Patent Application
20070010921
Development of ground proximity warning systems has advanced safety in aircraft flight. The flight parameters of the aircraft and the terrain surrounding the aircraft trigger alerts to the flight crew given a likelihood of collision with either terrain or other obstacles. In spite of the utility of in-flight warnings, the utility of these systems must be balanced against diverting attention of the flight crew with false alerts, ultimately training the flight crew to ignore alarms from the ground proximity warning system altogether.
In landing, ground proximity warning systems, if not adequately controlled, may generate unwanted alarms as the aircraft nears the earth. Undue or nuisance alarms during landing are a distraction and contribute to stress attendant to a successful landing. Additionally, the nuisance alarms may distract from critical alarms sounding in the cockpit.
Ground proximity warning systems have been developed that evaluate the proximity of the aircraft to an airport and the flight altitude of the aircraft above the runway to determine if the aircraft is entering a landing procedure. For example, one ground proximity warning system monitors the altitude of the aircraft in relation to the runway closest to the aircraft. If the aircraft approaches the runway within a predetermined distance range and within a predetermined altitude range, the ground proximity warning system will determine that the aircraft is entering a landing procedure. Selection of a runway according to a glide slope angle is discussed in detail in U.S. Pat. No. 6,304,800, entitled “Methods, Apparatus And Computer Program Products For Automated Runway Selection” which is assigned to the assignee of the present application. The teaching of U.S. Pat. No. 6,304,800 is incorporated herein by reference.
With reference to
To determine an acceptable altitude and distance throughout the course of the landing maneuver, a ground proximity warning system defines the approach envelope 66 detailing altitude and distance parameters defining positions suitable for the aircraft 62 as the aircraft lands on the candidate runway 64. The approach envelope 66 includes an outer distance boundary 68 that defines the maximum distance that the aircraft 62 can be from the candidate runway before the candidate runway will be considered, shown in nonlimiting example as five nautical miles. The outer distance boundary 68 is typically chosen based on the need to provide adequate alarm protection, while at the same time reduce the number of nuisance alarms generated.
The approach envelope 66 also includes an upper altitude boundary 70. The upper altitude boundary 70 defines the maximum altitude that the aircraft 62 can be above the candidate runway 64 and the candidate runway 64 still be considered as the candidate runway 64.
Within the outer distance boundary 68 and upper altitude boundary 70, the approach envelope 66 further includes an upper landing envelope ceiling 72. The upper landing envelope ceiling 72 is considered to be at too high an altitude above the candidate runway 64 in relation to the distance the aircraft 62 is from the candidate runway 64. The upper landing envelope ceiling 72 is typically defined with respect to a lower glide slope angle 86 multiplied by the distance the aircraft 62 is from the candidate runway 64 (i.e., Predefined Altitude Distance to Runway), and in typical embodiments, the predefined altitude is 700 ft./nautical mile. The 700 ft predefined altitude is a nonlimiting example but is chosen as it represents the upper glide slope angle of 7 degrees consistent with performance typical of commercial aircraft.
Customarily, when within a designatable proximity to the candidate runway 64, the upper landing envelope ceiling 72 is defined to include a flat or 0 degree slope portion 76. In recognition that runway elevation errors or height errors may tend to cause the aircraft 62 to be flying a constant height over the runway 64 rather than on it, the appropriate envelope 66 allows for such errors without sounding an alert. The flat angle approach is used as a non-limiting example of a configurable lower limit. Additionally the aircraft 62 may be engaged in a circling pattern before landing on the runway 64.
Additionally, the approach angle envelope 66 also includes a lower landing envelope floor 78. The lower landing envelope floor 78 includes first and second floor threshold functions, 80 and 82, respectively. The first portion of the floor threshold 80 of the landing envelope floor 78 meets a lower glide slope angle 86 projection. An aircraft 62 in a region 84 below the landing envelope floor 78 is considered to have too low an altitude for the distance between the aircraft 62 and the candidate runway 64 for the aircraft 62 to be landing on the runway 64. Similar to the upper ceiling 72, the slope of the first portion of the landing envelope floor 78 is typically based on a predefined altitude multiplied by the distance the aircraft is from the runway.
Use of the closest runway to the aircraft 62, however, is not always an optimal solution where several runways are geographically close to one another when the aircraft 62 approaches the airport from one direction with intentions of landing on a runway on the opposite side of the airport. In these instances, the ground proximity warning system prematurely disables or desensitizes the alarms. Where two airports at different elevations above sea level are located in close proximity to one another, and the aircraft 62 flies near one airport at low altitude in route to the second airport, the ground proximity warning system will use the closest runway of the first airport in the creation of the terrain floor. Based on the distance from the closest runway, the ground proximity warning system will generate terrain caution or terrain warning alerts based upon the incorrect assumption that the aircraft 62 is landing at the first airport.
While commercial aviation generally uses a 3 degree glide path as the regular approach for landing, such aviation is not constrained to do so and may use a glide slope as little as 0 degrees to as much as 7 degrees. Topography proximate to the airport often dictates the most advantageous glide slope angle. Known ground proximity warning systems have no means by which to differentiate between landing on smooth unobstructed terrain and more challenging approaches.
What is needed in the art is a ground proximity warning apparatus with a facility to predict a more likely runway from among several candidate runways based upon data stored in association with each of the candidate runways.
An apparatus, method and database for predicting which one of at least two candidate runways on which an aircraft is most likely to land includes a database. The database is configured to contain at least two runway data. The runway data includes an empirical glide slope angle and a location associated with each candidate runway. A position sensor is configured to determine a position of the aircraft. A processor is configured to retrieve the glide slope angle and location data associated with each of the at least two candidate runways. The processor calculates an aircraft glide slope angle relative to each of the at least two candidate runways based upon the position of the aircraft, and derives a first likelihood for each of the at least two candidate runways based upon the empirical glide slope angle and the aircraft glide slope angle associated with the runway.
In accord with further embodiments, the database includes runway data stored in association with each of a plurality of runways. The runway data includes a location datum. The location datum is configured to fix the runway in a spherical coordinate system. The runway data also includes an empirical glide slope angle. The empirical glide slope angle selected to represent a most likely glide slope to approach the runway.
As will be readily appreciated from the foregoing summary, the processor orders candidate runways based upon an empirical probability model based upon the glide slope angle. A likelihood of landing value is ascribed to each of the candidate runways based upon an aircraft position and the empirical probability model. The likelihood of landing value is then used by the processor to order the runways and select a most likely runway.
The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings.
With relation to the description of the various embodiments provided in detail below, it must be understood that the present invention can be used with any system that uses information concerning runways for system calculations. Referring now to
With reference to
The look-ahead warning generator 14, bases the approach envelope on altitude data from the altitude sensor 18, position data from the position sensor 16, a heading from the heading sensor 22, and optionally, from the track data from a track sensor 21, and a ground speed of the aircraft derived from the position sensor and, again, optionally from an airspeed sensor 20. The position sensor may include a global positioning system (GPS), inertial navigation system (INS), or a flight management system (FMS). The look-ahead warning generator 14 also receives altitude and airspeed data from the altitude sensor 18 and the airspeed sensor 20, respectively, and the aircraft track and heading information from track and heading 21, 22 sensors, respectively. In addition to receiving data concerning the aircraft 62, the look-ahead warning system also receives data concerning the terrain surrounding the aircraft. Specifically, the look-ahead warning generator 14 is also connected to the memory device 24 that contains a searchable database of data relating, among other things, to the position and elevation of various terrain features and elevation, position, and quality information concerning runways.
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Ground proximity warning systems that typically select the candidate runway 64 closest to the aircraft 62 may generate a look-ahead envelope 66 (
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Like the bearing deviation angles 36, 38, the track deviation angles 44, 50 include information assistive in predicting the runway on which the aircraft 30 is most likely to land. In addition, like the bearing deviation angles 36, 38, selecting the angle of lesser magnitude is likely but not conclusive on predicting the runway on which the aircraft is most likely to land. The aircraft 30 may, from time to time turn on approach which, for instance in the course of a “carrier turn” prior to landing, the track deviation angle 44, 50 is constantly reducing until the aviator has aligned the aircraft 30 with the runway prior to landing.
Typically, when landing the aircraft 30 according to a safe final approach to the runway 54, the glide slope deviation angle 58 will fall within a predetermined range of vertical angles. For commercial aircraft, the glide slope deviation angle 58 will fall within a range of about 0 degrees to about +7 degrees. Glide slope deviation angles 58 outside of the range unduly stress the aircraft 30 as it maneuvers into a safe glide slope. The approach envelope 66 (
An embodiment of the invention includes the ascertaining and predicting of suitable approaches according to a particular candidate runway. Where terrain; prevailing weather; or other obstacle makes either a steeper or a shallower slope a more appropriate glide slope deviation angle than a default glide slope deviation, a modifying glide slope deviation angle is retrieved in association with the candidate runway 54. A means of developing such a stored glide slope deviation angle is through empirical collection of angles selected by pilots landing at a designated runway.
In the embodiment portrayed at
Each stored glide slope angle 86 is the angle associated with each of the candidate runways. Such glide slope angles 86 may be derived to be an empirical angle or it may be a default angle of three degrees to horizontal. The empirical angle is, as suggested, an angle that is arrived at by observation of landings on the runway and may optionally include an averaging constant to adjust the glide slope angle according to repeated observations of glide slope angles when landing on the runway in question. The glide slope angle is observed and compared to that which is then retrieved due to association with the runway to which the aircraft is proximate. The retrieved value is used to decide the appropriate runway from among the candidate runways 64. Upon landing on one of the candidate runways, the processor 12 will ascribe the glide slope angle observed to the runway upon which the pilot landed the aircraft 62 and will suitably average the observed glide slope angle with the stored glide slope angle 86 associated with this candidate runway 64, optionally using the averaging constant, and store the result to replace the stored glide slope angle 86 associated with the candidate runway 64 to further refine the value of the stored glide slope angle 86.
Alternatively, an angle for suitable approach to a runway may be defined by an Instrument Landing System (“ILS”) in place for that runway. An approach using ILS is generally known as an instrument approach and generally is used where visual cues are not present to the pilot because such are obscured by weather or lighting. An instrument approach is an approach where radio transmitters give the pilot of an aircraft visual cues generated on the face of an aircraft's instruments. If the pilot follows these generated visual cues, the aircraft will arrive near the approach end of the runway, usually 200 feet above the surface. The selected angle for instrument approaches is the same angle that, in this embodiment, is used as the recalled stored glide slope angle 86 associated with this candidate runway 64. The highest likelihood of landing, then, is according to the instrument landing approach as the ILS system defines it. Therefore where an ILS angle is available, an embodiment defaults to recalling that angle in favor of deriving an empirical angle.
Referring to
The probability function of the bearing deviation angle has a maximum likelihood arbitrarily set at a value of one to represent a maximum likelihood of landing on the candidate runway 32, 34. The maximum value is found at zero degrees to represent alignment on an instantaneous horizontal path 31 with the centerline of the runway. In general practice, such alignment is indicative of an intent to land on the runway with which the aircraft 30 is aligned. From the value of one, the magnitude of the function and thus the function curve 87 falls off gradually as the deviation angle bearing reaches the conventional maximum for generally acceptable commercial practices (the operational region 88). At the point of the conventional maximum bearing deviation angle for generally acceptable commercial practices, the likelihood is set at a second arbitrary value indicative of a lesser likelihood, proportionally lesser in magnitude than the likelihood of landing on a runway with which the aircraft is suitably aligned.
The function curve 87 moves to the transition region 89 at the conventional maximum deviation angle for generally acceptable commercial practices, and falls off as the deviation angle increases to the functional maximum deviation angle for the aircraft 30. From the functional maximum deviation angle to 180 degrees, the likelihood of landing is represented as zero in the non-operational region 90.
Similarly, referring to
Within the landing operational region 92, likelihood of landing on the candidate runway declines from a maximum value, arbitrarily set at a value of one where, as with predicting a candidate runway based upon the bearing deviation angle, where the instantaneous horizontal path 31 of the aircraft 30 aligns with a centerline of a candidate runway 40, 42 or at zero degrees. From the maximum value of one at zero degrees, the likelihood of the aircraft 30 landing on the candidate runway drops relatively rapidly to a value of zero at the operational maximum track deviation angle 44, 50. In the oblique region 93, the track deviation angle 44, 50 exceeds the operational limits of the aircraft 30 and thus, the likelihood of landing on the candidate runway 40, 42 and likewise the likelihood function curve 91 remains at the value zero throughout the oblique region 93.
The takeoff operational region 94 is used to increase rather than to decrease the floor threshold 80 (
Referring to
Allowing the point of maximum likelihood 101 to vary from three degrees allows the selection of the candidate runway where terrain surrounding the candidate runway forces either a steeper or shallower approach than the typical three degree approach.
Within the steep approach region 96, the likelihood function curve 95 drops off to a point that is defined by the operational limits of the aircraft 30. At the operational limit of the aircraft 30, the likelihood function curve 95 drops to a value of zero in the flyover region 99 reflecting the inability of the aircraft 30 to safely land according to an approach angle of magnitude within the flyover region 99.
In the level flight region 96, where the aircraft is at a same altitude or just slightly above the altitude of the candidate runway such that glide slope deviation angle 58 has a magnitude of between zero and one-half of a degree, the glide slope deviation angle 58 is measured as the deviation from the horizontal from a point at end of a runway. The likelihood is assigned a constant value of, in this nonlimiting example, one to indicate that, in commercial practice, an aircraft has a set likelihood of landing and, therefore, the likelihood function curve 95 remains at a lower likelihood in the level flight region 96.
From just below one-half degree to the point of maximum likelihood 101, the likelihood function curve 95 shows an increasing likelihood as the glide slope deviation angle 58 increases to the point of maximum likelihood 101. Again, the value assigned to a peak value of 1.1 in this nonlimiting example is an arbitrary one reflecting a statistically higher likelihood at the point of maximum likelihood 101.
Referring as well to
Based upon a position of the aircraft 30, the processor 12 retrieves from the memory device 24, all data relating to each candidate runway 54 within a designatable radius of the aircraft 30 position, at a block 110. Each of the candidate runways 54 are associated with unique data including an empirical glide slope deviation angle 58 stored in the memory device 24.
The data associations for each candidate runway 54 within the designatable radius are used to determine the glide slope deviation angle 58 corresponding to each candidate runway 54, at a block 120. At a block 130, the processor 12 derives a value of the likelihood of landing function curve 95 associated with the candidate runway 54 at each measured glide slope deviation angle 58 associated with each candidate runway 54. The processor 12 selects the candidate runway associated with the greatest of the derived likelihood of landing values as the predicted runway at a block 140.
Because each of the likelihood function curves 95 used by the processor 12 is unique and associated with the candidate runway 54, the likelihood value derived, even from similar glide slope deviation angles 58 may be very different. Thus, where a first candidate runway 54 having obstructing terrain preventing a three-degree approach has a four-degree point of maximum likelihood 101, the processor 12 is more likely to predict a second candidate runway 54 at an equal altitude where no obstructing terrain exists.
Referring to
While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.
