Device and method for combined altitude display

1. An apparatus comprising:

a first altitude input interface, wherein the first altitude input interface receives a first altitude value;

a second altitude input interface, wherein the second altitude input interface receives a second altitude value, wherein the second altitude value indicated by the second altitude input interface has a cyclical range of one or multiple 0 to 360 degree angles;

a data fusion component coupled to the first altitude input interface and the second altitude input interface and configured to calculate a third altitude value based on the first altitude value and the second altitude value; and

an altitude output interface coupled to the data fusion component, wherein the altitude output interface outputs the third altitude value.

2. The apparatus of claim 1 ,

wherein the first altitude value comprises a first altitude value sign, one or more most significant digits of the first altitude value, and one or more least significant digits of the first altitude value,

wherein the third altitude value comprises a third altitude value sign, one or more most significant digits of the third altitude value, and one or more least significant digits of the third altitude value,

wherein the data fusion component calculates the least significant digits of the third altitude value based on the second altitude value, and

wherein the data fusion component calculates the third altitude value sign and most significant digits of the third altitude value based on the first altitude value sign, most significant digits of the first altitude value, and a roll-over or a roll-under of the second altitude value.

3. The apparatus of claim 2 , wherein the number of the most significant digits of the first altitude value is the same as the number of the most significant digits of the third altitude value.

4. The apparatus of claim 2 , wherein the number of the least significant digits of the first altitude value is the same as the number of the least significant digits of the third altitude value.

5. The apparatus of claim 2 , wherein the number of the most significant digits of the first altitude value is 1.

6. The apparatus of claim 2 , wherein the number of the most significant digits of the first altitude value is 2.

7. The apparatus of claim 2 , wherein the first altitude input interface receives the first altitude value from an air data module.

8. The apparatus of claim 7 , wherein the second altitude input interface receives the second altitude value from a central air data computer.

9. A method, comprising the steps of:

receiving, by a first input interface, a first altitude value;

receiving, by a second input interface, a second altitude value, wherein the second altitude value has a cyclical range;

calculating, by a data fusion component, at least one most significant digit of a third altitude value based on at least one digit of the first altitude value and on a roll-over or roll-under of the second altitude value; and

outputting the third altitude value.

10. The method of claim 9 , wherein calculating the third altitude value based on the first altitude value and the second altitude value comprises:

calculating a sign of the third altitude value based on the second altitude value, a sign of the first altitude value, and one or two digits of the first altitude value;

calculating one or more most significant digits of the third altitude value based on the second altitude value and one or two digits of the first altitude value; and

calculating one or more least significant digits of the third altitude value based on the second altitude value.

11. The method of claim 9 , wherein calculating the third altitude value based on the first altitude value and the second altitude value comprises:

calculating a sign of the third altitude value based on a sign of the first altitude value, one or more digits of the first altitude value, and a roll-over or a roll-under of the second altitude value;

calculating one or more most significant digits of the third altitude value based on one or more digits of the first altitude value and the roll-over or the roll-under of the second altitude value; and

calculating one or more least significant digits of the third altitude value based on the second altitude value.

12. The method of claim 9 , wherein receiving, by the first input interface, the first altitude value comprises receiving the first altitude value via an air data module.

13. The method of claim 12 , wherein receiving, by the second input interface, the second altitude value comprises receiving the second altitude value via a central air data computer.

14. The method of claim 9 , further comprising:

receiving, by the second input interface, one or more synchro signals; and

converting the one or more synchro signals into the second altitude value.

15. A computer system comprising:

a processor;

a memory coupled to the processor, wherein the memory stores a program that, when executed by the processor, causes the processor to:

receive a first altitude value;

receive a second altitude value, wherein the second altitude value has a cyclical range; and

calculate at least one most significant digit of a third altitude value based on at least one digit of the first altitude value and on a roll-over or a roll-under of the second altitude value.

16. The computer system of claim 15 , wherein the program, when executed by the processor, causes the processor to calculate the third altitude value by causing the processor to:

calculate a sign of the third altitude value based on the second altitude value, a sign of the first altitude value, and one or two digits of the first altitude value;

calculate one or more most significant digits of the third altitude value based on the second altitude value and one or two digits of the first altitude value; and

calculate one or more least significant digits of the third altitude value based on the second altitude value.

17. The computer system of claim 15 , wherein the program, when executed by the processor, causes the processor to calculate the third altitude value by causing the processor to:

calculate a sign of a third altitude value based on a sign of the first altitude value, one or more digits of the first altitude value, and a roll-over or a roll-under of the second altitude value;

calculate one or more most significant digits of the third altitude value based on one or more digits of the first altitude value and the roll-over or the roll-under of the second altitude value; and

calculate one or more least significant digits of the third altitude value based on the second altitude value.

18. The computer system of claim 15 , wherein the program, when executed by the processor, further causes the processor to:

calculate a barometric altitude adjustment based on local weather conditions; and

calculate the third altitude value based in part on the barometric altitude adjustment.

19. The computer system of claim 15 , wherein the program, when executed by the processor, further causes the processor to output the third altitude value and an altitude type identifier to a display, wherein the altitude type identifier indicates whether a displayed altitude is a baro adjusted altitude or a baro adjusted synchro altitude.

20. The computer system of claim 15 , wherein the program, when executed by the processor, further causes the processor to:

receive a fourth altitude value;

determine whether the first altitude value and the third altitude value differ by more than a predetermined value;

output the third altitude value when the first altitude value and the third altitude value differ by less than the predetermined value; and

output the first altitude value when the first altitude value and the third altitude value differ by more than the predetermined value.