The present invention relates generally to ground proximity warning systems for use in aircraft. More particularly, the apparatus, methods, and computer program products of the present invention relate to determining a corrected distance between an aircraft and a selected runway to thereby account for the altitude of the aircraft above the selected runway as the aircraft approaches the runway.
An important advancement in aircraft flight safety has been the development of ground proximity warning systems. These warning systems analyze the flight parameters of the aircraft and the terrain surrounding the aircraft. Based on this analysis, these warning systems provide alerts to the flight crew concerning possible inadvertent collisions with terrain or other obstacles.
Two important aspects of ground proximity warning systems are the need to operate independent of user input and the need to reduce the number of nuisance alarms provided to the flight crew. In light of this, at least one ground proximity warning system has been developed that, for the most part, operates independent of user input and provides mechanisms to reduce the number of nuisance alarms published to the flight crew.
Specifically, to operate independent of user input, this ground proximity warning system continuingly selects a runway that is near the current position of the aircraft. The global coordinates and elevation of the selected runway are used by the ground proximity warning system for ground proximity warning calculations. For instance, the ground proximity warning system uses the flight parameters of the aircraft, such as the position, altitude, ground speed, track and heading of the aircraft, and the global coordinates and elevation of the selected runway to construct terrain clearance floor envelopes about the aircraft. Based on these terrain clearance floor envelopes, the ground proximity warning system provides alarms to the flight crew of any impending intersection of the flight path with terrain or obstacles.
In addition to aiding in the generation of terrain clearance floor envelopes independent of user input, the selected runway is also used to reduce the number of nuisance alarms generated. Specifically, the ground proximity warning system alters the terrain clearance floor envelopes based on the distance between the aircraft and selected runway to prevent the occurrence of nuisance alarms. As the aircraft approaches the selected runway, the terrain clearance floor envelopes are typically altered to reflect a landing approach pattern for the aircraft. Alteration of the terrain clearance floor envelopes based on a landing pattern reduces the number of nuisance alarms generated.
The ground proximity warning system also uses a restricted look ahead distance to reduce the occurrence of nuisance alarms. The restricted look ahead distance represents a distance ahead of the aircraft in which the ground proximity warning system will provide warnings to the flight crew. By restricting the distance in front of the aircraft for which alarms are generated, the number of nuisance alarms is reduced.
The number of nuisance alarms is also reduced by basing the value of the look ahead distance as a function of the distance between the aircraft and the selected runway. As an aircraft approaches a runway for landing, the ground proximity warning system reduces the value of the look ahead distance based on the proximity of the aircraft to the selected runway. Specifically, as illustrated in FIG. 1, the ground proximity warning system typically uses the coordinate distance 14 between the aircraft 10 and selected runway 12 for ground proximity warning calculations. With reference to FIG. 2, the ground proximity warning system determines the look ahead distance value by comparing a distance between the aircraft and selected runway to a look ahead distance equation, such as the equation depicted graphically in FIG. 2:
LADDist. to Runway=(3.25/6)(Distance to Runway)xe2x88x920.3333,
for look ahead distance (LAD) values between 0.75 nmxe2x89xa6LADxe2x89xa64 nn corresponding to distances between the aircraft and runway of 2 to 8 nm. The look ahead distance equation is designed to reduce the look ahead distance of the ground proximity warning system as the aircraft approaches the runway to thereby reduce nuisance alarms.
While the use of a selected runway for terrain clearance floor envelopes and look ahead distance calculations is advantageous as it allows the ground proximity system to operate independent of the user input, there are some drawbacks. Specifically, because the ground proximity warning system does not receive user input concerning the destination of the aircraft, as the aircraft approaches the selected runway, the terrain clearance floor envelopes and look ahead distance value are typically reduced as though the aircraft is landing on the selected runway. Although reduction of the look ahead distance value and terrain clearance floor envelopes is advantageous for reducing nuisance alarms when the aircraft is actually landing on the runway, it may be less advantageous when the aircraft is merely flying near the runway en route to another destination.
To address this problem, the conventional ground proximity warning system typically places a lower limit on the look ahead distance value, if the aircraft has an altitude with respect to the runway that is greater than a predetermined altitude. For example, if the altitude of the aircraft above the runway is greater than 3500 ft, the ground proximity warning system may limit the look ahead distance value (LADDist. to Runway) to a minimum value of, for example, 2.375 nm. As such, as the aircraft approaches the selected runway, the look ahead distance value will be reduced by the equation depicted graphically in FIG. 2 until the look ahead distance value is equal to the minimum look ahead distance value, i.e., 2.375 nm, at which point the look ahead distance value is no longer reduced, as depicted in dashed lines.
Although limiting the look ahead distance value to a minimum value based on the altitude of the aircraft above the runway is advantageous, there are some drawbacks to this approach. Specifically, the conventional ground proximity system does not adjust the minimum look ahead distance value for an aircraft that has an altitude with respect to the runway that is significantly higher than the predetermined altitude. For example, if the predetermined altitude is 3500 ft, an aircraft that is 20,000 ft above the selected runway will have the same minimum look ahead distance value as if the aircraft is 3500 ft above the selected runway. In light of this, a ground proximity warning system that accounts for the altitude of the aircraft above the selected runway in determining a distance between the aircraft and selected runway for ground proximity warning calculations would be desirable.
As set forth below, the apparatus, methods, and computer program products of the present invention may overcome many of the deficiencies identified with the use of the distance between an aircraft and selected runway for ground proximity warning calculations. The present invention provides several apparatus, methods, and computer program products for determining a corrected distance between an aircraft and a selected runway. Specifically, the present invention selects either the coordinate distance between the aircraft and the selected runway or a calculated distance value as the corrected distance value for ground proximity warning calculations. The calculated distance value is a distance value calculated based on a mathematical relationship between the altitude of the aircraft and a predetermined glideslope. The predetermined glideslope value is a maximum glideslope, above which, the aircraft is most likely not landing on the selected runway. The determination of the corrected distance between the aircraft and selected runway is therefore based on the aircraft""s altitude and position with respect predefined glideslope.
Specifically, the predetermined glideslope defines a glideslope angle above which the aircraft is most likely not landing on the runway. If the altitude and distance of the aircraft is such that the aircraft has a glideslope angle with respect to the runway that exceeds the predetermined glideslope value, it is assumed that the aircraft is not landing on the selected runway. In this instance, the apparatus, methods, and computer program products select the calculated distance value, as opposed to the coordinate distance value for ground proximity warning calculations.
By selecting a corrected distance value based on the distance and altitude between the aircraft and runway and the predetermined glideslope, the present invention can alleviate some of the problems associated with using a selected runway for ground proximity warning calculations. Specifically, if the aircraft is positioned in relation to the selected runway such that it is unlikely that the aircraft is landing on the runway, the present invention selects a calculated distance value for use in the ground proximity warning calculations. This may be advantageous as the calculated distance value accounts for the altitude of the aircraft in relation to a predetermined glideslope.
The present invention provides several embodiments for determining a corrected distance between an aircraft and a selected runway. For example, one embodiment of the present invention provides an apparatus and method for determining a corrected distance between an aircraft and a selected runway based on an altitude and distance of the aircraft from the selected runway. The apparatus of this embodiment includes a processor. In operation, the processor compares the coordinate distance between the aircraft and selected runway and a calculated distance value calculated based on the altitude of the aircraft above the runway and a predetermined glideslope. The processor selects either the coordinate distance or the calculated distance value as the corrected distance between the aircraft and the selected runway based on a mathematical relationship between the coordinate and calculated distance values. For instance, in one embodiment, the processor compares the coordinate and calculated distance values and selects the larger of the values as the corrected distance between the aircraft and the selected runway.
As discussed above, the predetermined glideslope value defines a predefined relationship between altitude and distance to the selected runway. In one embodiment, the predetermined glideslope value is expressed by the equation:
X=(Y/tan xcex8)
where
xcex8=predetermined glideslope angle,
Y=altitude above the runway in ft, and
X=calculated distance value in ft.
In this embodiment of the present invention, the processor determines the calculated distance value based on this equation. The processor next compares the coordinate distance between the aircraft and the selected runway to the calculated distance value. If the calculated distance value exceeds the coordinate distance value, the processor determines that the aircraft has a glideslope angle with respect to the runway that exceeds the predetermined glideslope value. In this instance, the processor selects the calculated distance as the corrected distance to runway value. Likewise, if the calculated distance value is less than the coordinate distance value, the processor determines that the aircraft has a glideslope angle with respect to the runway that is less than the predetermined glideslope value. In this instance, the processor selects the coordinate distance as the corrected distance to runway value.
The present invention also provides computer program products for determining a corrected distance between an aircraft and a selected runway based on an altitude and distance of the aircraft from the selected runway. The computer program products include a computer readable storage medium having computer readable program code means embodied in the medium. The computer-readable program code means includes first computer instruction means for comparing a coordinate distance value representing a distance between the global coordinate values of the aircraft and the global coordinate values of the selected runway to a calculated distance value calculated based on the altitude of the aircraft above the runway and a predetermined glideslope. The computer-readable program code means also includes second computer instruction means for selecting one of the coordinate distance value and the calculated distance value as the corrected distance between the aircraft and the selected runway based on a mathematical relationship between the coordinate and calculated distance values.
The present invention also provides an apparatus and method for determining a corrected distance between an aircraft and a selected runway based on the position of the aircraft with respect to an envelope constructed about the selected runway, where the envelope represents a predetermined glideslope angle. In this embodiment of the present, the processor evaluates the altitude and distance between the aircraft and the selected runway with relation to the envelope constructed about the runway. If the aircraft is within the envelope, the processor selects the coordinate distance value representing a distance between the aircraft and the selected runway. However, if the aircraft is outside of the envelope, the processor selects a calculated distance value calculated based on the altitude of the aircraft above the runway and the predetermined glideslope.
Specifically, in one embodiment of the present invention, to determine whether the aircraft is inside the envelope constructed about the runway, the processor compares the coordinate and calculated distance values to each other. If the coordinate distance value is larger than the calculated distance value, the aircraft is inside the envelope. In this instance, the processor selects the coordinate distance as the corrected distance value used for ground proximity warning calculations. However, if the coordinate distance value is less than the calculated distance value, the aircraft is outside the envelope, and the processor selects the calculated distance as the corrected distance value.
Selection of the calculated distance value for ground proximity warning calculations when the aircraft is outside of the predefined envelope is typically advantageous. Specifically, the calculated distance value accounts for the altitude of the aircraft above the selected runway. Further, as the aircraft approaches the runway at a given altitude, the calculated distance value will correspond to a distance to runway value at the given altitude along the predefined envelope, while the actual distance value between the aircraft and selected runway will decrease. When the aircraft exceeds the predefined glideslope, the calculated distance value will correspond to a larger look ahead distance value than the actual distance value. As such, if the aircraft exceeds the predefined envelope, a larger look ahead distance value will be used for ground proximity warning calculations.
In addition to determining a corrected distance between the aircraft and a selected runway, the present invention also includes apparatus and methods for determining a look ahead distance value. In this embodiment, the processor compares the corrected distance value to a ground speed look ahead distance value and a roll angle look ahead distance value. In this embodiment, the ground speed look ahead distance value is based upon the ground speed of the aircraft and an assumed turning radius of the aircraft, and the roll angle look ahead distance value is based upon the roll angle of the aircraft and an actual turning radius of the aircraft. Based on this comparison, the processor selects one of the look ahead distances for use in ground proximity warning calculations. Specifically, in one embodiment, the processor selects the smaller of the calculated distance value, ground speed look ahead distance value, and the roll angle look ahead distance value as the look ahead distance value. The smaller of the look ahead distance values is typically selected to provide the most conservative look ahead distance to thereby reduce instances of nuisance alarms.