Patent Publication Number: US-8527233-B2

Title: Airspeed sensing system for an aircraft

Description:
BACKGROUND INFORMATION 
     1. Field 
     The present disclosure relates generally to sensor systems and more specifically to airspeed sensor systems. 
     2. Background 
     Sensor systems for aircraft provide flight data to pilots. These sensor systems provide data such as altitude, airspeed, heading, and pitch to pilots to enable them to operate the aircraft. For example, pilots may use heading data to determine when the aircraft is traveling in the direction of the destination of the aircraft. 
     The sensor systems are also used by computer systems that control systems onboard the aircraft. For example, airspeed may be used by computer systems onboard the aircraft to control the speed and stability of the aircraft. 
     True airspeed is the actual speed of an aircraft relative to the air in which the aircraft is flying. Calibrated airspeed is the speed of the aircraft as identified by sensor systems onboard the aircraft. Calibrated airspeed differs from true airspeed in that calibrated airspeed is uncorrected for the effects of the compressibility and density of the air surrounding the aircraft at the time of measurement. As used herein, calibrated airspeed is referred to as airspeed. 
     Airspeed is an example of a measurement made by a sensor system for an aircraft. Different types of sensors may be used in the sensor system used to measure airspeed. For example, a pitot-static tube may be used to measure airspeed. A pitot-static tube measures airspeed by identifying the total and static pressures in the environment surrounding the aircraft. 
     Different conditions may change the accuracy with which a sensor measures airspeed. For example, ice may accumulate in or around an airspeed sensor. The ice may cause the airspeed sensors to report an airspeed for the aircraft that is less accurate than desired. 
     With a decreased accuracy in detecting the airspeed of an aircraft, the data reported by the sensor systems to a pilot and/or onboard computer systems by the sensor system may reduce the performance of the aircraft. For example, airspeed and other information may be used to maintain the aircraft speed at an acceptable value. If the airspeed is not as accurate as desired, control of the airplane may become compromised. 
     Accordingly, it would be advantageous to have a method and apparatus which takes into account one or more of the issues discussed above, as well as possibly other issues. 
     SUMMARY 
     The different advantageous embodiments provide an apparatus and method for identifying an airspeed for an aircraft. In one advantageous embodiment, an apparatus is provided. The apparatus consists of a plurality of pitot-static probes. Each of the plurality of pitot-static probes is a first sensor type. The plurality of pitot-static probes generate a first data. The apparatus also consists of a plurality of angle of attack sensor systems. Each of the plurality of angle of attack sensor systems is a second sensor type, and the plurality of angle of attack sensor systems generates a second data. The apparatus also consists of a plurality of light detection and ranging sensors. Each of the plurality of light detection and ranging sensor systems is a third sensor type, and the plurality of light detection and ranging sensor systems generates a third data. The apparatus also consists of signal consolidation system configured to detect errors in the first data generated by the plurality of pitot-static probes, the second data generated by the plurality of angle of attack sensor systems, and the third data generated by the plurality of light detection and ranging sensors. 
     In another advantageous embodiment, an apparatus consists of a plurality of pitot-static probes, a plurality of angle of attack sensor systems, a plurality of Venturi tubes, and a signal consolidation system. Each of the plurality of pitot-static probes is a first sensor type. The plurality of pitot-static probes is configured to generate first data. Each of the plurality of angle of attack sensor systems is a second sensor type, and the plurality of angle of attack sensor systems is configured to generate second data. Each of the plurality of Venturi tubes is a third sensor type, and the plurality of Venturi tubes is configured to generate third data. The signal consolidation system is configured to detect errors in the first data generated by the plurality of pitot-static probes, the second data generated by the plurality of angle of attack sensor systems, and the third data generated by the plurality of Venturi tubes. 
     In yet another advantageous embodiment, a method for identifying an airspeed of an aircraft is provided. A plurality of pitot-static probes generates a first total pressure value and a first static pressure value for an environment surrounding the aircraft. A plurality of light detection and ranging sensors generates a second total pressure value and a second static pressure value for the environment surrounding the aircraft. A plurality of angle of attack sensor systems generate a third total pressure value and a third static pressure value for the environment surrounding the aircraft. Errors in the first total pressure value, the first static pressure value, the second total pressure value, the second static pressure value, the third total pressure value, and the third static pressure value are consolidated to form a consolidated total pressure value and a consolidated static pressure value. An airspeed is identified for the aircraft from the consolidated total pressure value and the consolidated static pressure value. 
     The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the advantageous embodiments are set forth in the appended claims. The advantageous embodiments, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an advantageous embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an illustration of an aircraft depicted in accordance with an advantageous embodiment; 
         FIG. 2  is an illustration of a data processing system depicted in accordance with an advantageous embodiment; 
         FIG. 3  is an illustration of an airspeed monitoring environment depicted in accordance with an advantageous embodiment; 
         FIG. 4  is an illustration of a Venturi tube depicted in accordance with an advantageous embodiment; 
         FIG. 5  is an illustration of a signal consolidation system depicted in accordance with an advantageous embodiment; 
         FIG. 6  is an illustration of total pressure values depicted in accordance with an advantageous embodiment; 
         FIG. 7  is a second illustration of total pressure values depicted in accordance with an advantageous embodiment; 
         FIG. 8  is an illustration of a flowchart of a process for identifying an airspeed of an aircraft depicted in accordance with an advantageous embodiment; and 
         FIG. 9  a flowchart of a process for detecting errors depicted in accordance with an advantageous embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Looking now to the figures, and with specificity to  FIG. 1 , an illustration of an aircraft is depicted in accordance with an advantageous embodiment. Aircraft  100  is an example of an aircraft in which advantageous embodiments may be implemented. 
     Aircraft  100  is made up of fuselage section  102  and tail section  104 . Fuselage section  102  is the main body of aircraft  100  that contains the passengers and crew onboard aircraft  100 . Fuselage section  102  also contains flight data processing system  114 . 
     Fuselage section  102  also contains forward section  106 . Forward section  106  is an area of fuselage section  102  located forward of wing  116 . Forward section  106  contains cockpit  118 , and flight data processing system  114 . 
     Forward section  106  also contains airspeed sensor systems  108 ,  110 ,  112 , and  120 . In these examples, airspeed sensor system  108  consists of pitot-static probes, and airspeed sensor system  110  consists of angle of attack sensors. Airspeed sensor system  112  consists of light detection and ranging (LIDAR) sensors in these examples. Airspeed sensor system  120  consists of Venturi tubes in these examples. 
     Airspeed sensor system  110  identifies the airspeed of aircraft  100  using the angle of attack of aircraft  100 , global positioning system data from global positioning system sensor  122  and inertial system data from inertial sensor system  126 . The angle of attack of aircraft  100  is the angle between the longitudinal principal axis of aircraft  100  and the local air mass flow. The global positioning system data contains an altitude of aircraft  100 . Inertial sensor system  126  is a plurality of Schuler-tuned inertial reference units. For example, Schuler-tuned inertial reference units may be used in commercial transport aircraft. Additionally, inertial sensor system  126  consists of laser-gyro inertial reference units. 
     Airspeed sensor system  110  combines the angle of attack, the global positioning data from global positioning system  122 , and the inertial system data to identify a static pressure and a total pressure for the environment around aircraft  100 . In some advantageous embodiments, static pressure and total pressure are identified from the angle of attack, global positioning data from global positioning system  122 , and the inertial system data using a lift model. An example of a lift model is described in U.S. patent application Ser. No. 12/255,233, status pending, published as U.S. Pat. Pub. No. 2010/0100260, which is incorporated herein by reference. 
     Airspeed sensor system  110  identifies the airspeed of aircraft  100  using pitot-static probes. Pitot-static probes identify airspeed by measuring the static pressure and the total pressure of the environment surrounding aircraft  100 . The pitot-static probes consist of cantilevered tubes pointed in the direction of flight and which measure the stagnation (total) pressure of the air at the tip of the tube, and the ambient (static) pressure along the side of the tube. Alternatively the probe may measure pitot pressure only and static pressure may be measured by flush ports along the side of the forward aircraft body. Airspeed sensor system  110  identifies the static pressure and the total pressure of the environment surrounding aircraft  100 . 
     In some advantageous embodiments, airspeed data system  112  is present and airspeed sensor system  120  is absent. However, in other advantageous embodiments, both airspeed data system  112  and airspeed sensor system  120  are present. 
     Airspeed sensor system  120  identifies airspeed of aircraft  100  using Venturi tubes. A Venturi tube is a pipe that has at least two sections, wherein each section has a different diameter. Air enters airspeed sensor system  120  as aircraft  100  moves through the air. The air flows into one section, and then into the other section. The air has a different pressure in each section of the pipe. 
     The pressure differential between the fluid in the two sections and the static pressure of the environment surrounding aircraft  100  may be identified. The static pressure may be identified at the point at which the air enters the pipe. The pressure differential may be measured by measuring pressures in both sections of the Venturi tube and subtracting the pressure in one section from the pressure in the other section. The pressure differential may be used to obtain the total pressure for the environment surrounding aircraft  100 . 
     Airspeed data system  112  is associated with tail section  104 . Airspeed data system  112  consists of light detection and ranging (LIDAR) sensors in these examples. Airspeed data system  112  uses lasers to monitor the distance traveled by aircraft  100  over a period of time. The distance and the period of time are used to identify an airspeed for aircraft  100 . 
     Flight data system  114  receives total pressure and static pressure from airspeed sensor systems  108 ,  110 , and  120 . 
     Turning now to  FIG. 2 , a diagram of a data processing system is depicted in accordance with an advantageous embodiment. Data processing system  200  may be used to implement computer system  308  in  FIG. 3 . Data processing system  200  may be used as an aircraft data system for identifying an airspeed for an aircraft, such as aircraft  100  in  FIG. 1 . 
     In this advantageous embodiment, data processing system  200  includes communications fabric  202 , which provides communications between processor unit  204 , memory  206 , persistent storage  208 , communications unit  210 , input/output (I/O) unit  212 , and display  214 . 
     Processor unit  204  serves to execute instructions for software that may be loaded into memory  206 . Processor unit  204  may be a set of one or more processors or may be a multi-processor core, depending on the particular implementation. Further, processor unit  204  may be implemented using one or more heterogeneous processor systems, in which a main processor is present with secondary processors on a single chip. As another advantageous example, processor unit  204  may be a symmetric multi-processor system containing multiple processors of the same type. 
     Memory  206  and persistent storage  208  are examples of storage devices  216 . A storage device is any piece of hardware that is capable of storing information, such as, for example, without limitation, data, program code in functional form, and/or other suitable information either on a temporary basis and/or a permanent basis. Memory  206 , in these examples, may be, for example, a random access memory, or any other suitable volatile or non-volatile storage device. Persistent storage  208  may take various forms, depending on the particular implementation. For example, persistent storage  208  may contain one or more components or devices. For example, persistent storage  208  may be a hard drive, a flash memory, a rewritable optical disk, a rewritable magnetic tape, or some combination of the above. The media used by persistent storage  208  may be removable. For example, a removable hard drive may be used for persistent storage  208 . 
     Communications unit  210 , in these examples, provides for communication with other data processing systems or devices. In these examples, communications unit  210  is a network interface card. Communications unit  210  may provide communications through the use of either or both physical and wireless communications links. 
     Input/output unit  212  allows for the input and output of data with other devices that may be connected to data processing system  200 . For example, input/output unit  212  may provide a connection for user input through a keyboard, a mouse, and/or some other suitable input device. Further, input/output unit  212  may send output to a printer. Display  214  provides a mechanism to display information to a user. 
     Instructions for the operating system, applications, and/or programs may be located in storage devices  216 , which are in communication with processor unit  204  through communications fabric  202 . In these advantageous embodiments, the instructions are in a functional form on persistent storage  208 . These instructions may be loaded into memory  206  for execution by processor unit  204 . The processes of the different embodiments may be performed by processor unit  204  using computer implemented instructions, which may be located in a memory, such as memory  206 . 
     These instructions are referred to as program code, computer usable program code, or computer readable program code that may be read and executed by a processor in processor unit  204 . The program code, in the different embodiments, may be embodied on different physical or computer readable storage media, such as memory  206  or persistent storage  208 . 
     Program code  218  is located in a functional form on computer readable media  220  that is selectively removable and may be loaded onto or transferred to data processing system  200  for execution by processor unit  204 . Program code  218  and computer readable media  220  form computer program product  222 . In one example, computer readable media  220  may be computer readable storage media  224  or computer readable signal media  226 . Computer readable storage media  224  may include, for example, an optical or magnetic disc that is inserted or placed into a drive or other device that is part of persistent storage  208  for transfer onto a storage device, such as a hard drive, that is part of persistent storage  208 . Computer readable storage media  224  also may take the form of a persistent storage, such as a hard drive, a thumb drive, or a flash memory that is connected to data processing system  200 . In some instances, computer readable storage media  224  may not be removable from data processing system  200 . 
     Alternatively, program code  218  may be transferred to data processing system  200  using computer readable signal media  226 . Computer readable signal media  226  may be, for example, a propagated data signal containing program code  218 . For example, computer readable signal media  226  may be an electro-magnetic signal, an optical signal, and/or any other suitable type of signal. These signals may be transmitted over communications links, such as wireless communications links, an optical fiber cable, a coaxial cable, a wire, and/or any other suitable type of communications link. In other words, the communications link and/or the connection may be physical or wireless in the advantageous examples. 
     In some advantageous embodiments, program code  218  may be downloaded over a network to persistent storage  208  from another device or data processing system through computer readable signal media  226  for use within data processing system  200 . For instance, program code stored in a computer readable storage media in a server data processing system may be downloaded over a network from the server to data processing system  200 . The data processing system providing program code  218  may be a server computer, a client computer, or some other device capable of storing and transmitting program code  218 . 
     The different components illustrated for data processing system  200  are not meant to provide architectural limitations to the manner in which different embodiments may be implemented. The different advantageous embodiments may be implemented in a data processing system including components in addition to or in place of those illustrated for data processing system  200 . Other components shown in  FIG. 2  can be varied from the advantageous examples shown. The different embodiments may be implemented using any hardware device or system capable of executing program code. As one example, data processing system  200  may include organic components integrated with inorganic components and/or may be comprised entirely of organic components excluding a human being. For example, a storage device may be comprised of an organic semiconductor. 
     As another example, a storage device in data processing system  200  is any hardware apparatus that may store data. Memory  206 , persistent storage  208 , and computer readable media  220  are examples of storage devices in a tangible form. 
     In another example, a bus system may be used to implement communications fabric  202  and may be comprised of one or more buses, such as a system bus or an input/output bus. Of course, the bus system may be implemented using any suitable type of architecture that provides for a transfer of data between different components or devices attached to the bus system. Additionally, a communications unit may include one or more devices used to transmit and receive data, such as a modem or a network adapter. Further, a memory may be, for example, memory  206  or a cache such as found in an interface and memory controller hub that may be present in communications fabric  202 . 
     The different advantageous embodiments recognize and take into account a number of different considerations. For example, the different advantageous embodiments recognize and take into account that a common mode event may cause inconsistent data to be reported by more than one sensor used to determine airspeed. A common mode event is an event that adversely affects more than one sensor of the same type. For example, ice accumulation may adversely affect a plurality of pitot-static probes at the same time. 
     The different advantageous embodiments recognize that some types of sensors are not likely to be affected by the same common mode event as other types of sensors. The sensors may not be affected by the same event due to the design of the sensors and/or the location of the sensors. For example, ice may not affect a second or third type of airspeed sensor because of the location of the airspeed sensor or the design of the sensor is not affected by ice. 
     Additionally, the different advantageous embodiments recognize that receiving airspeed and/or pressure data from two different sensor system types does not allow the aircraft data consolidation system receiving the airspeed and/or pressure data to identify which airspeed data sensor system type is reporting an accurate value in the event there is an inconsistency in the data received from the two sensor types. 
     The different advantageous embodiments recognize that receiving pressure and/or airspeed data from at least three different airspeed data sensor system types allow the aircraft data system to identify which single sensor type is reporting inconsistent values by comparing the values to the values obtained using the other two sensor types. 
     Thus, the different advantageous embodiments provide an apparatus and method for identifying an airspeed for an aircraft. In one advantageous embodiment, an apparatus is provided. The apparatus consists of a plurality of pitot-static probes. Each of the plurality of pitot-static probes is a first sensor type. The plurality of pitot-static probes generate first data. The apparatus also consists of a plurality of angle of attack sensor systems. Each of the plurality of angle of attack sensor systems is a second sensor type, and the plurality of angle of attack sensor systems generate second data. The apparatus also consist of a plurality of light detection and ranging sensors. The plurality of light detection and ranging sensors generate third data. The apparatus also consists of a signal consolidation system configured to detect errors in the first data generated by the plurality of pitot-static probes, the second data generated by the plurality of angle of attack sensor systems and the third data generated by the plurality of light detection and ranging sensors. 
     In another advantageous embodiment, an apparatus consists of a plurality of pitot-static probes, a plurality of angle of attack sensor systems, a plurality of Venturi tubes, and a signal consolidation system. Each of the plurality of pitot-static probes is a first sensor type. The plurality of pitot-static probes are configured to generate first data. Each of the plurality of angle of attack sensor systems is a second sensor type, and the plurality of angle of attack sensor systems are configured to generate second data. Each of the plurality of Venturi tubes is a third sensor type, and the plurality of Venturi tubes are configured to generate third data. The signal consolidation system is configured to detect errors in the first data generated by the plurality of pitot-static probes, the second data generated by the plurality of angle of attack sensor systems, and the third data generated by the plurality of Venturi tubes. 
     In yet another advantageous embodiment, a method for identifying an airspeed of an aircraft is provided. A plurality of pitot-static probes generate a first total pressure value and a first static pressure value for an environment surrounding the aircraft. A plurality of light detection and ranging sensors generate a second total pressure value and a second static pressure value for the environment surrounding the aircraft. A plurality of angle of attack sensor systems generate a third total pressure value and a third static pressure value for the environment surrounding the aircraft. The first total pressure values, the first static pressure values, the second total pressure values, the second static pressure values, the third total pressure values, and the third static pressure values are consolidated to form a consolidated total pressure value and a consolidated static pressure value. An airspeed is identified for the aircraft from the consolidated total pressure value and the consolidated static pressure value. 
     Turning now to  FIG. 3 , an illustration of an airspeed monitoring environment is depicted in accordance with an advantageous embodiment. Airspeed monitoring environment  300  may be used to monitor the airspeed of aircraft  100  in  FIG. 1 . 
     Airspeed monitoring environment  300  contains environment  302 . Environment  302  is a physical area that surrounds aircraft  304 . Aircraft  100  in  FIG. 1  is an example of aircraft  304 . Sensor systems  306  and computer system  308  are onboard aircraft  304 . In these examples, computer system  308  is located on the interior of aircraft  304  and sensor systems  306  are located on the outside of aircraft  304 . 
     Sensor systems  306  are used by computer system  308  to identify airspeed  310  of aircraft  304 . Sensor systems  306  consist of sensors of sensor types  320 ,  322 ,  324 , and  326 . Sensor types  320 ,  322 ,  324 , and  326  are different types of sensors such that an event that may cause one sensor type to generate inconsistent data does not cause another sensor type to generate inconsistent data. 
     In these examples, sensor type  320  is plurality of pitot-static probes  312 , sensor type  322  is plurality of angle attack sensor systems  314 , sensor type  324  is plurality of light detection and ranging sensors  316 , and sensor type  326  is plurality of Venturi tubes  318 . It should be noted that in some advantageous embodiments, plurality of light detection and ranging sensors  316  is present and plurality of Venturi tubes  318  is absent. Likewise, in other advantageous embodiments, plurality of Venturi tubes  318  is present and plurality of light detection and ranging sensors  316  is absent. 
     Plurality of pitot-static probes  312  are tubes that point forward on aircraft  304  in the direction of travel. Air impinges on plurality of pitot-static probes  312  while aircraft  304  is in motion. As the speed of aircraft  304  increases, the air causes the total pressure in plurality of pitot-static probes  312  to increase. Plurality of pitot-static probes  312  generates data  328 . In these examples, data  328  consists of total pressure value  330  and static pressure value  332 . Total pressure value  330  is a value for the total pressure of air around aircraft  304  as a result of aircraft  304  being in motion. Static pressure value  332  is a value for the static pressure of the atmosphere in environment  302 . 
     The static pressure and total pressure are used to identify the airspeed of aircraft  100  using Bernoulli&#39;s equation for compressible flow as follows:
 
 V   c   =C   so  (5 (( P   t   −P   s )/ P   so +1) 2/7 −1)) 1/2 ,
 
where P t  is total pressure for the environment surrounding aircraft  100 , P s  is static pressure for the environment surrounding aircraft  100 , P so  is the standard day static pressure at sea-level, C so  is the speed of sound at sea-level, standard day is a term used to describe a set of atmospheric data tables showing temperature, pressure and density as a function of altitude, and V c  is the calibrated airspeed of aircraft  100 .
 
     Plurality of pitot-static probes  312  is located on forward portion  334  of fuselage  336 . Fuselage  336  is an example implementation of fuselage portion  102  in  FIG. 1 . 
     Plurality of angle of attack sensor systems  314  measure the angle of attack of aircraft  304 . Angle of attack is the angle of the longitudinal principal axis of aircraft  304  with respect to the direction of the airflow. Angle of attack sensor systems  314  generate data  338 . In these examples, angle of attack sensor systems  314  generate synthetic total pressure value  340  and synthetic static pressure value  342  by using angle of attack vane sensor  344 , altitude as identified by global positioning system (GPS) receiver  346 , and inertial data from inertial sensor system  378 . Data  338 , inertial data from inertial sensor system  378 , and altitude as identified by global positioning system receiver  346  are used to solve an aircraft lift model for synthetic total pressure value  340 . One example of a lift model that may be solved to identify total and static pressure is as follows: 
     
       
         
           
             
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     where C L  is the lift coefficient, C L0  is the lift coefficient at angle of attack equal to zero, ΔC L  is the change in the lift coefficient caused by high-lift and movable surfaces, C Lα  is the slope of the lift coefficient as a function of alpha, α is the angle of attack of aircraft  304 , W is the gross weight of aircraft  304 , n z  is the load factor of aircraft  304 , q_bar is the dynamic pressure, and S is the reference area of the wings of aircraft  304 . 
     Examples of movable surfaces include elevators, horizontal stabilizers, ailerons, rudders, trim tabs, spoilers, flaps, slats, and other movable surfaces. This lift model is a simple lift model in these examples. However, in other advantageous embodiments, more complex lift models may be used. A complex lift model includes additional mathematical features than a simple lift model. For example, the complex lift model may include additional mathematical variables, operations, and functions not present in the simple lift model. 
     The result of the aircraft lift model is to derive total and static pressure. Identifying synthetic total pressure value  340  and synthetic static pressure value  342  by using angle of attack vane sensor  344 , altitude as identified by global positioning system (GPS) receiver  346 , and inertial data from inertial sensor system  378  in an example of a lift model that is described in U.S. patent application Ser. No. 12/255,233, status pending, published as U.S. Pat. Pub. No. 2010/0100260, which is incorporated herein by reference. 
     Global positioning system receiver  346  identifies altitude above mean sea level  348  of aircraft  304 . Plurality of angle of attack sensor systems  314  uses altitude above mean sea level  348  to generate synthetic static pressure  352 . Synthetic static pressure  352  is an approximation of static pressure value  342  in environment  302  at altitude above mean sea level  348 . Static pressure value  342  is set to the value of synthetic static pressure  352  in these examples. 
     Plurality of angle of attack sensor systems  314  also generate total pressure value  340 . Plurality of angle of attack sensor systems  314  use the gross weight of aircraft  304  and inertial data of aircraft  304  to generate synthetic total pressure  354 . Synthetic total pressure  354  is used as total pressure value  340  in these examples. 
     Plurality of light detection and ranging sensors  316  (LIDAR) uses one or more lasers to generate data  356 . Data  356  consists of an airspeed for aircraft  304 . Light detection and ranging sensors  316  generates data  356  by using the one or more lasers to identify a distance traveled over a period of time. In some advantageous embodiments, light detection and ranging sensors  316  measure true airspeed of aircraft by measuring the doppler shift from Rayleigh backscatter from the air molecules and/or Mie backscatter from the aerosol particles in the air mass. Light detection and ranging sensors  316  also measure air ambient temperature and ambient pressure from the Rayleigh backscatter. From these data they compute the calibrated airspeed of aircraft  304  and the total and static pressures for the aircraft environment  302 . 
     In one advantageous embodiment the light detection and ranging sensors may be pointed in a rear-looking direction. Thus, the possibility of ice and large hail contacting the light detection and ranging sensors is reduced. In other advantageous embodiments, the light detection and ranging sensors may each make multiple measurements along directions that are not aligned with the direction of travel, but from which measurements the airspeed may be calculated by identifying the multiple components of velocity into the direction of travel. 
     In yet other advantageous embodiments, the light detection and ranging sensors may make their airspeed measurements at a distance outside the region of local airflow disturbance caused by the aircraft itself. In other advantageous embodiments, the light detection and ranging sensors may make their measurements at a very short distance from the aircraft, within the region of local airflow disturbance. Such measurements are then corrected for the effects of the local airflow. 
     In some advantageous embodiments, plurality of Venturi tubes  318  is present in sensor systems  306  and plurality of light detection and ranging sensors  316  is absent. Plurality of Venturi tubes  318  is a number of pipes that each have at least two sections, wherein each section of each pipe has a different diameter. Air enters plurality of Venturi tubes  318  as aircraft  304  moves through the air. The air flows into one section, and then into the other section. The air has a different pressure in each section of the pipe. 
     The pressure differential between the fluid in the two sections and static pressure  358  of environment  302  surrounding aircraft  304  may be identified. Static pressure value  358  may be identified at the point at which the air enters the pipe. The pressure differential may be measured by measuring pressures in both sections of the Venturi tube and subtracting the pressure in one section from the pressure in the other section. In one advantageous embodiment, plurality of Venturi tubes  318  consist of Venturi tubes in which the center section is narrower than the inlet section, that is, a divergent/convergent tube. A smaller presure differential generated in a Venturi tube in which the center section is narrower than the inlet section has the advantage that it operates successfully at high subsonic Mach numbers and may be used at substantially all subsonic speeds. 
     Total pressure value  360  is generated for environment  302  surrounding aircraft  304 . Plurality of Venturi tubes  318  generates data  362 . Data  362  is static pressure value  358  and total pressure  360  in these examples. In some advantageous embodiments, plurality of Venturi tubes  318  are located forward on fuselage  336  of wing fairing  364 . 
     Computer system  308  then runs signal consolidation system  366 . Signal consolidation system  366  detects errors  368  in data  328 , data  338 , data  356 , and/or data  362  by generating consolidated total pressure value  370  and consolidated static pressure value  372 . Errors may be present in data  328 , data  338 , data  356 , and/or data  362  because one or more events have caused one or more sensor systems  306  to generate inconsistent data. 
     For example, ice may accumulate in the inlets of plurality of pitot-static probes  312  and plurality of pitot-static probes  312  may generate inconsistencies in total pressure value  330  and/or static pressure value  332 . 
     Signal consolidation system  366  detects and isolates errors  368  by generating consolidated total pressure value  380  and consolidated static pressure value  372 . Consolidated static pressure value  372  is a value generated from some or all of static pressure values  332 ,  342 , and  358 . In these examples, consolidated static pressure value  372  is middle value  376  from static pressure values  332 ,  342 , and  358 . 
     Likewise, consolidated total pressure value  380  is a value generated from some or all of total pressure value  332 , total pressure value  340 , and total pressure value  360 . In these examples, consolidated total pressure value  380  is middle value  374  from total pressure values  332 ,  340 , and  360 . 
     Once consolidated total pressure value  380  and consolidated static pressure value  372  are generated, signal consolidation system  366  generates airspeed  310 . In these examples, airspeed  310  is calibrated airspeed of aircraft  304 . 
     In advantageous embodiments in which plurality of light detection and ranging sensors  316  is present, airspeed generated by plurality of light detection and ranging sensors  316  is compared with airspeed  310 . If the airspeed generated by light detection and ranging sensor  316  differs from airspeed  310  by more than a specified amount, the value for airspeed  310  may be modified. For example, airspeed  310  may be modified to the midpoint between the airspeed generated by plurality of light detection and ranging sensors  316 . 
     The illustration of airspeed monitoring environment  300  in  FIG. 3  is not meant to imply physical or architectural limitations to the manner in which different advantageous embodiments may be implemented. Other components in addition to and/or in place of the ones illustrated may be used. Some components may be unnecessary in some advantageous embodiments. Also, the blocks are presented to illustrate some functional components. One or more of these blocks may be combined and/or divided into different blocks when implemented in different advantageous embodiments. 
     For example, in some advantageous embodiments, plurality of Venturi tubes  318  are absent. In other advantageous embodiments, plurality of light detection and ranging sensors  316  is absent. In some advantageous embodiments, plurality of Venturi tubes  318  are located on the vertical stabilizer of aircraft  304 . 
     Looking now to  FIG. 4 , an illustration of a Venturi tube is depicted in accordance with an advantageous embodiment. Venturi tube  400  is an example of a Venturi tube in plurality of Venturi tubes  318 . 
     Venturi tube  400  extends from fuselage  402  in this advantageous embodiment. Fuselage  402  is an example implementation of fuselage  336  in  FIG. 3 . Arrow  403  indicates the forward direction on fuselage  402 . The forward direction indicated by arrow  403  is the direction in which the cockpit is located in this advantageous embodiment. Of course, in other advantageous embodiments, Venturi tube  400  may be located in other suitable locations. 
     Venturi tube  400  consists of tube  404  and tube  406 . Tube  404  and  406  extend from fuselage  402  through strut  401 . Ports  408  in tube  404  allows air traveling in region  410  to enter tube  404 . Air travels through tube  404  to connector  412 . The air traveling through tube  404  travels through connector  412 . Connector  412  connects tube  404  to sensor  414 . The pressure of the air in tube  404  is measured using sensor  414 . Sensor  414  is attached to connector  412  in this advantageous embodiment. Of course, sensor  414  may be connected to connector  412  using a tube, a channel, or other suitable device. 
     Likewise, ports  416  allow air traveling in region  410  to enter tube  406 . Tube  406  is like tube  404 , but is a different diameter than tube  404 . In this advantageous embodiment, tube  406  is twice the diameter of tube  404 . Thus, Venturi tube  400  is a divergent/convergent Venturi tube. 
     The air traveling through tube  406  travels through connector  418 . Connector  418  connects tube  406  to sensor  420 . The pressure of the air in tube  406  is measured using sensor  420 . Sensor  420  is attached to connector  418  in this advantageous embodiment. Of course, sensor  414  may be connected to connector  412  using a tube, a channel, or another suitable device. 
     Computer system  422  is an example implementation of computer system  308  in  FIG. 3 . Computer system  422  receives the pressure values from sensor  414  and sensor  420 . Computer system  422  then calculates the difference between the pressure values. The difference between the pressure values is used by computer system  422  to generate a total pressure value, such as total pressure value  360  in  FIG. 3 , for the environment in region  410 . 
     In some advantageous embodiments, one or more static pressure sensors may also be present. For example, a static pressure sensor may be located substantially adjacent to ports  408  and/or ports  416 . The static pressure values generated by static pressure sensors are sent to computer system  422  in such advantageous embodiments. 
     Turning now to  FIG. 5 , an illustration of a signal consolidation system is depicted in accordance with an advantageous embodiment. Signal consolidation system  500  is an example implementation of signal consolidation system  366  in  FIG. 3 . 
     Signal consolidation system  366  is implemented as a process in computer system  308  in  FIG. 3 . However, signal consolidation system  500  may instead be implemented using one or more of component  502 . Component  502  may be plurality of circuits  504 , plurality of integrated circuits  506 , and programmable logic array  508 . 
       FIGS. 6-7  illustrate an example of a signal consolidation system generating a consolidated total pressure value using total pressure values from sensor systems on an aircraft. Of course, consolidated static pressure may be generated in a similar manner as consolidated total pressure. 
     Turning now to  FIG. 6 , an illustration of total pressure values is depicted in accordance with an advantageous embodiment. Total pressure values  600  are example implementations of total pressure values  332 ,  340 , and  360  in  FIG. 3 . 
     Total pressure values  600  are shown after being generated by sensor systems, such as sensor systems  306  in  FIG. 3 . Sensor column  602  indicates the identity of the sensor that generated the value in total pressure column  604 . In this illustrative example, pitot-static sensors  606  generated values of about 26 and about 23. Likewise, angle of attack sensor systems  608  generated values of about 24 and about 22. Venturi tubes  610  generated values of about 14 and about 11. 
     A signal consolidation system, such as signal consolidation system  366  in  FIG. 3  processes total pressure values  600 . Assume the consolidated total pressure value last generated by the signal consolidation system was about 24. For each sensor type, the middle value among the two generated values and the last consolidated total pressure value is selected. 
     In this example, the middle value for pitot-static sensors  606  between 26, 23, and the last consolidated total pressure value of 24 is selected to form 24. Likewise, the middle value among the two generated values for angle of attack sensors  608  and the last consolidated total pressure value of 24 is selected to form 24. Additionally, the middle value among the two generated values for Venturi tubes  610  and the last consolidated total pressure value of 24 is selected to form 14. 
     Looking now to  FIG. 7 , a second illustration of total pressure values is depicted in accordance with an advantageous embodiment. Total pressure values  700  are being consolidated and are generated from total pressure values  600  in  FIG. 6 . 
     Total pressure values  700  contains total pressure for pitot-static system  702  of 24, total pressure for angle of attack system  704  of 24, and total pressure for Venturi tubes  706  of 14. The signal consolidation system generates consolidated total pressure using total pressure values  700 . The signal consolidation system may generate the consolidated total pressure by selecting the middle value from the three values. In this illustrative example, the value of 24 is selected because the highest value is 24 and the lowest value is 14. The remaining value to be selected as the middle value is 24. Thus, the signal consolidation system generates 24 as the consolidated total pressure for the aircraft. 
     In this example, Venturi tubes  706  generated a value that was ten units away from the other sensor types. The signal consolidation system may identify Venturi tubes  706  as generating inconsistent data. In some advantageous embodiments, the signal consolidation system may create a diagnostic log entry that Venturi tubes  706  generated a total pressure value that differed from the consolidated total pressure value by more than a threshold amount or percent. 
     Turning now to  FIG. 8 , an illustration of a flowchart of a process for identifying an airspeed of an aircraft is depicted in accordance with an advantageous embodiment. The process may be performed by signal consolidation system  366  running on computer system  308  in  FIG. 3 . The process may also be performed by component  502  in  FIG. 5 . 
     The process begins by generating, by a plurality of pitot-static probes, a first total pressure value and a first static pressure value for an environment surrounding the aircraft (operation  802 ). The process then generates a second total pressure value and a second static pressure value for the environment surrounding the aircraft using a plurality of light detection and ranging sensors (operation  804 ). The process then generates a third total pressure value and a third static pressure value for the environment surrounding the aircraft using a plurality of angle of attack sensor systems (operation  806 ). 
     The process then detects errors in the first total pressure value, the first static pressure value, the second total pressure value, the second static pressure value, the third total pressure value, and the third static pressure value to form a consolidated total pressure value and a consolidated static pressure value (operation  808 ). The process detects errors by selecting the middle value from the last consolidated static or total pressure value and each of the sensors of a particular type. The process then generates a consolidated static or total pressure value by taking the middle value of the remaining values. 
     Next, the process identifies an airspeed for the aircraft from the consolidated total pressure value and the consolidated static pressure value (operation  810 ). The process may identify the airspeed for the aircraft using the following formula based on Bernoulli&#39;s principle:
 
 V   c   =C   so  (5 (( P   t   −P   s )/ P   so +1) 2/7 −1)) 1/2 ,
 
where V c  is the calibrated airspeed of the aircraft, P t  is total pressure for the environment surrounding the aircraft, P s  is static pressure for the environment surrounding the aircraft, P so  is the standard day static pressure at sea-level, C so  is the speed of sound at sea-level, standard day, and V c  is the calibrated airspeed of aircraft  100 . The process terminates thereafter.
 
     Looking now to  FIG. 9 , a flowchart of [[a]] an error correction process for detecting errors is depicted in accordance with an advantageous embodiment. The process may be performed by signal consolidation system  366  by computer system  308  in  FIG. 3 . The process may also be performed by component  502  in  FIG. 5 . 
     The process begins by receiving static pressure values from each of the sensors generating static pressure values and total pressure values from each of the sensors generating total pressure values (operation  902 ). In these examples, the aircraft has at least three different sensor types and at least two of each type of sensor. The process then receives the most recent consolidated static pressure value (operation  904 ). In some advantageous embodiments, the most recent consolidated static pressure value is a value generated during operation  908  in a previous performance of the process in  FIG. 9 . Of course, if such a value is absent, a default value may be used. 
     The process then selects, for each sensor type, the middle value from the static pressure values generated by the at least two sensors of each type received in operation  904  and the last consolidated total pressure value received in operation  906  (operation  906 ). The process then selects the middle value from the values generated during operation  906  to form the consolidated static pressure value (operation  908 ). The process terminates thereafter. 
     The flowcharts and illustrations in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatus and methods in different advantageous embodiments. In this regard, each block in the flowchart or illustrations may represent a module, segment, function, and/or a portion of an operation or step. In some alternative implementations, the function or functions noted in the block may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. 
     For example, the process may generate values for the total pressure at operations  902 - 908  instead of the static pressure. Additionally, the process may store a report after operation  908  in the event that a sensor type is generating inconsistent data and/or data that differs from the values generated by the other sensor types by more than a particular amount or percent. 
     Additionally, the process may use airspeed values to detect errors instead of static pressure values in  FIG. 9 . More specifically, the process may generate a consolidated airspeed value at operations  902 - 908  instead of static pressure. 
     In such advantageous embodiments, the process may receive airspeed values instead of static pressure values at operation  902 . The proces may then receive the most recent airspeed value at operation  904  instead of the most recent static pressure value. Likewise, the process may select, for each sensor type, the middle value from the airspeed values received and the most recent airspeed value at operation  906 . Finally, the process may select the middle value from the values generated in operation  906  to form a consolidated airspeed value at operation  908 . 
     Thus, the different advantageous embodiments provide an apparatus and method for identifying an airspeed for an aircraft. In one advantageous embodiment, an apparatus is provided. The apparatus consists of a plurality of pitot-static probes. Each of the plurality of pitot-static probes is a first sensor type. The plurality of pitot-static probes generate first data. The apparatus also consists of a plurality of angle of attack sensor systems. Each of the plurality of angle of attack sensor systems is a second sensor type, and the plurality of angle of attack sensor systems generate second data. The apparatus also consist of a plurality of light detection and ranging sensors. The light detection and ranging sensors generate third data. The apparatus also consists of a signal consolidation system configured to correct errors in the first data generated by the plurality of pitot-static probes, the second data generated by the plurality of angle of attack sensor systems and the third data generated by the plurality of light detection and ranging sensors. 
     Thus, the different advantageous embodiments allow aircraft data systems and pilots to receive values for airspeed where inconsistency in the values is limited to acceptable values, even when a particular type of sensor is affected by an event, such as ice, that causes all the sensors of one type to generate inconsistent values. The aircraft data systems may exclude data from that sensor type and report that the sensor type is in need of maintenance or is not to be used until maintenance occurs. 
     Because at least three sensor types generate total and static pressure values, airspeed may be identified for the aircraft, even when all the sensors of one sensor type are generating inconsistent data. Additionally, airspeed may be identified for the aircraft, even when all of the sensors of two sensor types are generating inconsistent data because each sensor type is not affected by a particular common mode event. Additionally, the sensor type that generates the inconsistent data may be identified because two other sensor types generate consistent data and may be used to identify the airspeed of the aircraft. 
     The description of the different advantageous embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.