Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
1998-12-22
2001-01-23
Tarcza, Thomas H. (Department: 3662)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C342S033000, C342S357490, C342S357490
Reexamination Certificate
active
06178363
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for providing precision information for airplanes during initial and terminal phases of flight, and more specifically, methods and apparatus for performing precision guidance using a global positioning system, and an inertial reference system.
BACKGROUND OF THE INVENTION
As will be understood from the following description, the present invention was developed for increasing the availability of precision approach landings using a Global Positioning System (GPS) Landing System (GLS) and an Inertial Reference System (IRS) at airports anywhere in the world.
The Automatic Landing Systems (i.e., autopilots) on today's commercial airplanes receive their guidance from a ground-based Instrument Landing System (ILS). In low weather minimums, the integrity and continuity of the ILS transmissions are absolutely crucial to the safety of the airplane during the final phase of approach, touchdown and roll-out. (“Integrity” is the probability that the signals are not hazardously misleading. “Continuity” is the probability that the signals remain present and usable during the approach). The integrity is assured by a set of near-field and far-field monitors, ready to shut down the ILS should the ILS signals move outside allowed tolerances. The continuity of the signals is assured by a backup transmitter. The backup transmitter comes on-line if the primary transmitter fails or is shut down. A key feature of today's systems is that the ground station has the sole responsibility for ensuring the integrity and continuity of its own transmissions. Because ILS equipment is costly due to initial purchase price and maintenance costs, ILSs are only practical at airfields that have large incomes generated by commercial traffic or government funding. Also, ILS signals are sensitive to local building construction and even vehicle movement. This sensitivity increases operating costs, because the ILS operators, such as the Federal Aviation Administration (FAA) in the US, must continually ensure each ILS is producing an accurate signal. Therefore, global implementation is not practical.
The GLS has been proposed as a replacement for ILS. GLS is attractive, because satellite signals are present everywhere in the world, at no cost to airports or other authorities responsible for providing airplane approach information.
In present GLSs, airplane position signals, determined from GPS signals sent by orbiting satellites, are augmented in the airplane by differential corrections (differential GPS) received from a local ground station. The differentially corrected GPS signals are referenced to an intended approach path received by the airplane from the same ground station. The ground station is also responsible for monitoring each satellite and providing airplanes with the integrity status of each satellite. The integrity and continuity of the received airplane position signals depend on the number of satellites in the airplane's field of view, the satellites' positions in the sky (their “geometry”), and the data received from the ground station. The airplane's on-board equipment must determine that the signals being received from satellites and ground station will provide a level of integrity and continuity compatible with the prevailing approach weather minimum for the duration of the approach about to be performed. There will be times and places in the world where the satellites in view cannot support the required continuity and integrity for certain approaches, such as FAA Category 3 (Cat. 3) approaches.
Even when the satellite geometry supports the required continuity and integrity, the signals received by airplanes are subject to environmental threats, such as electromagnetic interference (EMI) (both accidental and malicious), lightning and ionospheric scintillation (i.e., brown-outs associated with sunspot activity). There is also the threat of random satellite failures and satellites setting over the horizon. These threats can affect the reception of some or all of the available satellite signals, resulting in degradation or loss of guidance. Some of the threats are not well understood, and will remain so for several years.
Several methods of enhancing GLS for providing acceptable signals for Cat. 3B and 3C (autoland) approaches have been proposed. One method is to enhance the satellite constellation by making use of another country's satellite system, such as the Russian GLONASS system. This approach places an added burden on the airborne equipment and has complex political implications. Another method uses so-called “pseudolites,” ground-based transmitters, located on or near the airport, which mimic satellites by providing additional range information to the airplane. Similar to ILS, this approach is impractical, because it entails large equipment expenditures and maintenance costs in addition to those of the differential GPS ground station. Also, neither of these approaches adequately addresses the environmental and other threats described above, which may produce unreliable GLS data for an indefinite period of time.
Accordingly, a need exists for a low-cost, low-maintenance, worldwide useful, airplane precision approach guidance system that is highly accurate and reliable. The present invention combines the best features of GLS and IRS to fulfill this need.
SUMMARY OF THE INVENTION
In accordance with this invention, an airplane precision approach guidance system and method are provided. The airplane precision approach guidance system includes: (i) GPS Landing System (GLS) components for receiving and processing signals from GPS satellites and a differential GPS ground station and generating a first set of velocities; (ii) an inertial reference system for generating a second set of velocities; and (iii) guidance software for determining a cross-runway velocity and a lateral distance from runway centerline based on received runway centerline coordinates and the generated first and second set of velocities. The airplane precision approach guidance system also includes flight instruments and an autopilot system for receiving and processing the information generated by the guidance software and for guiding the airplane through approach, touchdown, and rollout. The runway centerline coordinates may be stored at the ground station or in local memory. The ground station can also provide differential GPS information and satellite health status information.
In accordance with other aspects of this invention, the guidance software can be included in (or spread between) the global positioning system, the inertial reference system or the autopilot system. That is, for example, the guidance software may be executed by the autopilot processor, i.e., the guidance software may take the form of a subroutine or program included in the autopilot and carried out by the autopilot processor. Alternatively, the guidance software may be executed by a separate, stand-alone processor.
In accordance with still other aspects of this invention, the guidance software includes a first filter for generating a first velocity in a first predefined direction based on velocities in the first predefined direction from the first and second set of velocities, a second filter for generating a second velocity in a second predefined direction based on velocities in the second predefined direction from the first and second set of velocities, and a third filter for generating a cross-runway velocity and a lateral distance from runway centerline based on received runway centerline information and the generated first and second velocities. The third filter further generates the lateral distance from runway centerline based on a lateral distance from runway centerline received from the global positioning system.
In accordance with further aspects of this invention, the first and second filters estimate and store the velocity and acceleration biases in the first and second predefined directions of the velocities received from the inertial reference sy
Anderson Leonard R.
McIntyre Melville D.
Christensen O'Connor Johnson & Kindness PLLC
Mull Fred H.
Tarcza Thomas H.
The Boeing Company
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