Abstract:
A system and related methods for providing stall recovery guidance symbology via a head-up display (HUD) or similar avionics display element detects stall or near-stall conditions and provides symbology to guide the pilot through recovering from the stall by prioritizing pitch correction and disengagement of the autopilot system. Pitch correction symbology guides the pilot toward reducing the aircraft angle of attack and establishing level flight, while thrust recovery symbology helps the pilot control the application of thrust to avoid prolonging or reinstituting the stall. The system modifies the stall recovery symbology in response to detected changes in pitch, angle of attack, or airspeed. Once level flight has been established and stall conditions are no longer present, the system may transition out of stall recovery mode to regular inflight symbology.

Description:
BACKGROUND 
       [0001]    Embodiments of the inventive concepts disclosed herein are directed generally to a system for providing stall recovery guidance to an aircraft pilot or crew via responsive symbology displayed via a head-down display (HUD), a head-up display (HUD), or a head-worn display (HWD). 
         [0002]    In 2009, Air France Flight 447, an Airbus A330 out of Rio de Janeiro, crashed into the Atlantic Ocean after entering a high-altitude stall from which the aircraft never recovered. The aircraft&#39;s angle of attack (AoA) approached 40 degrees at one point and largely remained well above 30 degrees, rendering airspeed indications and stall warnings invalid. The aircraft remained in a stalled condition as it began to rapidly descend from cruising altitude, pitched upward at around 16 degrees, its engines responsive to command and continuing to develop full forward Takeoff/Go-around (TOGA) thrust until the craft struck the ocean surface. 
         [0003]    As a result of the Air France crash, FAA training regulations were revised to include stall recovery procedures, applicable broadly to aircraft of all sizes or types and generally to any stall conditions, that prioritize the reduction of AoA above achieving maximum TOGA thrust. The stall recovery procedures provide for disengaging the aircraft autopilot or autothrottle system while maintaining altitude and preventing the aircraft pitch from changing adversely (e.g., in a nose-up direction). The pilot&#39;s priority is to reduce AoA via nose-down pitch control or stabilizer trim (if necessary) while keeping the wings level (roll control). Thrust may be adjusted accordingly as needed; maximum thrust may not always be advised as the application of maximum thrust may create a nose-up pitch moment (e.g., for aircraft with engines mounted below the wing) and exacerbate a stall condition. 
         [0004]    Current HUD symbology may complement the situational awareness provided by the primary flight display (PFD) by offering recovery guidance under windshear or unusual-attitude conditions. Current symbology may indicate a stall or near stall condition to the pilot, but does not provide active guidance for stall recovery. 
       SUMMARY 
       [0005]    In one aspect, embodiments of the inventive concepts disclosed herein are directed to a system for providing stall recovery guidance symbology via an avionics display system. The system may include a head down display (HDD), head-up display (HUD), head-mounted display (HMD), head-worn display (HWD), or other avionics display element for displaying imagery. The system may include a controller coupled to the display element and to avionics systems of the aircraft. The controller may detect a stall condition of the aircraft based on data received from the avionics systems (e.g., altitude, configuration, angle of attack). The controller may detect whether the aircraft autopilot or autothrottle is active. When a stall condition is present, the controller may generate stall recovery symbology for display by the display element. The stall recovery symbology may include an annunciator of the autopilot/autothrottle status, pitch and roll correction symbology, and thrust correction symbology. 
         [0006]    In a further aspect, embodiments of the inventive concepts disclosed herein are directed to an avionics display system. The system may include a display element, such as a HDD, HUD, HMD, or HWD. The system may include a controller coupled to the display element and to avionics systems of the aircraft. The controller may detect a stall condition of the aircraft and whether the aircraft autopilot or autothrottle is currently active. While the stall condition is present, the controller may generate stall recovery guidance symbology for display by the display element, including an annunciator of the autopilot status (while the autopilot remains active), pitch/roll correction symbology, and thrust correction symbology, some or all of which may be accompanied by auditory alerts and guidance. The controller may detect changes to the aircraft pitch (angle of attack) or roll and modify the pitch/roll correction symbology accordingly. The controller may detect an airspeed change of the aircraft, and modify the thrust correction symbology accordingly. 
         [0007]    In a still further aspect, embodiments of the inventive concepts disclosed herein are directed to a method for providing stall recovery guidance symbology. The method may include detecting, via an avionics system of an aircraft, a stall condition of the aircraft. The method may include determining, via the avionics system, an active status of an autopilot or autothrottle of the aircraft. The method may include, while the autopilot or autothrottle is active, displaying an annunciator corresponding to the active status via an avionics display element. The method may include displaying, via the display element, pitch or roll correction symbology. The method may include detecting, via the avionics system, a change in the aircraft pitch or roll, and modifying the pitch or roll correction symbology accordingly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Implementations of the inventive concepts disclosed herein may be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the included drawings, which are not necessarily to scale, and in which some features may be exaggerated and some features may be omitted or may be represented schematically in the interest of clarity. Like reference numerals in the drawings may represent and refer to the same or similar element, feature, or function. In the drawings: 
           [0009]      FIG. 1  is a block diagram of the components of an exemplary embodiment of a system for stall recovery guidance according to the inventive concepts disclosed herein; 
           [0010]      FIGS. 2A through 2C  illustrate symbology displayed by the system of  FIG. 1 ; and 
           [0011]      FIGS. 3A and 3B  illustrate an exemplary embodiment of a method for providing stall recovery symbology according to the inventive concepts disclosed herein. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0012]    Before explaining at least one embodiment of the inventive concepts disclosed herein in detail, it is to be understood that the inventive concepts are not limited in their application to the details of construction and the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings. In the following detailed description of embodiments of the instant inventive concepts, numerous specific details are set forth in order to provide a more thorough understanding of the inventive concepts. However, it will be apparent to one of ordinary skill in the art having the benefit of the instant disclosure that the inventive concepts disclosed herein may be practiced without these specific details. In other instances, well-known features may not be described in detail to avoid unnecessarily complicating the instant disclosure. The inventive concepts disclosed herein are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
         [0013]    As used herein a letter following a reference numeral is intended to reference an embodiment of the feature or element that may be similar, but not necessarily identical, to a previously described element or feature bearing the same reference numeral (e.g.,  1 ,  1   a ,  1   b ). Such shorthand notations are used for purposes of convenience only, and should not be construed to limit the inventive concepts disclosed herein in any way unless expressly stated to the contrary. 
         [0014]    Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
         [0015]    In addition, use of the “a” or “an” are employed to describe elements and components of embodiments of the instant inventive concepts. This is done merely for convenience and to give a general sense of the inventive concepts, and “a’ and “an” are intended to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
         [0016]    Finally, as used herein any reference to “one embodiment,” or “some embodiments” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the inventive concepts disclosed herein. The appearances of the phrase “in some embodiments” in various places in the specification are not necessarily all referring to the same embodiment, and embodiments of the inventive concepts disclosed may include one or more of the features expressly described or inherently present herein, or any combination or sub-combination of two or more such features, along with any other features which may not necessarily be expressly described or inherently present in the instant disclosure. 
         [0017]    Broadly, embodiments of the inventive concepts disclosed herein are directed to a system and related method for providing stall recovery symbology via a head-up display (HUD) or other avionics display element. When a stall is detected, the system may help the pilot quickly and intuitively recover from the stall according to FAA stall recovery guidelines. Stall recovery symbology may prevent the pilot or crew from inadvertently exacerbating the stall in their urgency to take action. 
         [0018]    Referring to  FIG. 1 , an exemplary embodiment of a system  100  for providing stall recovery symbology according to the inventive concepts disclosed herein may include a controller  102  including one or more processors  104  and a display element  106  including a projector  108  or similar display module and a combiner  110  or similar display surface. The controller  110  may be connected to one or more aircraft sensors  112  or avionics systems  114  of an aircraft in which the system  100  is embodied. The display element  106  may be a primary flight display (PFD) or head-down display (HDD), a head-up display (HUD), a head-mounted display (HMD), or a head-worn display (HWD) configured to display fully or partially immersive imagery corresponding to the environment surrounding the aircraft. The display element  106  may include graphics processors (e.g., a synthetic vision system (SVS)) for generating explanatory symbology related to the environment and merging the symbology with the imagery to generate a combined vision stream displayed via the combiner  110 . The processors  104  of the controller  102  may generate some or all of the symbology of a combined vision stream. Based on data collected from the aircraft sensors  112  or avionics systems  114 , the controller  102  may determine that a near-stall or stall condition is present. For example, the controller  102  may be coupled to a stall warning system of the aircraft, or to external pitot tubes, vanes, or other mechanisms configured for sensing an unusual angle of attack (AoA) characteristic of a stall or near-stall condition. The controller  102  may determine that a stall or near-stall condition exists based on a combination of the AoA, the aircraft pitch, the current airspeed, or other relevant factors. 
         [0019]    Referring to  FIG. 2A , an exemplary embodiment of a system  100   a  for providing stall recovery symbology may be implemented identically to the system  100  of  FIG. 1 , except that when a stall or near-stall condition is detected by the controller  102  ( FIG. 1 ), the system  100   a  may fade out some or all of the symbology normally displayed via the combiner  110  or display surface of the system  100   a  and generate stall recovery symbology. For example, the airspeed indicator  116 , altitude indicator  118 , artificial horizon  120 , boresight symbol  122 , stall warning symbol  124 , or other relevant symbology (e.g., an AoA warning (not shown)) may be retained. 
         [0020]    Furthermore, the stall warning symbol  124  may be accompanied by an auditory alert while stall conditions persist. However, the system  100   a  may determine if the autopilot or autothrottle system of the aircraft is activated and display an autopilot annunciator  126  to provide the pilot with immediate recognition of the autopilot active status so that the autopilot system can be disabled. The autopilot annunciator  126  may include an autothrottle annunciator  126   a  indicating an active autothrottle status. The system  100   a  may terminate the autopilot annunciator  126  or autothrottle annunciator  126   a  upon determination that the autopilot or autothrottle system has been disengaged. In some embodiments, an active autopilot system may execute stall recovery procedures without direct pilot input. The system  100   a  may continue to monitor stall recovery and update the displayed stall recovery symbology accordingly, depending on detected pitch, roll or thrust changes, until stall or near-stall conditions are no longer present. 
         [0021]    During initial entry into the stall recovery symbology, the system  100   a  may generate and display a stall attitude recovery (SAR) symbol  128  indicating a target pitch attitude of the aircraft for stall recovery. When the SAR  128  is not conformal to the aircraft boresight symbol  122 , the system  100   a  may display a stall recovery chevron (SRC)  130  which rotates above the earth frame, similarly to the aircraft pitch scales  130 . The SRC  130  may indicate the desired direction of pitch correction to achieve the target pitch attitude indicated by the SAR  128 . The SAR  128  may be displayed as a ghosted (dashed) symbol when not fully within the artificial horizon  120  (e.g., when the SAR  128  is partially clipped or cropped), and may rotate or move vertically relative to the earth frame, similarly to the SRC  130 . As the pilot reduces the aircraft pitch or AoA, the presentation of the SAR  128  and SRC  130  may be modified to reflect changes in aircraft pitch or AoA by appearing closer to the boresight symbol  122 . For example, as the SAR  128  becomes fully visible within the artificial horizon  120 , the SAR may provide situational awareness of the aircraft roll orientation (in addition to that provided by the artificial horizon  120 ) so that the pilot may level the wings pursuant to stall recovery. When the SAR  128  is aligned with the boresight symbol  122 , the SRC  130  may be terminated to indicate pitch recovery, or the achievement of the target pitch attitude. 
         [0022]    Referring now to  FIG. 2B , an exemplary embodiment of a system  100   b  for providing stall recovery symbology may be implemented identically to the system  100   a  of  FIG. 2A , except that when the pilot has achieved a target pitch attitude, the SRC  130  ( FIG. 2A ) may be terminated and the SAR ( 128   a ) displayed via the combiner  110  or display surface as a solid symbol (e.g., neither ghosted nor cropped) aligned with the aircraft boresight symbol  122 . The SAR  128   a  may further indicate that the pilot has leveled the wings, and that the roll angle of the aircraft is therefore aligned with the horizontal (as indicated by the artificial horizon  120 ). Symbology displayed by the system  100   b  may include pitch guides  132  and roll guides  134  for establishing target pitch or roll zones for the pitch and roll attitudes of the aircraft (as portrayed by the SAR  128   a ). The system  100   b  may provide auditory guidance to the pilot in adjusting the pitch and roll attitudes of the aircraft to achieve the target pitch or roll zones indicated by the pitch guides  132  and roll guides  134 . The autopilot annunciator  126  may continue to be displayed (and the corresponding auditory alert may continue to sound) if the autopilot has not been disengaged. 
         [0023]    Referring to  FIG. 2C , an exemplary embodiment of a system  100   c  for providing stall recovery symbology may be implemented identically to the system  100   b  of  FIG. 2B , except that once the aircraft has achieved the target pitch attitude indicating a corrected AoA, the system  100   c  may display (via the combiner  110  ( FIG. 1 ) or display surface) a stall thrust recovery (STR) symbol  136 . The STR  136  may aid the pilot in correcting the airspeed while preventing over- or under-thrust conditions that may inhibit or counteract stall recovery. The display and modification of the STR  136  and thrust correction command may be determined algorithmically by the controller  102  ( FIG. 1 ), based on the total lift equation 
         [0000]    
       
         
           
             L 
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                 C 
                 L 
               
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               ρ 
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                   V 
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                 2 
               
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               S 
             
           
         
       
     
         [0000]    (for lift L, lift coefficient C L  air density ρ, velocity V, and wing surface area S). The controller  102  may determine that the aircraft has achieved stable flight, e.g., that near-stall or stall conditions no longer exist. Accordingly, visible and auditory stall warnings (e.g., the stall warning symbol  124  ( FIG. 2A ) and corresponding alert) may be terminated by the controller  102 . The system  100   c  may transition into the normal symbology displayed via the combiner  110  or display surface, e.g., by blending the SAR  128   a  into the flight path symbol  138 , so the pilot does not have to scan the display surface to locate the flight path symbol. The STR  136  may be accompanied by a target airspeed guide  140 , indicating a target airspeed toward which the pilot may adjust, as well as auditory guidance in adjusting airspeed to achieve the target airspeed. 
         [0024]    Stall recovery symbology may be displayed via the combiner  110  or display surface as monochrome or colored symbols, depending on, e.g., whether the display element  106  ( FIG. 1 ) is a PFD/HDD, HUD, HMD, or HWD. Stall recovery symbology may be further modified according to human factors considerations. For example, the stall recovery symbology may be implemented as flashing symbols, or more boldly than the airspeed indicator  116  or altitude indicator  118  to appear brighter or to be more easily identified and instantly interpreted by the pilot. 
         [0025]    Referring now to  FIG. 3A , an exemplary embodiment of a method  200  for providing stall recovery symbology according to the inventive concepts disclosed herein may be implemented by the system  100  in some embodiments, and may include one or more of the following steps. At a step  202 , the controller of the display element (HDD, HUD, HMD, HWD) detects a near-stall or stall condition of the aircraft. For example, the controller may determine a stall based on the aircraft angle of attack (AoA) or based on the aircraft configuration (e.g., the detected state of aircraft flaps, gear, or other internal and external components). The controller may be coupled to a stall warning system, which may be used as a basis for determining stall or near-stall conditions. 
         [0026]    At a step  204 , the controller determines whether the aircraft autopilot or autothrottle system is active. 
         [0027]    At a step  206 , the display element displays a stall warning symbol. The stall warning may include auditory alerts or warnings generated by the display element. 
         [0028]    At a step  208 , the display element displays an annunciator corresponding to the active status of the autopilot or autothrottle. 
         [0029]    At a step  210 , the display element displays pitch correction and roll correction symbols. For example, the display element may display a SAR corresponding to a target pitch attitude associated with stall recovery, and a SRC indicating the desired direction of pitch correction for achieving the target pitch attitude. The SAR may indicate the target roll attitude as well as the target pitch attitude. The display element may display additional symbology to guide the pilot toward the target pitch and roll attitudes. The displayed symbology may be accompanied by auditory alerts. 
         [0030]    At a step  212 , the controller detects a change in the aircraft pitch attitude (AoA) or a change in the aircraft roll attitude. 
         [0031]    At a step  214 , the controller modifies the pitch correction symbology or the roll correction symbology displayed by the display element in response to the detected change in pitch attitude/AoA or the detected change in roll attitude. For example, the controller may remove the SRC if the aircraft has achieved level flight, and display stall thrust recovery symbology to provide the pilot with thrust correction guidance. 
         [0032]    Referring now to  FIG. 3B , the method  200  may include additional steps  216  and  218 . At the step  216 , the controller detects a change in airspeed or thrust of the aircraft. 
         [0033]    At the step  218 , the controller modifies the thrust correction symbology displayed by the display element in response to the detected change in airspeed or thrust. 
         [0034]    As will be appreciated from the above, systems and methods according to embodiments of the inventive concepts disclosed herein may provide enhanced situational awareness and simplified guidance for quickly and efficiently taking steps to recover aircraft of all sizes and configurations from stall or near-stall conditions. Stall recovery symbology may provide pilots with clear guidance through the stall recovery process, reducing the possibility that the urgency of a stall condition may inadvertently lead to counterproductive actions. 
         [0035]    It is to be understood that embodiments of the methods according to the inventive concepts disclosed herein may include one or more of the steps described herein. Further, such steps may be carried out in any desired order and two or more of the steps may be carried out simultaneously with one another. Two or more of the steps disclosed herein may be combined in a single step, and in some embodiments, one or more of the steps may be carried out as two or more sub-steps. Further, other steps or sub-steps may be carried out in addition to, or as substitutes to one or more of the steps disclosed herein. 
         [0036]    From the above description, it is clear that the inventive concepts disclosed herein are well adapted to carry out the objectives and to attain the advantages mentioned herein as well as those inherent in the inventive concepts disclosed herein. While presently preferred embodiments of the inventive concepts disclosed herein have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the broad scope and coverage of the inventive concepts disclosed and claimed herein.