Patent Application
20120016539
The leading cause of worldwide aviation fatalities comes from inadvertently flying a perfectly operating aircraft into ground or water. This type of accident is referred to as Controlled Flight into Terrain (CFIT). Common causes of CFIT accidents are due to loss of radio altimeter altitude input to the enhanced ground proximity warning system (EGPWS). Altitude information from the radio altimeter (RA) is one of the critical inputs to derive the geometric altitude for EGPWS. An approach to calculation of geometric altitude is described in commonly owned U.S. Pat. No. 6,216,064.
Geometric Altitude uses an improved pressure altitude calculation, GPS Altitude, Radio Altitude, and Terrain and Runway elevation data to reduce or eliminate errors potentially induced in Corrected Barometric Altitude by temperature extremes, non-standard altitude conditions, and altimeter mis-sets. The final Geometric Altitude is computed by combining the three computed component altitudes with optional Corrected Barometric altitude. The weighting of each altitude in the final solution is based on the corresponding estimated (vertical figure of merit) VFOM. The blending algorithm gives the most weight to altitudes with a higher estimated accuracy, reducing the effect of less accurate altitudes on the final computed altitude. Each component altitude is also checked for reasonableness using a window monitor computed from GPS Altitude and GPS VFOM. Altitudes that are invalid, not available, or fall outside the reasonableness window are not included in the final blended altitude.
Radio Altitude Calibrated Altitude is a calibration of Non-Standard Altitude during approach using an altitude derived from radio altitude (height above terrain) and the terrain elevation data stored in the EGPWS terrain database. This calibration is performed during the approach phase of flight when the aircraft is within a minimum distance and elevation of any runway. Once a correction factor is determined, it is applied to Non-Standard Altitude (or Standard Altitude) until the aircraft lands.
In the event of RA failure, or failure of any other instrument providing altitude information, the determination of geometric altitude is severely compromised.
In an embodiment, a system includes a memory device, and a processor coupled to the memory device. The processor is configured to receive, in a first time interval, from a first component a signal indicating an altitude of the aircraft, from a second component a signal indicating a first heading of the aircraft, and from a third component a signal indicating a first position of the aircraft. The processor is further configured to receive, in a second time interval later than the first time interval, and from the second and third components, signals respectively indicating a second heading and second position of the aircraft. The processor does not receive a signal from the first component in the second time interval. The processor is further configured to determine an estimated altitude of the aircraft and a geometric altitude of the aircraft.
Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings.
An embodiment of the invention is directed towards prediction of the aircraft altitude in the event of failure of RA, or loss of altitude information from any other sensor, serving as input to calculate the Geometric Altitude for EGPWS using the blending algorithm and continue providing this information to EGPWS until VFR (visual flight rules) condition is reached during the approach phase and until the operational range limit of the RA during climb-out phases of flight is reached.
An embodiment of the invention is directed towards an Altitude Prediction approach for estimating and predicting the aircraft altitude to the TA&D function of the EGPWS by maintaining the integrity of the existing blending algorithm to calculate the Geometric Altitude for the EGPWS. Unlike conventional approaches, an embodiment accrues and stores the predicted altitude information. This altitude data is ‘volumetric’ or ‘three-dimensional,’ because it is built from and constantly updated by systematic calculation of predicted height information in the area in front of the airplane over the flight path angle.
An embodiment of the invention computationally “builds” the equivalent of a cuboid in space in front of the airplane. The present position of the aircraft is stored in a 3-D buffer, so that this information can be used to calculate the predicted position over a range of two voxels, for example, apart along the flight path angle. The predicted positions/altitude information are stored in the 3-D buffer continuously. In the event of system failure of Radio Altimeter or any other sensor input to the blending algorithm, the information is extracted from this buffer and replenished as an input to computation of RA Calibrated Altitude, or similar corresponding input. The altitude information stored in the buffer is not only extracted and provided to EGPWS but also may be used to calculate the subsequent altitude information/aircraft position with respect to the cells in the buffer based on the flight path angle with a high degree of accuracy. During the critical approach phase this information continues to be provided to the EGPWS until the Decision height or conditions for a VFR approach is reached.
An embodiment of the invention can be yet another mode of EGPWS. For example, the activation of this mode can be based on the RA failure (or any other sensor failure). The EGPWS can indicate this failure with the usual RED indicator lamp. There could be the sounding of a caution alarm as “Radio Altimeter failure” (or any other corresponding sensor failure) so that the pilot remains in auto-pilot mode or can stay on the flight plan course with as little deviation as possible. Such would result in accurate prediction of RA information from the 3-D Buffer prediction approach discussed herein. However, if there is still a deviation in the flight course from the stored flight plan, the heading information from an inertial navigation system (INS) could be used, as well.
Embodiments of the invention may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer and/or by computer-readable media on which such instructions or modules can be stored. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.
According to one or more embodiments, the combination of software or computer-executable instructions with a computer-readable medium results in the creation of a machine or apparatus. Similarly, the execution of software or computer-executable instructions by a processing device results in the creation of a machine or apparatus, which may be distinguishable from the processing device, itself, according to an embodiment.
Correspondingly, it is to be understood that a computer-readable medium is transformed by storing software or computer-executable instructions thereon. Likewise, a processing device is transformed in the course of executing software or computer-executable instructions. Additionally, it is to be understood that a first set of data input to a processing device during, or otherwise in association with, the execution of software or computer-executable instructions by the processing device is transformed into a second set of data as a consequence of such execution. This second data set may subsequently be stored, displayed, or otherwise communicated. Such transformation, alluded to in each of the above examples, may be a consequence of, or otherwise involve, the physical alteration of portions of a computer-readable medium. Such transformation, alluded to in each of the above examples, may also be a consequence of, or otherwise involve, the physical alteration of, for example, the states of registers and/or counters associated with a processing device during execution of software or computer-executable instructions by the processing device.
The operating environment illustrated in
The alerting algorithm component 522 determines if the airplane is predicted to encroach on any protected airspace volume. The EGPWS 510 includes an aural message generator that provides audible information to the pilot after the alerting algorithm component 522 determined that there is imminent conflict with a protected airspace. The maneuvering algorithm component 524 generates guidance commands for output to the pilot or an automatic flight control system 540 for avoiding the protected airspace.
Each voxel 550 is a perfect cube. The x and y planes are 128 voxels 550 in length, in an embodiment, although more or fewer such voxels may be used, as appropriate. The division of 64 feet, in an embodiment, by 128 voxels provides a voxel size of 0.5 feet in the x and y planes. Consequently, each voxel 550 is 0.5 feet in length in the z plane. In the illustrated embodiment, 128 layers of voxels 550 are included in the z plane. As discussed in further detail below, this 3-dimensional cuboid 555 is continuously logically “moved” correspondingly to movement of the aircraft.
The dimensions of the voxels 550 can be altered as per the size of the cell of the digital terrain elevation database stored in EGPWS, provided sufficient accuracy as that of RA is still achieved.
Referring to
At a block 220, EGPWS 510 receives heading information, including ascent/descent angle, from system 534. As above alluded to, if the aircraft is on the flight plan course, data from a flight management system (FMS) may be used. Otherwise, the heading information supplied by an INS may be used.
At a block 230, EGPWS 510 receives aircraft position data, including aircraft longitude/latitude, from system 530.
At a block 240, the data received in blocks 210-230 is used to initialize or update, as appropriate, a reference point defining the current position of the aircraft relative to previously determined aircraft positions and predicted aircraft positions as stored in the 3-D buffer 511.
As discussed above, the cuboid 555 generated by buffer 511 is considered to be dynamically moving along with the motion of the aircraft at all times in accordance with motion-compensation techniques. To perform motion compensation accurately, the total aircraft displacement from a chosen frame of reference should be tracked constantly, including during turn-around times. The inputs to aircraft position integration may be heading (radians), drift angle (radians), delta time to the last reported aircraft position (seconds), ground speed (meters/second), and data indicating previous aircraft position (reference point).
Aircraft position integration may be initialized by “marking” the position of the aircraft by initializing an object called a reference point. Reference points accumulate as the aircraft moves from the position at which the reference points were initialized. Reference points track Δx displacement (left/right), Δy displacement (forward/rear), and record the aircraft heading (radians) at the time of initialization. The output of the aircraft position integration may be Δx—relative displacement of aircraft (left/right), Δy—relative displacement of aircraft (forward/back), Δh—relative difference in heading (radians), and an updated reference point containing the updated Δx and Δy.
Referring now to
For example, Y1, Y2, Y3, Y4, Y5 may represent successive predicted positions of the aircraft populating corresponding alternate cells (e.g., 2 voxels away from a prior estimated position) of the cuboid 555. These predicted heights may be calculated using the current position “X” determined with reference to the cuboid 555. The following equations provide a first estimated height “Y1,” a second estimated height “Y2,” etc. Note that these predicted heights may be a function of Δx, Δy and Δh as determined using the above-described motion-compensation techniques:
Y1=X±(Z±Δy) tan ({acute over (α)}±Δh),
Y2=Y1±(Z±Δy) tan ({acute over (α)}±Δh),
Y3=Y2±(Z±Δy) tan ({acute over (α)}±Δh),
Y4=Y3±(Z±Δy) tan ({acute over (α)}±Δh),
Y5=Y4±(Z±Δy) tan ({acute over (α)}±Δh),
where, Z is the distance, in an embodiment, two cells away from the current aircraft position along the flight path angle {acute over (α)}.
At a block 260, EGPWS 510 determines whether data is available from the RA (or other applicable altitude sensor). If such data is available, then the process 200 moves to block 290. Otherwise, the process moves to block 270.
At block 270, EGPWS 510 determines predicted radio altitude calibrated altitudes (RACAs) for use in determining predicted geometric altitudes of the aircraft. The RACAs may be determined by correlating the GPS position of the aircraft with the predicted heights stored in 3-D buffer 511, accessing terrain elevation data stored in the Terrain Database and correlated with the GPS position, and adding the terrain elevation data to the stored predicted heights.
Referring now to
At block 290, EGPWS 510 determines whether the aircraft is in the approach/landing phase of flight. If the aircraft is in the approach/landing phase of flight, then the process 200 moves to block 300. Otherwise, the process 200 moves back to block 210.
At block 300, EGPWS 510 determines whether the most-extended predicted height (e.g., Y5) is associated with a voxel of a layer in the 3-D buffer 511 corresponding to a decision height for VFR conditions. If so, then the process 200 ends. Otherwise, the process 200 moves back to block 210.
While a 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.
