Aircraft traffic alert and collision avoidance system with autoflight system mode protection

TECHNICAL FIELD

0001The present disclosure generally relates to aircraft traffic alert and collision avoidance system (TCAS) technologies. More particularly, the present disclosure relates to autoflight system mode protection for automated TCAS recovery maneuvers.

BACKGROUND

0002Since its introduction more than two decades ago, the traffic alert and collision avoidance system (TCAS) has provided tremendous safety advantages by reducing the risk of mid-air collisions. By interrogating the transponders of surrounding aircraft, TCAS analyzes the replies from these transponders to determine the range, bearing, and relative altitude (if reporting altitude) of each surrounding aircraft ("intruder"). TCAS provides a display for traffic awareness, and both aural and visual alerts are issued when a possible mid-air collision hazard becomes imminent. TCAS generally issues two levels of advisories. A traffic advisory (TA) is a caution level alert to inform the crew that closing traffic is in the vicinity of the crew's aircraft ("ownship"). If the intruder continues to close, TCAS issues a warning level resolution advisory (RA) that provides guidance to assure safe vertical separation.

0003Resolution advisories may further be categorized into two response types. A preventive RA requires the pilot to avoid certain deviations from the current vertical speed (<i>e.g</i>., "Monitor Vertical Speed", RA requiring the pilot not to climb or descend while in level flight). A Preventive RA does not require the pilot to alter the airplane's existing flight path. A corrective RA requires the pilot to either deviate from current vertical speed (such as "Climb" RA while in level flight), or to maintain an existing climb or descent rate. TCAS provides a vertical speed target for the ownship to maneuver to or maintain in order to provide separation from the intruder.

0004TCAS bases the alerts on an assumed five-second crew reaction time to achieve adequate separation. A traffic display presents the location of intruder traffic. Compliance with a TCAS RA is mandatory unless the pilot considers it unsafe to do so, or if the pilot has better information about the cause of the RA and can maintain safe separation (<i>e.g</i>., visual acquisition of, and safe separation from, a nearby airplane, obvious TCAS system failure, etc.) The RA display is incorporated into the vertical speed indicator (VSI) or the primary flight display (PFD)/attitude direction indicator (ADI). Green and red zones are presented on the VSI or ADI (pitch ladder) which depict fly-to and avoidance zones, respectively. These are consistent with the required vertical rate or pitch attitude, or limitation of climb or descent, issued by TCAS to avoid a possible collision.

0005Operational experience shows that pilot response to a TCAS RA is at times incorrect or contrary to TCAS commands, for example the initial pilot response may be too slow, or may not be as aggressive as assumed, or may be in the wrong direction. It is also known that improper maneuvers may lead to excessive altitude gain/loss and incursion of adjacent flight levels. In order to alleviate these problems known in the art, various autopilot-coupled TCAS systems are currently under development and testing, which enable the autopilot to automatically fly TCAS RA maneuvers per the existing TCAS functionality. Upon full implementation, AP TCAS is expected to significantly reduce incorrect RA responses, resulting in an overall increase in safety.

0006As noted above, during a Preventive RA, the flight crew is not required to change the aircraft's flight path. Thus, safe separation from an intruder is assured on the current flight path. However, separation will be compromised if the aircraft is maneuvered into the "no fly" vertical speed area depicted on the VST. Hence, the AP TCAS system does not maneuver the aircraft during Preventive RAs. However, a problem may arise when the aircraft's flight management system (FMS) is programmed with a vertical navigation (VNAV) path or other pitch mode manually selected on the mode control panel (MCP), and this path or mode is continued to be followed during a preventive RA, if the vertical speeds commanded approach the TCAS protected limits.

0007Accordingly, there remains a need in the art for improved TCAS systems, especially those that are coupled with an aircraft's autopilots systems. The improved TCAS systems would limit the autopilot from commanding vertical speeds contrary to TCAS commands during a preventive RA, and/or initiate an AP TCAS maneuver if the current vertical speed is nearing (or exceeds) the protected TCAS vertical speed limit. Both of these solutions would provide additional protection prior to any onset of the conventional corrective RA and minimize unnecessary maneuvering. Furthermore, other desirable features and characteristics of the disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

0008<patcit id="pcit0001" dnum="US20080021647A"><text>US2008/0021647 (AIRBUS FRANCE), published 24-01-2008</text></patcit>, discloses an avoidance method and system for an aircraft, said avoidance system comprising an anti-collision system, calculation means for automatic determination of avoidance instructions, when an automatic pilot is engaged, from avoidance information received from the anti-collision system and an avoidance aid system, connected to the calculation means which aid the piloting of the aircraft, by means of the instructions received from said calculation means.

BRIEF SUMMARY

0009The present disclosure relates to autopilot-coupled traffic alert and collision avoidance systems (AP TCAS). The invention is defined by independent claims 1 and 8. In one example not covered by the scope of the claims, an AP TCAS includes a flight management system (FMS) that is configured to provide a first and a second aircraft vertical speed setting; an autopilot (AP)/automatic flight control system (AFCS) system that is configured to automatically cause the aircraft to fly at a vertical speed in accordance with the first vertical speed setting; a traffic alert and collision avoidance system (TCAS) that senses a range, bearing, and relative altitude of an intruder aircraft, and, based on the sensed range, bearing, and relative altitude, is configured to issue a preventative resolution advisory (RA) that indicates a maximum vertical speed the aircraft should not exceed in order to avoid a conflict with the intruder aircraft; and an AP/AFCS that is configured to receive the second aircraft vertical speed setting after the TCAS issues the preventive RA, wherein the second aircraft vertical speed setting exceeds the maximum vertical speed, the AP/AFCS being further configured to: (1) modify the second aircraft vertical speed setting so as to be less than the maximum vertical speed, and relay the modified second aircraft vertical speed to the AP/AFCS system to automatically cause the aircraft to fly at a vertical speed in accordance with the modified second vertical speed setting; and (2) relay a command to the AP/AFCS system to initiate an automatic, corrective flight maneuver if a current vertical speed of the aircraft is within a predetermined threshold or amount of the maximum vertical speed or exceeds the maximum vertical speed.

0010This brief summary is provided to describe select concepts in a simplified form that are further described in the Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

0011The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a block diagram of a flight system suitable for use in an aircraft in accordance with an aspect not covered by the scope of the claims;</li><li><figref idref="f0002">FIG. 2</figref> is a block diagram of an autopilot coupled TCAS implemented in accordance with the embodiment described herein; and</li><li><figref idref="f0002">FIG. 3</figref> is a diagram illustrating an example of the operation of the autopilot coupled TCAS of <figref idref="f0002">FIG. 2</figref></li></ul>

DETAILED DESCRIPTION

0012The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word "exemplary" means "serving as an example, instance, or illustration." All of the embodiments described herein are provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.

0013Techniques and technologies may be described herein in terms of functional and/or logical block components, and with reference to symbolic representations of operations, processing tasks, and functions that may be performed by various computing components or devices. Such operations, tasks, and functions are sometimes referred to as being computer-executed, computerized, software-implemented, or computer-implemented. In practice, one or more processor devices can carry out the described operations, tasks, and functions by manipulating electrical signals representing data bits at memory locations in the system memory, as well as other processing of signals. The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to the data bits. It should be appreciated that the various block components shown in the figures may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, a system or a component may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices.

0014For the sake of brevity, conventional techniques related to graphics and image processing, navigation, flight planning, aircraft controls, aircraft data communication systems, and other functional aspects of certain systems and subsystems (and the individual operating components thereof) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements.

0015The following description refers to elements or nodes or features being "coupled" together, in particular the AP TCAS. As used herein, unless expressly stated otherwise, "coupled" means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically. In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting.

0016Technologies and concepts discussed herein relate to improvements for autopilot coupled traffic alert and collision avoidance systems. The disclosed improvements limit the AP from commanding vertical speeds contrary to TCAS commands during a preventive RA, and/or initiate an AP TCAS maneuver if the current vertical speed is nearing (or exceeds) the protected TCAS vertical speed limit. The autopilot is a system integrated with the aircraft controls. Track/Heading and altitude commands are sent to the autopilot that controls the aircraft by engaging corresponding functionality of the automatic flight control system (AFCS), e.g., Level Change (LVL CHG) for descent, Altitude Hold (ALT HLD) to maintain selected altitude, and Heading or Track hold (HDG/TRK) to maintain selected heading or track. The autopilot systems and algorithms described herein cooperates with other on board equipment, in particular TCAS as noted above, and additionally, for example, weather radar, enhanced ground proximity warning system (EGPWS), and flight management system (FMS).

0017Referring to <figref idref="f0001">FIG. 1</figref>, an exemplary flight deck navigation system 100 is depicted and will be described for implementing an aspect not covered by the scope of the claims of the present disclosure. The system 100 includes a user interface 102, a navigation computer 104 (for example, an FMS), a processor 106, one or more navigation databases 108, one or more terrain databases 109, various optional sensors 112, various external data sources 114, and a display device 116. In an aspect the user interface 102 and the display device 116 may be combined in the same device, for example, a touch pad. The user interface 102 is in operable communication with the FMS 104 and the processor 106 and is configured to receive input from a user 101 (e.g., a pilot) and, in response to the user input, supply command signals to the FMS 104 and the processor 106. The user interface 102 may be any one, or combination, of various known user interface devices including, but not limited to, a cursor control device (not shown), such as a mouse, a trackball, or joystick, and/or a keyboard, one or more buttons, switches, or knobs.

0018The FMS 104 may include one of numerous known general-purpose microprocessors 103 or an application specific processor that operates in response to program instructions. In the depicted aspect, the FMS 104 includes on-board memory 105. The program instructions that control the processor 103 may be stored in the memory 105. It will be appreciated that this is merely exemplary of one scheme for storing operating system software and software routines, and that various other storage schemes may be implemented. It will also be appreciated that the processor 104 may be implemented using various other circuits, not just a programmable processor. For example, digital logic circuits and analog signal processing circuits could also be used.

0019The processor 106 operates to monitor and direct the navigation of the aircraft, and is coupled to the FMS 104, GPS receiver 122 and the other avionics receivers 118. The processor includes memory (107) for storing instructions (software) and data from the FMS 104, GPS receiver 122, and other avionics receivers 118.

0020The memory 105, 107 may be realized as RAM memory, flash memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art, in particular non-transitory storage means. In this regard, the memory 105, 107 can be coupled to the processor 103, 106, respectively, such that the processors 103, 106 can be read information from, and write information to, the memory 105, 107. In the alternative, the memory 105 may be integral to the processor 103, and the memory 107 may be integral to the processor 106. As an example, the processor 106 and the memory 107 may reside in an ASIC. In practice, a functional or logical module/component of the navigation system 100 might be realized using program code that is maintained in the memory 107.

0021The processors 103, 106 may be implemented or realized with a general purpose processor, a content addressable memory, a digital signal processor, an application specific integrated circuit, a field programmable gate array, any suitable programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination designed to perform the functions described herein. A processor device may be realized as a microprocessor, a controller, a microcontroller, or a state machine. Moreover, a processor device may be implemented as a combination of computing devices, e.g., a combination of a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a digital signal processor core, or any other such configuration.

0022No matter how the processor 103 is specifically implemented, it is in operable communication with the processor 106, the navigation databases 108, autopilot system, and the display device 116, and is coupled to receive various types of aircraft state data from the various sensors 112, and various other environment related data from the external data sources 114. The processor 103 is configured, in response to the inertial data and the avionics-related data, to selectively retrieve navigation data from one or more of the navigation databases 108, and to supply appropriate display commands to the display device 116. The display device 116, in response to the display commands from, for example, a touch screen, keypad, cursor control, line select, concentric knobs, voice control, and data link message, selectively renders various types of textual, graphic, and/or iconic information.

0023The terrain databases 109 include various types of data representative of the terrain over which the aircraft is flying, and the navigation databases 108 include various types of navigation-related data. These navigation-related data include various flight plan related data such as, for example, waypoints, distances between waypoints, headings between waypoints, data related to different airports, navigational aids, obstructions, special use airspace, political boundaries, communication frequencies, and aircraft approach information. It will be appreciated that, although the terrain databases 109 and the navigation databases 108 are, for clarity and convenience, shown as being stored separate from the processor 104, all or portions of either or both of these databases 109, 108 could be loaded into the memory 105, or integrally formed as part of the processor 104. The terrain/taxiway databases 109 and navigation databases 108 could also be part of a device or system that is physically separate from the system 100.

0024The navigation databases 108 include various types of navigation-related data. These navigation-related data include various flight plan related data such as, for example, waypoints, distances between waypoints, headings between waypoints, data related to different airports, navigational aids, obstructions, special use airspace, political boundaries, communication frequencies, and aircraft approach information. It will be appreciated that, although the navigation databases 108 are, for clarity and convenience, shown as being stored separate from the FMS 104, all or portions of either or both of these databases 108 could be loaded into the memory 105, or integrally formed as part of the processor 103, and/or memory 105. The navigation databases 108 could also be part of a device or system that is physically separate from the system 100.

0025The sensors 112 may be implemented using various types of sensors, systems, and or subsystems, now known or developed in the future, for supplying various types of aircraft state data. The state data may also vary, but preferably include data representative of the geographic position of the aircraft and also other data such as, for example, aircraft speed, heading, altitude, and attitude.

0026The number and type of external data sources 114 (or subsystems) may also vary, but typically include for example, a GPS receiver 122, other avionics receivers 118 including, for example, a VOR/ILS, and a data link unit 119. The other avionics receivers would include, for example, a terrain avoidance and warning system (TAWS), a traffic alert and collision avoidance system (TCAS), a flight director, and a navigation computer.

0027The display device 116, as noted above, in response to display commands supplied from the processor 104, selectively renders various textual, graphic, and/or iconic information, and thereby supply visual feedback to the user 101. It will be appreciated that the display device 116 may be implemented using any one of numerous known display devices suitable for rendering textual, graphic, and/or iconic information in a format viewable by the user 101. Non-limiting examples of such display devices include various cathode ray tube (CRT) displays, and various flat panel displays such as various types of LCD (liquid crystal display) and TFT (thin film transistor) displays. The display device 116 may additionally be implemented as a panel mounted display, a HUD (head-up display) projection, or any one of numerous known technologies. It is additionally noted that the display device 116 may be configured as any one of numerous types of aircraft flight deck displays. For example, it may be configured as a multi-function display, a horizontal situation indicator, or a vertical situation indicator, just to name a few. In an embodiment, the display device 116 is configured as a primary flight display (PFD).

0028Onboard data link 119 is coupled to an external data link 120 and is configured to transmit and receive data from ground stations and other aircraft. Examples of the data received include, for example, weather information, traffic information, route changes, and clearances and alerts (including NOTAMS). In accordance with the present exemplary embodiments, the onboard data link unit 119 transmits a messages related to the emergency descent.

0029It should be understood that <figref idref="f0001">FIG. 1</figref> is a simplified representation of a system 100 for purposes of explanation and ease of description, and <figref idref="f0001">FIG. 1</figref> is not intended to limit the application or scope of the subject matter in any way. In practice, the system 100 will include numerous other devices and components for providing additional functions and features, as will be appreciated in the art.

0030With particular attention now to the above-noted autopilot-coupled TCAS, <figref idref="f0002">FIG. 2</figref> presents a schematic illustration of one possible implementation of an AP TCAS 200 suitable for use in accordance with the present disclosure. AP TCAS includes the above-described input controls 102, FMS 104, other avionics receivers (including TCAS) 118, and display 116. These elements are coupled with an automatic flight control system (AFCS) 210, which in turn is coupled with autopilot/autothrottle 220. Many implementations of AFCS 210 and autopilot/autothrottle are known in the art, and thus disclosure should not be understood as limited to any particular configuration or implementation thereof.

0031As mentioned above, the AP TCAS 200 functions only performs automatic evasive maneuvers in response to TCAS RAs - there is no system response to a TA and pilot monitoring task remains unchanged. The RA recovery guidance provided by TCAS 118 does not change from conventional design and is still based on vertical speed.

0032Preventive RA's do not require pilot action hence the AP Coupled TCAS 200 will not maneuver the aircraft. The pilot is presented with conventional TCAS aural and visual traffic awareness and alerting. However, the AP TCAS system enters an "armed" state. For a Corrective RA, the system 200 engages with vertical speed target set to "fly out of the red zone/into the green zone". All previously armed pitch modes are cancelled. A "TCAS" flight mode annunciation (FMA) presented on the PFD 116 indicates the new active mode. The flight crew monitors the maneuver by scanning the VSI and PFD RA cues. The AP 220 follows the TCAS RA until "Clear of Conflict" condition or other indication of end of maneuver. The pilot maneuvers back to the original clearance or as per ATC instructions.

0033<figref idref="f0002">Figure 3</figref> presents an example of the AP TCAS 200 operation. Items 1 through 10 are described in <figref idref="f0002">FIG. 3</figref> as follows: <ol id="ol0001"><li>1) In this example the AP is engaged in altitude hold ALT;</li><li>2) TCAS generates a TA;</li><li>3) FMA annunciates "TCAS" as armed;</li><li>4) There is no AP TCAS response for a TA, the flight crew is required to monitor traffic;</li><li>5) The TCAS generates a Climb Corrective RA;</li><li>6) "TCAS" annunciation is provided on the FMA;</li><li>7) The AP switches from altitude hold to TCAS mode, the aircraft climbs to avoid the red area/attain the green area of VSI (vertical speed indicator);</li><li>8) Airplane levels off at "Level Off' indication (Note - aural is "Adjust Vertical Speed" in TCAS versions prior to 7.1);</li><li>9) AP follows TCAS RAs until "Clear of Conflict" or other indication of end of maneuver; and</li><li>10) TCAS FMA annunciation is cleared.</li></ol>

0034As initially noted above, during a preventive RA the flight crew is not required to change the flight path of the aircraft. In this case, TCAS 118 has determined that safe separation from an intruder will be compromised if aircraft is maneuvered into the "no fly" vertical speed area depicted on the VSI (or red zone on the PFD pitch scale). Hence, the AP TCAS 200 does not maneuver the aircraft. It is currently permissible that the FMS 104 programmed VNAV path or other pitch mode manually selected on the mode control panel (MCP) would continue to be followed during a preventive RA. For example, consider the case where an aircraft is coupled to the FMS VNAV path and TCAS issues a vertical speed limit RA (<i>e.g.,</i> "Do Not Descend >1000 fpm"). The FMS VNAV path could include a leg with a vertical descent potentially resulting in a maneuver contrary to the TCAS vertical speed limit (<i>e.g</i>., descending very close to or into the restricted avoidance zone). However, note for any flight into the TCAS protected zone, it is expected that the RA would change from a preventive to corrective RA requiring pilot action.

0035In the embodiment, the present disclosure thus provides two improvements to the design above: (a) limit the AP from commanding vertical speed maneuvers contrary to TCAS commands during a Preventive RA; and/or (b) initiate an AP TCAS maneuver if the current vertical speed is nearing (or exceeds) the protected TCAS vertical speed limit. Both of these solutions provide additional protection prior to any onset of the conventional corrective RA.

0036This disclosed solution requires the addition of a monitor to the flight control system. This monitor would detect if a vertical speed limit is being commanded by TCAS. For (a) above, protection is provided by limiting any vertical mode from commanding vertical speeds in excess of the TCAS protected limit. For example, if TCAS issues a limit to vertical speed commands (<i>e.g</i>., "Do Not Descend > 1000 fpm"), and the FMS commands a descent at 1500 fpm, the flight monitor will detect this condition and place a limit on the FMS commanded vertical speed. The aircraft retains the FMS mode, but will limit the descent to 1000 fpm per TCAS issued vertical speed limit.

0037In the embodiment ((b) above), the current vertical mode would be restricted in maneuvering the aircraft either close to, or within, the protected TCAS vertical speed limit. The AP TCAS initiates recovery if the TCAS protected vertical speed limit is encroached. A viable solution is to enter an "armed" TCAS mode for a preventive RA, and enter an "active" AP TCAS mode should the aircraft enter a pre-determined threshold from the protected vertical speed limit (for example 250 fpm). Upon termination of the RA, the system will dismiss the armed TCAS mode (if it did not engage) or performs a normal end of maneuver transition.

0038In the embodiment, note also that although vertical mode protection is described above, the concept can also be applied to lateral mode protection (<i>e.g.</i>, TCAS III). For example, in an alternative embodiment, the system may provide inadvertent AFCS lateral maneuver guidance protection in the case where the AP TCAS also engages lateral maneuvering of the aircraft. The intent is to prevent the AFCS from issuing commands contrary to lateral guidance provided by TCAS. Consider the case, where an advanced traffic collision avoidance system issues a "maintain heading" (lateral) command. In this case, the current aircraft heading should be maintained to prevent conflict with laterally off-set traffic. It is conceivable that when arriving at an FMS waypoint while in LNAV mode, the AFCS may automatically issue a heading change compliant with the next FMS leg. This turning command would be contrary to the "maintain heading" collision avoidance guidance. Similarly, the pilot could manually set a new erroneous heading on the guidance control panel. In this embodiment, the system would detect the lateral conflict with traffic and limit the AFCS commanded heading change. This would prevent the AFCS system from initiating the turn maneuver into the protected avoidance zone.

0039In the embodiment, the system may provide AFCS protection in combination in both lateral and vertical modes. This would ensure that the AFCS commands would be limited in both lateral and vertical modes to ensure that the aircraft maneuvering is limited to the protected zone.