is needed. The only other alternative—shooting down such aircraft—is also unacceptable. Thus, a need exists in the art to provide a system for warning pilots that they are about to enter restricted airspace before they enter such airspace, without blinding them or otherwise distracting them from flying.

As illustrated herein, techniques exist in the art for precisely locating the position of aircraft relative to one another and relative to the ground and positions within the airspace. As also noted herein, communications, warning, and graphical display devices already exist in the cockpit to display the relative position of an aircraft and/or warn a pilot of the position of the aircraft relative to another aircraft, the terrain, or an obstacle. Such a system should also be capable of warning personnel on the ground of an aircraft entering restricted airspace. It remains a requirement in the art to combine these existing technologies with some new technology to create a better warning system for pilots so that they can have proper situational awareness of their position relative to restricted airspace, and also be properly warned if they are accidentally straying into restricted airspace. Such a system must be accurate and redundant so that false alarms are not generated, and moreover human error or intentional spoofing of the system does not cause the system to fail.

SUMMARY OF THE INVENTION

In combination with a Geographic Information System (GIS), 3-dimensional shapes may be used to designate or identify blocks of airspace. These shapes may be defined in many ways including lat/long, local coordinates, or FAA transmitted directions for TFRs and ADIZs. These restricted areas and zones may be modeled using suitably modified AirScene™ software from Rannoch Corporation.

AirScene™ software can locate various aircraft in the vicinity of restricted airspace, determine whether the aircraft is about to enter restricted airspace, and issue a warning to the pilot of such aircraft that restricted airspace is about to be violated. Such a warning can be audible (e.g., radio communication message) or visual (e.g., graphic display or even a flashing light or text message) and is much less distracting than having a laser shining in the cockpit. Since the AirScene™ system is ground-based, ground personnel can also be advised if restricted airspace is being violated, or even about to be violated.

In one embodiment, a graphical representation of restricted airspace may be fed to a cockpit information display in the aircraft, such as a flat panel display, which may also display radar, mapping, and other information. For smaller General Aviation (GA) aircraft, this information may even be displayed on a handheld organizer (e.g., PalmPilot® or the like). The restricted airspace data may also be displayed or overlaid on other existing cockpit displays, including but not limited to radar displays, TCAS displays, Air Chart displays, or displays comprising any or all of these types of displays. Visual or audible warnings can be provided if breach of restricted airspace has occurred or is imminent. As in the TCAS system, a number of threat levels may be used to suitably warn the pilot of the presence of restricted airspace, the proximity of restricted airspace, and the breach of restricted airspace.

In addition to the above features, the system of the present invention may also be used to verify that altitude transponder data is indeed correct, based upon independent verification from the ground-based AirScene™ system. This aspect of the present invention may also be provided as a stand-alone feature, which may be used to calibrate, augment, or replace traditional barometric altimeters used for aircraft transponders.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the threat detection concepts of the TCAS system from a vertical perspective.

FIG. 2 is a diagram illustrating the threat detection concepts of the TCAS system from a horizontal perspective.

FIG. 3 illustrates an enhanced TCAS system display from MITRE Corporation, with other traffic and weather information.

FIG. 4 is a graphical plot of the DCA zones illustrating a sample Restricted Airspace in the Washington DC area.

FIG. 5 shows various examples of restricted areas and zones using the AirScene software.

FIG. 6 illustrates how the Gates and Profiles of the AirScene™ software may be used to mimic restricted airspace TFRs and ADIZs.

FIG. 7 illustrates one example of how warnings may be transmitted directly to a pilot.

FIG. 8 illustrates TFRs for Super Bowl XXXIX on Feb. 6, 2005.

FIG. 9 illustrates and an example of a test range for the U.S. Navy at Nanoose, near Vancouver, Canada.

FIG. 10 illustrates the two levels of Logic Showing Multiple Layers of Aircraft Protection and Alerting.

FIG. 11 is a diagram illustrating techniques employed to validate enunciated position and altitude.

FIG. 12 illustrates one embodiment of the auto warning system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 6 illustrates how the Gates and Profiles of the AirScene™ software may be used to mimic restricted airspace TFRs and ADIZs. Using this existing software, the three-dimensional profile of TFRs and ADIZs may be programmed into the system and displayed on a computer display screen or the like. Moreover, the parameters of these TFRs and ADIZs can be compared with the position and course of aircraft in the area, and a determination made whether the aircraft is heading for restricted airspace.

Using the technology of co-pending U.S. patent application Ser. No. 10/756,799, filed Jan. 14, 2004, and incorporated herein by reference, the TFR and ADIZ data can be plugged into the system in a similar matter as terrain and obstacle data. Instead of warning a pilot of an imminent collision hazard, however, the system may be programmed to warn also of possible “collision” with restricted airspace.

In addition to providing alerts to static obstacles and other aircraft the system may be used to provide pilot alerts to TFRs and ADIZs. In addition the system can be used to provide impending TFR/ADIZ busts to third parties. Thus, for example, air traffic controllers, the military and other security organizations may be alerted to a potential TFR/ADIZ “bust” and take appropriate action, including attempting to contact the pilot by radio or the like.

For general aviation aircraft and other small planes, such data may be displayed on a pilot's palm organizer, as illustrated in FIG. 7. FIG. 7 illustrates one example of how warnings may be transmitted directly to a pilot. This display, developed by Rannoch Corporation and Strategic Aeronautics, was originally designed to alert an aircraft to the presence of another aircraft. This system was successfully tested in December 2004 (see http://www.airscene.com/news2004/12_—22_—04.pdf).

For commercial aircraft and the like, such restricted airspace warnings may be displayed on an existing cockpit display, either as a selectable display, or overlaid with other data, or both. Thus, for example, the TCAS display of FIG. 3 may be suitably overlaid with restricted airspace data, such that a pilot has a greater situational awareness of their relative position to restricted airspace. Restricted airspace may also be displayed on a “heads up” or other type of display so that the pilot can view restricted airspace through the cockpit windshield, superimposed over the actual view from the cockpit.

As with terrain warnings and TCAS, audible or visual alarms may be provided if restricted airspace is about to be breached, or is actually breached. These warnings may be graduated, as with the TCAS system previously discussed, so that the pilot will initially be given a visual reference to restricted airspace in proximity to the aircraft, then given a warning if it appears the pilot is heading toward restricted airspace, and finally given a warning that restricted airspace has been breached. In these latter two cases, such warnings may be accompanied by instructions (as in TCAS) as to how to avoid or exit the restricted airspace (e.g., “turn left”). If it has been determined that a pilot has entered restricted airspace, a message may be played instructing the pilot to tune to a particular radio frequency or take other action to contact ground controllers to advise of his status, and thus avoid a possible mistaken shoot-down incident.

Note that in some instances where airspace is crowded, suitable modifications may be made to the system to prevent false alarms. For example, approaches to Reagan National Airport in Washington D.C., necessitate that aircraft approaching the airport also are approaching the restricted airspace surrounding the Capitol. As the system is ground-based, and not aircraft-based, it is a simple matter to reprogram warning parameters accordingly for each airport or zone, such that the pilot of a plane landing at National Airport is not distracted by numerous false alarms indicating the proximity of restricted airspace. The system may be programmed to indicate whether or not the pilot is on the correct approach path (and indeed, this is already a feature of the AirScene™ software) and provide restricted airspace warnings only if a significant deviation occurs from the approach path and the course heading indicated a possible breach of restricted airspace.

FIG. 12 illustrates one embodiment of the auto warning system of the present invention. In the embodiment shown in FIG. 12, the tracking and identification can make use of dependent aircraft information (such as ADS-B reported position and barometric reported altitude) 1210 as well as independently derived position (such as three-dimensional calculated position and dynamics) 1220.

Independent data 1220 may be used to validate self-reported data 1210 in step 1250. Thus, position and altitude data from aircraft signals (e.g., transponder altitude data) is correlated with independent tracking data, such as derived using multilateration (e.g., Rannoch AirScene™ system). Discrepancies between self-reported data 1210 and independent tracking data 1220 can be reported by the validation step 1250. If a serious discrepancy is noted, authorities may be alerted accordingly, as the altimeter data from the aircraft may have been intentionally altered.

The TFR/ADIZ or other restricted airspace boundaries can be either static or dynamic and may be input automatically from sources 1230 including lat/long positions and other methods. In this manner, temporary or new airspace restrictions are automatically programmed into the system. While the pilot should still brief himself on TFRs and ADIZs, the system provides a redundancy if the pilot does not receive the latest information in his briefing, or does not fully understand such a briefing or merely forgets. A geographic information system (GIS) 1240 may be used to relate aircraft, boundaries, and other geographic points of interest relative to one another.

Based on the aircraft tracking it is possible to calculate a series of aircraft alert zones 1260. For example, a series of increasing warnings that airspace boundaries may be violated in a certain time based on the dynamics of the aircraft (velocity, acceleration, climb rate etc) in a similar manner to the TCAS system or terrain avoidance systems. Combining the alert zone data 1260 with the restricted airspace data from block 1230 and 1240, the system can determine whether a warning, and what level of warning, should be sent.

Based on the anticipated boundary exceedance 1270, different levels of warnings may be sent directly to the aircraft, other aircraft 1280, or to ground based operators 1290. These warnings may be transmitted using different formats including Traffic Information Broadcast (TIS), Automatic Dependent Surveillance (ADS-B), and other methods. An automated radio signal may be sent to the pilot giving verbal instructions as to the airspace violation. Alternately, ground personnel may be alerted, and they in turn may communicate via radio with the pilot. As noted above, the data may be communicated directly to the pilot via graphical display, and/or visual or audible warning.

Furthermore, for security purposes, in addition to determining an aircraft's identity, position, and dynamics independently it is possible to use techniques to determine the aircraft's altitude independently from the aircraft's barometric altimeter—which could potentially be spoofed, intentionally or unintentionally falsified. FIG. 11 is a diagram illustrating techniques employed to validate enunciated position and altitude. This embodiment of the present invention may also be provided as a stand-alone feature, which may be used to verify, calibrate, or otherwise validate aircraft position data.

Referring to FIG. 11, aircraft 1110 may be equipped with a Secondary Surveillance radar (SSR) transponder or the like which generates a radio signal (SSR Reply) in response to an interrogation by an Air Traffic Control (ATC) radar 1130. Traditionally, these transponders output a signal identifying the aircraft by flight number, registration number, or other identifying indicia, along with altitude readout from the aircraft's altimeter. Traditional ATC radars generally cannot determine aircraft altitude, but only the aircraft's relative position (in a two dimensions) and thus rely upon the SSR reply to indicate altitude.

Barometric barometers are relatively primitive devices, which indicate relative altitude based upon air pressure. Provided the proper ground level barometric pressure is fed into the altimeter, the devices can be surprisingly accurate. However, barometric pressure changes over time, and can even change quite suddenly (with the advent of a storm front). In addition, the traditional system requires intervention in most cases of the pilot or crew to set the local barometric pressure on the altimeter, often in response to garbled verbal radio commands from ground control personnel.

If the barometric setting on the altimeter is not properly adjusted, the resultant readout can be inaccurate. As a result, air traffic controllers may not have accurate altitude information, which could result in improper routing instructions, or even a possible collision. Moreover. Inaccurate altimeter information can affect other systems, including TCAS and the like, generating false alarms or even failing to detect a possible collision. In the present invention, improper altitude indications can affect warnings for restricted airspace and the like. Moreover, a pilot intentionally trying to breach restricted airspace could reset the altimeter and/or tamper with it to make it appear as though the aircraft was not within restricted airspace (e.g., flying below or above).

In the present invention, the actual position of the aircraft in three-dimensions can be found using the multilateration techniques described in the priority applications and patents previously incorporated by reference (collectively, the AirScene™ patents). Multilateration provides an accurate three-dimensional position of the aircraft relative to the receivers 1140. Computing engine 1150, receiving the SSR reply and/or other radio signals from aircraft 1110 can determine the position of aircraft 1110 by detecting the time difference of arrival of the signals at each of receivers 1140, which may time-stamp the received signals before passing them to computing engine 1150.

Receivers 1140 may also each receive a signal from global position system (GPS) satellites 1120 (only one is shown here for the sake of illustration). From these received signals, the precise position of each receiver 1140 may be determined in computing engine 1150. Knowing the exact position (latitude and longitude, as well as altitude) of each receiver 1140, computing engine 1150 can generate an accurate aircraft position, including altitude.

This independently generated aircraft altitude position may be compared with the output of the SSR (or other) signal indicating the aircraft's altimeter reading. If the two readings are within a certain dead-band (determined by the accuracy of the aircraft altimeter with an added fudge factor) the aircraft altimeter is considered to be relatively accurate. If the aircraft altimeter reading is outside of this dead-band, a signal may be generated indicating the aircraft altimeter reading is false.

In response to such a signal, the pilot of aircraft 1110 may be notified that their altimeter is not reading properly and the pilot may take corrective actions (e.g., adjust calibration) to correct the error. Alternately, a signal may be sent electronically to the cockpit system software to automatically correct the altimeter calibration. Such a system may eliminate the need for verbally requesting barometric data and manually adjusting instruments. During the busy approach and landing phases, this is one less distracting task for the pilot to perform.

Moreover, if the altimeter reading from aircraft 1110 is so far off from the actual altitude as measured by the system, authorities may be alerted that a pilot is intentionally trying to spoof the ATC system.

While the preferred embodiment and various alternative embodiments of the invention have been disclosed and described in detail herein, it may be apparent to those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope thereof.

Claims

1. A method of providing information indicating the relative proximity of an aircraft to restricted airspace, comprising the steps of: determining position of the aircraft, determining boundaries of restricted airspace local to the aircraft position, generating at least one aircraft alert zone representing a region surrounding the aircraft, determining whether the aircraft alert zone intersects boundaries of the restricted airspace, and indicating whether an aircraft alert zone has intersected boundaries of the restricted airspace.

2. The method of claim 1, wherein the step of determining position of the aircraft comprises the steps of: receiving radio signals from the aircraft at a plurality of receiver sites, time-stamping the radio signals when received at the receiver sites, and determining aircraft position through multilateration of the time-stamped radio signals from the receiver sites.

3. The method of claim 1, wherein the step of determining position of the aircraft comprises the steps of: receiving altimeter data from the aircraft radio signals, and correlating the altimeter data from the aircraft radio signals with aircraft position determined through multilateration.

4. The method of claim 1, wherein the step of determining position of the aircraft comprises the steps of: receiving radar data from an air traffic control system indicating aircraft position, and correlating the aircraft position data from the air traffic control system with aircraft position determined through multilateration.

5. The method of claim 1, wherein the step of determining boundaries of restricted airspace local to the aircraft position further comprises the steps of: receiving restricted airspace data from a restricted airspace database, and converting the restricted airspace data into a three-dimensional model of restricted airspace for a given region of interest.

6. The method of claim 5, therein the restricted airspace data comprises at least one of Temporary Flight Restrictions (TFR) and Air Defense Identification Zones (ADIZ) data.

7. The method of claim 5, wherein the step of generating at least one aircraft alert zone representing a region surrounding the aircraft further comprises the step of: generating at least one alert zone surrounding the aircraft so as to provide one or more warning levels of impending intersection with a restricted airspace.

8. The method of claim 7, wherein the at least one aircraft alert zone corresponds to the aircraft position so as to indicate when the aircraft has entered restricted airspace.

9. The method of claim 7, wherein the step of determining whether the at least one aircraft alert zones intersects boundaries of the restricted airspace further comprises the steps of: generating a three-dimensional model of the at least one aircraft alert zones, and comparing the three-dimensional model of the at least one aircraft alert zones with the three-dimensional model of restricted airspace to determine whether any of the at least one aircraft alert zones intersect any portion of the restricted airspace.

10. The method of claim 9, wherein the step of indicating whether any of the at least one aircraft alert zones has intersected boundaries of the restricted airspace further comprises the step of: generating an alarm indicating that an aircraft alert zone has intersected the restricted airspace.

11. The method of claim 9, wherein the step of indicating whether an aircraft alert zone has intersected boundaries of the restricted airspace further comprises the step of: generating a visual display showing an aircraft alert zone and boundaries of the restricted airspace.

12. The method of claim 9, wherein the step of indicating whether an aircraft alert zone has intersected boundaries of the restricted airspace further comprises the step of: displaying on an in-cockpit display, position of the aircraft relative to boundaries of restricted airspace.

13. A system of providing information means for indicating the relative proximity of an aircraft to restricted airspace, comprising: means for determining position of the aircraft, means for determining boundaries of restricted airspace local to the aircraft position, means for generating at least one aircraft alert zone representing a region surrounding the aircraft, means for determining whether the aircraft alert zone intersects boundaries of the restricted airspace, and means for indicating whether an aircraft alert zone has intersected boundaries of the restricted airspace.

14. The system of claim 13, wherein means for determining position of the aircraft comprises: a plurality of receiver sites for receiving radio signals from the aircraft, means for time-stamping the radio signals when received at the receiver sites, and a processor for determining aircraft position through multilateration of the time-stamped radio signals from the receiver sites.

15. The system of claim 13, wherein means for determining position of the aircraft comprises: a receiver for receiving altimeter data from the aircraft radio signals, and a processor for correlating the altimeter data from the aircraft radio signals with aircraft position determined through multilateration.

16. The system of claim 13, wherein means for determining position of the aircraft comprises: an air traffic control system for indicating aircraft position, and a processor for correlating the aircraft position data from the air traffic control system with aircraft position determined through multilateration.

17. The system of claim 13, wherein means for determining boundaries of restricted airspace local to the aircraft position further comprises: a restricted airspace database for providing restricted airspace data, and a processor for converting the restricted airspace data into a three-dimensional model of restricted airspace for a given region of interest.

18. The system of claim 17, therein the restricted airspace data comprises at least one of Temporary Flight Restrictions (TFR) and Air Defense Identification Zones (ADIZ) data.

19. The system of claim 17, wherein means for generating at least one aircraft alert zone representing a region surrounding the aircraft further comprises: a processor for generating at least one alert zone surrounding the aircraft so as to provide one or more warning levels of impending intersection with a restricted airspace.

20. The system of claim 19, wherein the at least one aircraft alert zone corresponds to the aircraft position so as to indicate when the aircraft has entered restricted airspace.

21. The system of claim 19, wherein means for determining whether the at least one aircraft alert zones intersects boundaries of the restricted airspace further comprises: a processor for generating a three-dimensional model of the at least one aircraft alert zones, and a processor for comparing the three-dimensional model of the at least one aircraft alert zones with the three-dimensional model of restricted airspace to determine whether any of the at least one aircraft alert zones intersect any portion of the restricted airspace.

22. The system of claim 21, wherein means for indicating whether any of the at least one aircraft alert zones has intersected boundaries of the restricted airspace further comprises: an alarm for indicating that an aircraft alert zone has intersected the restricted airspace.

23. The system of claim 21, wherein means for indicating whether an aircraft alert zone has intersected boundaries of the restricted airspace further comprises: a visual display showing an aircraft alert zone and boundaries of the restricted airspace.

24. The system of claim 21, wherein means for indicating whether an aircraft alert zone has intersected boundaries of the restricted airspace further comprises: an in-cockpit display for displaying position of the aircraft relative to boundaries of restricted airspace.