Abstract:
A method and system for determining a deviation of a vehicle from a desired course are described. The method includes receiving bearing signals from a transmitter, accessing a database, on the vehicle, to obtain transmitter position information identifying a position of the transmitter, obtaining vehicle position information using GPS identifying a current position of the vehicle, and determining a deviation of the vehicle from the desired course utilizing the transmitter position information, the vehicle position information, and the bearing signal. The system includes a receiver receiving a bearing signal from a transmitter, a database storing transmitter position information identifying a position of the transmitter, a GPS receiver obtaining vehicle position information identifying a current position of the vehicle based on a GPS signal, and a controller determining a deviation of the vehicle from the desired course utilizing the transmitter position information, the vehicle position information, and the bearing signal.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to aircraft navigation and landing. More specifically, embodiments of the invention relate to methods and systems for navigating and landing aircraft. 
     A VHF (very high frequency) Omni-directional Range (VOR) navigation system is implemented by dispersing VOR transmitter facilities across a geographic area. VOR receivers are located on aircraft which navigate through such a geographic area. The basic principle of operation of the VOR navigation system includes transmission from the VOR transmitter facilities transmitting two signals at the same time. One VOR signal is transmitted constantly in all directions, while the other is rotatably transmitted about the VOR transmission facility. The airborne VOR receiver receives both signals, analyzes a phase difference between the two signals, and interprets the result as a radial to or from the VOR transmitter  100 . The VOR navigation system allows a pilot to simply, accurately, and without ambiguity navigate from VOR transmitter facility to VOR transmitter facility. Each VOR transmission facility operates at frequencies that are different from surrounding VOR transmitters. Therefore a pilot can tune their VOR receiver to the VOR transmission facility to which they wish to navigate. Widely introduced in the 1950s, VOR remains one of the primary navigation systems used in aircraft navigation. 
     The rotating transmission signal is achieved through use of a phased array antenna at the VOR transmission facility. Separation between elements of the array causes nulls in the signal received at the aircraft. Element separation may also cause erratic signal reception when an aircraft is within an area above the antenna array. Such nulls result in a conically shaped area originated at the VOR transmitter and extending upward and outward at a known angle. The conically shaped area is sometimes referred to as a cone of confusion. When an aircraft is within the cone of confusion, a pilot typically navigates utilizing only heading information, a process sometimes referred to as dead-reckoning. It is advantageous for a pilot to know that he or she is entering the cone of confusion. 
     An instrument landing system (ILS) also includes ground based transmitters, located at runways, and airborne receivers. The ILS transmitters transmit signals, received by the receivers on the aircraft, which are utilized to align an aircraft&#39;s approach to a runway. Typically, an ILS consists of two portions, a localizer portion and a glide slope portion. The localizer portion is utilized to provide lateral guidance and includes a localizer transmitter located at the far end of the runway. The glide slope portionprovides vertical guidance to a runway and includes a glide slope transmitter located at the approach end of the runway. More specifically, a localizer signal provides azimuth, or lateral, deviation information which is utilized in guiding the aircraft to the centerline of the runway. The localizer signal is similar to a VOR signal except that it provides radial information for only a single course, the runway heading. The localizer signal includes two modulated signals, and a null between the two signals is along the centerline path to the runway. 
     The glide slope provides vertical guidance to the aircraft during the ILS approach. The glide slope includes two modulated signals, with a null between the two signals being oriented along the glide path angle to the runway. If the aircraft is properly aligned with the glide slope signal, the aircraft should land in a touchdown area of the runway. A standard glide slope or glide path angle is three degrees from horizontal, downhill, to the approach-end of the runway. Known flight guidance systems, sometimes referred to as flight control systems, are configured to assume a nominal glide path angle, for example, three degrees. Some known flight guidance systems have difficulty capturing the null in the glide slope signal at runways whose glide path angle varies significantly from the assumed glide path angle. 
     The VOR, localizer, and glide slope all provide an angular deviation from a desired flight path. The angular deviation is the angle between the current flight path and the desired flight path. Depending on a distance from a transmitter, a linear change to the flight path to correct an angular deviation can vary widely. A linear deviation is the current distance between the current flight path and the desired flight path. Furthermore, most flight guidance systems are better suited to receive and process linear deviations from a desired flight path. Known flight guidance systems utilize data from distance measuring equipment (DME) and radar altimeters to convert angular deviations in one or more of VOR, localizer, and glide slope, into linear deviations that can be acted upon by a pilot or a flight guidance system. Therefore, aircraft not equipped with DME or a radar altimeter are not able to convert the angular deviations into linear deviations that can be optimally acted upon by the flight guidance system. 
     Known flight guidance systems utilize distance information from DME to estimate a distance to a VOR transmitter. The estimated distance, along with an angular deviation as determined from the VOR bearing is utilized to determine a linear deviation from a desired flight path and detect a cone of confusion. However, this approach assumes a default VOR transmitter station elevation, that the aircraft is equipped with DME, and that a DME station is co-located with the VOR transmitter. 
     Known flight guidance systems also utilize altitude information from, for example, a radar altimeter to estimate localizer deviations. The altitude, along with an angular deviation as determined by the localizer receiver is utilized along with an assumption of runway length to determine a localizer linear deviation from a desired flight path. For glide slope linear deviations, the altitude, an angular deviation as determined by a glide slope receiver, and an assumed glide path angle are utilized to estimate the linear deviation from a desired glide slope. These estimations assume that the aircraft is equipped with an altitude measuring device (e.g. radar altimeter). It would be advantageous to utilize actual data relating to VOR, localizers, glide slopes, and runway lengths and altitudes when providing a pilot or an auto pilot system navigation data. Similarly, it would be advantageous to provide such navigation data in aircraft which are not equipped with radar altimeters or DME. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment of the present invention, a method for determining the deviation of a vehicle from a desired course is provided. The method comprises receiving bearing signals from a transmitter, accessing a database, on the vehicle, to obtain transmitter position information identifying, a position of the transmitter, obtaining vehicle position information using GPS identifying a current position of the vehicle, and determining a deviation of the vehicle from the desired course utilizing the transmitter position information, the vehicle position information, and the bearing signal. 
     In another embodiment of the present invention, a system for determining a deviation of a vehicle from a desired course is provided. The system comprises a receiver receiving a bearing signal from a transmitter, a database storing transmitter position information identifying a position of the transmitter, a GPS receiver obtaining vehicle position information identifying a current position of the vehicle based on a GPS signal, and a controller determining a deviation of the vehicle from the desired course utilizing the transmitter position information, the vehicle position information, and the bearing signal. 
     In still another embodiment of the present invention, a flight control system is provided that comprises a database and a flight director. The data from the database is available to the flight director, and pitch and roll commands initiating from the flight director are based at least partially on the data within the database. 
     In yet another embodiment of the present invention, a computer program product embodied on a computer readable medium for determining a deviation of a vehicle from a desired course is provided which comprises a data reception source code segment, a database access source code segment, and a determination source code segment. The data reception source code segment receives data relating to an angular deviation of the vehicle as determined from bearing signals received from a transmitter, and data relating to a position of the vehicle. The database access source code segment retrieves data from a database relating to a position of the transmitter supplying the bearing signals. The determination source code segment determines a linear deviation from a desired path utilizing the data relating to angular deviation, the data relating to transmitter position, and the data relating to vehicle position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the invention noted above are explained in more detail with reference to the drawings which form a part of the specification and which are to be read in conjunction therewith, and in which like reference numerals denote like elements in the various views. 
         FIG. 1  is a block diagram of a portion of a flight guidance system according to one embodiment of the present invention. 
         FIG. 2  is a diagram illustrating a number of parameters utilized in calculating a linear deviation from a desired path to a VOR transmitter. 
         FIG. 3  is a diagram illustrating a number of parameters utilized in estimating a cone of confusion above a VOR transmitter. 
         FIG. 4  is a diagram illustrating a number of parameters utilized in calculating a linear deviation from a desired path to a localizer transmitter. 
         FIG. 5  is a diagram illustrating a number of parameters utilized in calculating a linear deviation from a desired back course path to a localizer transmitter. 
         FIG. 6  is a diagram illustrating a number of parameters utilized in calculating a linear deviation from a desired path to a glide slope transmitter. 
         FIG. 7  is a flowchart describing a method for determining a linear deviation from a desired path to a VOR transmitter. 
         FIG. 8  is a flowchart describing a method for determining a linear deviation from a desired path to a localizer transmitter. 
         FIG. 9  is a flowchart describing a method for determining a linear deviation from a desired glide slope angle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a block diagram of a portion of a flight guidance system  10  according to one embodiment of the present invention. The flight guidance system  10 , typically including a flight director and autopilot function, includes a microprocessor  12  that is coupled to each of a program memory  14 , a database  16 , pilot controls  18 , and a pilot display  20 . In the embodiment shown, the flight guidance system  10  receives aircraft position data from GPS receiver  30 , which is connected to GPS antenna  32 . The flight guidance system  10  also receives inputs from a VHF Omni-directional Range (VOR) receiver  40 , which is connected to VOR antenna  42 . As described above, the VOR system is utilized to navigate from VOR transmitter to VOR transmitter along a planned flight path. VOR transmitters are interspersed across a geographic area to provide navigation references for aircraft equipped with VOR receivers  40 . 
     Once an aircraft has navigated past the last VOR transmitter in the planned flight path, it will begin an approach to an airport, and may begin to receive signals from an instrument landing system (ILS). As the air vehicle (not shown in  FIG. 1 ) in which the flight guidance system  10  is installed approaches the runway for landing, it will receive input data from the ILS. An ILS may include a localizer receiver  50 , localizer antenna  52 , a glide slope receiver  60 , and a glide slope antenna  62 . The flight guidance system  10  also receives altitude data  70  from an altitude source, for example, an altimeter corrected for barometric pressure (not shown). 
     The localizer receiver  50 , and the glide slope receiver  60  receive signals from corresponding transmitters (not shown in  FIG. 1 ). A localizer transmitter is located at a far end of a runway and a glide slope transmitter is located at an approach end of the runway. The localizer and glide slope transmitters and receivers ( 50 , 60 ) aid a pilot in properly aligning an aircraft with the runway for landing. The localizer is utilized for a lateral alignment, and the glide slope for maintaining a proper vertical approach angle to the runway. 
     The database  16  may include location information (i.e. latitude, longitude, and elevation) for each respective VOR transmitter, localizer transmitter, and glide slope transmitter. In addition, runway lengths and glide path angles are maintained in database  16  for various runways. In one embodiment, data within database  16  relating to VOR transmitter latitude and longitude are utilized along with aircraft position (latitude and longitude from GPS receiver) to determine a horizontal distance to the transmitter. As utilized herein, a horizontal distance is the distance along the ground between two points. The horizontal distance from the transmitter is utilized along with an angular deviation from a desired flight path, for example from VOR receiver  40 , to determine a linear deviation from a desired flight path. Utilizing the linear deviation, the flight guidance system  10  determines, for example, pitch and roll commands to steer the vehicle to the desired flight path. 
     In the case of VOR, the height above the VOR transmitter, sometimes referred to as a VOR station, is also utilized to determine a cone of confusion for the VOR station, as further described below. Data relating to runway length for individual runways is stored in database  16  which is utilized, along with an angular deviation from the desired flight path provided by localizer receiver  50 , to determine a linear deviation from a desired lateral approach to a runway. Data relating to glide path angles for individual runways is also stored in database  16 . Such data, along with an angular deviation from the desired glide path angle provided by glide slope receiver  60 , is utilized in determining a linear deviation from the desired glide path angle to a runway. 
       FIG. 2  is a diagram illustrating the parameters utilized in calculating a linear deviation, d, from the desired flight path  102 . VOR transmitter  100  operates to provide a direction to the transmitter  106 , sometimes referred to as VOR bearing, for an air vehicle  104 . The microprocessor  12  (shown in  FIG. 1 ) determines the difference between the desired course  102  and the current VOR bearing  106  as an angular deviation  108 , denoted as ε. While a pilot would want to change their flight path to that of the desired course  102 , an angular deviation does not provide much guidance. For example, if air vehicle  104  is 100 miles from the VOR transmitter  100 , an angular deviation of three degrees results in a linear deviation  110  in excess of five miles from the desired flight path  102 . However, if air vehicle  104  is only five miles from the VOR transmitter  100 , an angular deviation of three degrees results in a linear deviation of about 0.26 miles from the desired flight path  102 . From this simple example it is seen that a linear deviation is most useful in correcting a flight path of an air vehicle  104 . 
     In one embodiment, for VOR operation, the flight guidance system  10  (shown in  FIG. 1 ) uses the VOR transmitter  100  location data stored in the database  16  along with the current air vehicle position from GPS receiver  30  to determine a horizontal distance, D, to the VOR transmitter  100 . This distance is used along with the angular deviation  108 , ε, as determined by VOR receiver  40  to determine a linearized deviation  110  from the desired flight path  102 . The determination of the linear deviation  110  results in improved flight director and auto pilot tracking. For example, a bank (or turn) angle needed to reduce or eliminate the linear deviation  110  is displayed on pilot display  20  (shown in  FIG. 1 ). 
     Therefore, to linearize the signal from VOR receiver  40 , all that is needed is the horizontal distance to the VOR transmitter  100  and the angular deviation  108 , ε, provided by VOR receiver  40 . Using data relating to the VOR transmitter latitude and longitude from database  16  along with the GPS data for present latitude and longitude provides the horizontal distance, D. The resultant linearized deviation is calculated according to: VOR linear deviation=d=D×Sin(ε). Utilizing the linear deviation, d, the flight guidance system  10  determines roll commands to steer the vehicle to the desired path  102 . 
     Flight guidance system  10  also utilizes an elevation of VOR transmitter  100  from database  16  and barometric altitude data to determine a height of air vehicle  104  above the VOR transmitter  100 . With such data and the horizontal distance D, flight guidance system  10  is able to determine a consistent “cone of confusion” extending above the VOR transmitter. As is further described below, the flight guidance system  10  will use dead reckoning to navigate the air vehicle through the cone of confusion, since the transmitter antenna pattern of VOR transmitter  100  will preclude stable signals being received by VOR receiver  40  (shown in  FIG. 1 ) in this region. 
       FIG. 3  illustrates a cone of confusion  150  created by an antenna array pattern at VOR transmitter  100 . To estimate a boundary for the cone of confusion  150 , a height, H, above the VOR transmitter  100  is required. This height is found by utilization of the elevation data for VOR transmitter  100  from database  16  and the present aircraft baro-corrected altitude from an air data system (e.g. altitude data  70 ). The difference between the two is the height, H. The cone of confusion is then defined by the ratio of height, H above the station to the distance to the station, D, as defined above. Determination of whether air vehicle  104  is within the cone of confusion  150 , and therefore signals originating from VOR transmitter  100  are no longer useful, is a logical expression. If H&gt;D×tan(Cone Angle), where Cone Angle is nominally 60 degrees, then air vehicle  104  is in the cone of confusion  150 , and a pilot should utilize dead-reckoning to navigate through the cone, essentially acting as if the linear deviation, d, is zero. 
       FIG. 4  illustrates operation of the localizer portion of the ILS for linearization of an angular deviation from a desired path, according to another embodiment of the present invention. As described above, a localizer transmitter  200  transmits localizer signals which are received by localizer receiver  50  which then determines an azimuth, or angular lateral deviation from a desired path  204  to guide the air vehicle  104  to the centerline  206  of runway  208 . As is shown in  FIG. 4 , localizer transmitter  200  is located at an end of runway  208  that is opposite an approaching air vehicle  104 . 
     To determine a linear deviation from desired path  204  utilizing the localizer signal, the flight guidance system  10  utilizes the data relating to location for the localizer transmitter  200  from the database  16  along with the current position of air vehicle  104  as determined through GPS receiver  30  to determine a horizontal distance, D, to the localizer transmitter  200 . This distance, D is utilized along with a runway length, RL, from the database  16 , and the angular deviation, ε, as determined by the localizer system (transmitter  200 , localizer receiver  50 ) into a linear deviation  210 , d, with a constant scale factor to improve auto pilot tracking and performance of the flight guidance system  10 . 
     Specifically, to linearize the deviation from the localizer portion of the ILS, an end of runway deviation, y, is first determined through normalization of the localizer angular deviation by accounting for the constant beam width of 350 feet full scale at the threshold (approach end) of all runways. A full scale value (350 feet from a centerline of the runway  208  at the end of the runway opposite the localizer transmitter  200 ) for localizer angular deviation is represented as 0.155 DDM (difference in depth of modulation) at an output of the localizer receiver  50 . A difference in depth of modulation occurs because the localizer transmitter  200  transmits two modulated signals. 
     Therefore, an end of runway deviation is calculated as 
             y   =         ɛ     0.155   ⁢           ⁢   DDM       ×   350   ⁢           ⁢   feet     =       2558   ⁢           ⁢     ɛ   ⁡     (   ft   )         =     688.258   ⁢           ⁢       ɛ   ⁡     (   m   )       .                 
To then determine a linear deviation, d, at the air vehicle  104  from the desired path  204 , the distance D, to localizer transmitter, and the database value for the length of the runway, RL, along with the end of runway deviation, y, is are utilized according to
 
             d   =         D   ×   y           RL   2     +     y   2           .           
Such an approach by an air vehicle  104  is sometimes referred to as an ILS front course approach.
 
     Sometimes, perhaps due to wind conditions, an aircraft  104  must approach the runway  208  in a direction that is opposite to the approach direction intended when the localizer transmitter  200  was installed. Such an approach is sometimes referred to as a back course approach. Determination of a linear deviation from a desired back course approach is illustrated in  FIG. 5 . During a back course approach, the localizer transmitter  200  is located at the approach end of the runway  208 . As above, the localizer transmitter  200  transmits localizer signals which are received by localizer receiver  50  which then determines an azimuth, or angular lateral deviation from a desired path  230  to guide the air vehicle  104  to the centerline  206  of runway  208 , albeit from the opposite direction. The linearization equations are the same for back course approach as the ILS front course approach described above except for a change in sign. 
     Therefore, an end of runway deviation is calculated as 
             y   =         ɛ     0.155   ⁢           ⁢   DDM       ×   350   ⁢           ⁢   feet     =       2558   ⁢           ⁢     ɛ   ⁡     (   ft   )         =     688.258   ⁢           ⁢       ɛ   ⁡     (   m   )       .                 
To then determine a linear deviation  232 , d, at the air vehicle  104  from the desired path  230 , the distance D, to the localizer transmitter, and the database value for the length of the runway, RL, along with the end of runway deviation, y, are utilized according to
 
     
       
         
           
             d 
             = 
             
               - 
               
                 
                   
                     D 
                     × 
                     y 
                   
                   
                     
                       
                         RL 
                         2 
                       
                       + 
                       
                         y 
                         2 
                       
                     
                   
                 
                 . 
               
             
           
         
       
     
       FIG. 6  illustrates operation of the glide slope portion of the ILS. Specifically, to determine a linear deviation from the glide slope path  250 , the flight guidance system  10  uses data relating to a location for the glide slope transmitter  252  from the database  16  along with the current aircraft position from GPS receiver  30  to determine a horizontal distance, D, to the glide slope transmitter  252 . This horizontal distance, D, is used along with the glide path angle  254  from the database  16  to convert an angular altitude deviation signal received from glide slope receiver  60  into a linearized deviation, d,  256  with a constant scale factor to improve autopilot tracking and operation of flight guidance system  10 . 
     To linearize the angular error from the glide path angle utilizing the glide slope portion of the ILS, the distance, D, to the glide slope transmitter  252  is used. The distance, D, is determined as the difference between air vehicle position, provided by GPS receiver  30  and data relating to the location of the glide slope transmitter  252  from database  16 . In one embodiment, the database  16  does not include data relating to a position of the glide slope transmitter  252 . Rather, in such an embodiment, data relating to a position of the localizer transmitter  200  along with data relating to runway length are utilized to estimate a position of the glide slope transmitter  252 . 
     The glide path angle, GPA, stored in database  16 , and height above the station, H, which is derived from the transmitter  252  elevation in database  16 , and elevation of air vehicle  104  (from either a GPS or an air data computer  70  (shown in  FIG. 1 )) are utilized to determine if an unwanted side lobe of the glide slope signal is being received, as opposed to the desired main beam. This determination of main/side lobe helps to prevent false captures. 
       FIG. 6  shows the geometry of the linearization, where ε is the GS deviation error in DDM, and the full scale (F.S.) value for glide slope deviation is represented as 0.175DDM at the glide slope receiver  60  output, corresponding to 0.2×GPA from the database  16 . The glide slope deviation error angle in radians is 
               α   =       ɛ     0.175   ⁢           ⁢   DDM       ×   0.2   ⁢           ⁢   GPA       ,         
and the glide slope linear deviation is
 
             d   =       D     cos   ⁡     (       G   ⁢           ⁢   P   ⁢           ⁢   A     -   α     )         ×       sin   ⁡     (   α   )       .             
If (0.75×GPA)&lt;arctan(H/D)&lt;(1.5×GPA), then capture is allowed.
 
       FIG. 7  is a flowchart  300  illustrating the methods disclosed herein for linearizing a deviation from a VOR bearing signal. Referring to flowchart  300 , a pilot selects  302  a flight course. Flight guidance system  10  (shown in  FIG. 1 ) receives  304  a VOR bearing from the VOR receiver  40  (shown in  FIG. 1 ). The flight guidance system  10  retrieves  306  a position (i.e. latitude, longitude, and elevation) of the VOR transmitter  100  (shown in  FIG. 2 ). The flight guidance system  10  then receives  308  a vehicle position (i.e. latitude, longitude, and elevation) from a GPS receiver  30  (shown in  FIG. 1 ). The flight guidance system  10  calculates  310  a linear deviation from the VOR bearing utilizing the methodology described with respect to  FIG. 2 . Upon calculation  310  of the linear deviation, the flight guidance system  10  is configured to calculate  312  a roll command that corresponds to a roll that is needed to minimize the deviation from the VOR bearing signal. The pilot then decides  314  whether the roll command is to be executed manually or through an auto pilot system. 
       FIG. 8  is a flowchart  350  illustrating the methods disclosed herein for linearizing a deviation from a center of a localizer signal that is a portion of the functionality provided by an ILS. The method is similar to that associated with determining a linear deviation from a VOR bearing (shown in  FIG. 7 ). Referring to flowchart  350 , a pilot selects  352  a flight course. Flight guidance system  10  (shown in  FIG. 1 ) receives  354  localizer data from the localizer receiver  50  (shown in  FIG. 1 ). The localizer data is in the form of a deviation from a null between the localizer&#39;s transmitted beams. The flight guidance system  10  retrieves  356  a position (i.e. latitude, longitude, elevation, and runway length) of the runway associated with the localizer transmitter  200  (shown in  FIG. 4 ). The flight guidance system  10  then receives  358  a vehicle position (i.e. latitude, longitude, and elevation) from a GPS receiver  30  (shown in  FIG. 1 ). The flight guidance system  10  calculates  360  a linear deviation from the localizer signal utilizing the methodology described with respect to  FIG. 4 . Upon calculation  360  of the linear deviation, the flight guidance system  10  is configured to calculate  362  a roll command that corresponds to a roll that is needed to minimize the deviation from the localizer signal. The pilot then decides  364  whether the roll command is to be executed manually or through an auto pilot system. A method similar to that illustrated by flowchart  350  is utilized in determining a linear deviation from a desired path for a back course approach to a runway. 
       FIG. 9  is a flowchart  400  illustrating the methods disclosed herein for linearizing an angular altitude deviation from the ILS glide path. The glide slope angular altitude deviation is a portion of the functionality provided by an ILS. The method is similar to that associated with determining a linear deviation from a VOR bearing (shown in  FIG. 7 ). Referring to flowchart  400 , flight guidance system  10  (shown in  FIG. 1 ) receives  404  a glide slope error angle from the glide slope receiver  60  (shown in  FIG. 1 ). The flight guidance system  10  retrieves  406  a position (i.e. latitude, longitude, elevation) and a glide path angle that is defined for the runway associated with glide slope transmitter  252  (shown in  FIG. 6 ). The flight guidance system  10  then receives  408  a vehicle position (i.e. latitude, longitude, and elevation) from a GPS receiver  30  (shown in  FIG. 1 ). The flight guidance system  10  calculates  410  a linear deviation from the glide path angle utilizing the methodology described with respect to  FIG. 6 . Upon calculation  410  of the linear deviation, the flight guidance system  10  calculates  412  a pitch command that is needed to reduce the deviation from the glide path angle. The pilot then decides  414  whether the pitch command is to be executed manually or through an auto pilot system. 
     The described systems and methods are able to achieve improved performance over classical linearization methods, due to the use of database parameters to get actual values for different installations rather than assuming default values. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.