Redundant altimeter system with self-generating dynamic correction curve

• US 6,626,024 B1
• Filed: 03/02/2001
• Issued: 09/30/2003
• Est. Priority Date: 03/02/2001
• Status: Expired due to Term

• Current Assignee: Innovative Solutions and Support Incorporated
• Original Assignee: Innovative Solutions and Support Incorporated
• Inventors: Hedrick, Geoffrey S. M.
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): Jenkins, Jermaine
• Application Number:
  US09/798,229
• Time in Patent Office: 942 Days
• Field of Search: 731/79, 738/652, 731/78.R, 73/17.8, 731/81, 731/82, 733/84--87, 701/4, 342/120
• US Class Current: 73/1.78
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01C 5/005 altimeters for aircraft G01C5/02, G01C5/06 take precedence

Abstract

In an aircraft conventionally-including a redundant pair of independent primary altitude determination systems of accuracy certified for RVSM operations, an initially loosely calibrated backup altimeter receives independent static pressure data for use in calculating altitude. During normal flight of the aircraft, the current altitude determinations of the primary altimeters and, using a recursive filter, the static source error correction (SSEC) of the backup altimeter is recursively adjusted until the SSEC attains a steady-state value with which the calculated altitude determinations by the backup altimeter accurately conform to the altitude determinations of the primary altimeters. Through this self-correction functionality the backup altimeter is rendered sufficiently accurate for permitted use in RVSM airspace in the event of a failure of one of the primary altitude determination systems.

Claims

1. An aircraft altitude measuring system, comprising:

means for determining an actual error-corrected altitude of the aircraft during flight to a first predetermined level of accuracy;

means for calculating an estimated altitude of the aircraft during flight as a function of at least one variable;

means for obtaining data representing said at least one variable during flight of the aircraft and for delivering said data to said calculating means;

means for recursively comparing said calculated estimated altitude with said determined actual altitude of the aircraft and for dynamically generating from said comparison a static source error correction of said function during flight so that said function achieves in calculating the estimated altitude at least a second predetermined level of accuracy; and

means for storing said static source error correction for use in subsequent calculation of estimated altitude.

2. The system of claim 1, wherein said means for determining an actual altitude of said aircraft during flight comprises two independent error-corrected altimeters.

3. The system of claim 1, wherein said means for comparing operatively compares said determined actual altitude and said calculated estimated altitude substantially continuously during the flight of the aircraft.

4. The system of claim 1, wherein said at least one variable is static air pressure on an exterior skin of the aircraft during flight.

5. The system of claim 1, wherein said means for comparing and generating comprises a Kalman filter.

6. A method of providing redundant altitude measurements for an aircraft during flight, comprising the steps of:

determining an actual error-corrected altitude of the aircraft during flight to a first predetermined level of accuracy;

calculating an estimated altitude of the aircraft during flight as a function of at least one variable;

obtaining data representing said at least one variable during flight of the aircraft;

recursively comparing said calculated estimated altitude with said determined actual altitude of the aircraft, and dynamically generating from said comparison a static source error correction of said function during flight so that said function achieves in calculating the estimated altitude at least a second predetermined level of accuracy; and

storing said generated static source error correction for use in subsequent calculations of estimated altitude.

7. The method of claim 6, wherein said determining of the actual altitude of the aircraft during flight is performed using two independent error-corrected altimeters.

8. The method of claim 6, wherein said step of comparing is performed substantially continuously during flight of the aircraft.

9. The method of claim 6, wherein said at least one variable is static air pressure on an exterior skin of the aircraft during flight.

10. The method of claim 6, wherein said step of comparing and generating is performed using a Kalman filter.

11. In an aircraft having a first primary altitude indicator system operable for determining current altitude of the aircraft to a precision sufficient for Reduced Vertical Separation Minimum (RVSM) flight operations of the aircraft and a second primary altitude indicator system operable for determining, independent of said first primary system, the current altitude of the aircraft to a precision sufficient for RVSM flight operations, each of said first and second primary systems being connected to primary static pressure ports defined on a skin of the aircraft, the improvement comprising a self-calibrating backup altimeter system comprising:

a controller for receiving static pressure data from an auxiliary static pressure port independent of said primary ports and having a stored Static Source Error Correction (SSEC) for use in calculating, using the received static pressure data from the auxiliary port, an estimated current altitude of the aircraft, and

said controller being connected for receiving from the first and second primary systems the current altitude determined by said first and second primary systems and being operable for comparing the estimated current altitude with the received current altitude determined by said first and second primary systems, for correcting the SSEC in accordance with said comparison so that the estimated current altitude accords with the received current altitude determined by said first and second primary systems, and for storing the corrected SSEC for use in calculating a new estimated current altitude for comparison with newly-received current altitude determinations from said first and second primary systems.

12. In an aircraft in accordance with claim 11, said controller being operable for correcting the SSEC in accordance with said comparison, so that the estimated current altitude accords with the received current altitude determined by said first and second primary systems, by using a recursive algorithm that progressively minimizes differences between the estimated current altitude and the current altitude determined by said first and second primary systems.

13. In an aircraft in accordance with claim 12, said recursive algorithm comprising a Kalman filter.

14. In an aircraft in accordance with claim 11, said controller being connected to at least one of said first and second primary systems for receiving from said at least one primary system a calculated flight speed of the aircraft for use in correcting the SSEC.

15. In an aircraft in accordance with claim 11, said backup altimeter system further comprising an indicator actuatable by said controller when the corrected SSEC has attained through said correcting of the SSEC a steady-state value that provides sufficient accuracy in the estimated current altitude for use of the backup altimeter system for RVSM flight operations.

16. In an aircraft in accordance with claim 13, said backup altimeter system further comprising an indicator actuatable by said controller when the corrected SSEC has attained through said correcting of the SSEC a steady-state value that provides sufficient accuracy in the estimated current altitude for use of the backup altimeter system for RVSM flight operations.