Aircraft data radio with alternative channel selection

1. A data link radio system onboard an aircraft for communicating with a plurality of ground stations in the Aircraft Communications Addressing and Reporting System, wherein each ground station employs one of a Mode A protocol for analog communication and a Mode 2 protocol for digital communication, the data link radio system comprising:

a transceiver for communicating data bidirectionally with the plurality of ground stations, a particular one with which communication is occurring at a given time being referred to as a primary ground station;

a secondary receiver for receiving signals from the plurality of ground stations; and

a processor controlling operation of the transceiver and the secondary receiver;

wherein when the primary ground station employs one of the Mode A protocol and the Mode 2 protocol, the secondary receiver determines availability of an alternative ground station that employs another one of the Mode A protocol and the Mode 2 protocol, and wherein when the primary ground station becomes unavailable, the transceiver automatically is configured for and begins communicating with the alternative ground station.

2. The data link radio system as recited in claim 1 further comprising a database containing information related to each of the ground stations that employs the Mode A protocol.

3. The data link radio system as recited in claim 2 wherein the information for each station in the database designates a radio frequency.

4. The data link radio system as recited in claim 2 wherein the information in the database further includes a geographical location of each ground station.

5. The data link radio system as recited in claim 4 wherein data link radio system receives information regarding a geographical location of the aircraft, and the secondary receiver selects one of the plurality of ground stations as the alternative ground station based on geographical proximity to the location of the aircraft.

6. A data link radio system onboard an aircraft for communicating with a plurality of ground stations in the Aircraft Communications Addressing and Reporting System, wherein each ground station employs one of a Mode A protocol for analog communication and a Mode 2 protocol for digital communication, the data link radio system comprising:

a transceiver for communicating data bidirectionally with the plurality of ground stations, a particular one with which communication is occurring at a given point in time being referred to as a primary ground station; and

a secondary receiver for receiving signals from the plurality of ground stations;

wherein the secondary receiver selects one of the plurality of ground stations as an alternative ground station that is available for use by the transceiver, and wherein the primary ground station employs a first one of the Mode A protocol and the Mode 2 protocol and the alternative ground station employs a different second one of the Mode A protocol and the Mode 2 protocol, and

wherein if the primary ground station becomes unavailable, the transceiver automatically is configured for the second one of the Mode A protocol and the Mode 2 protocol and switches communication to the alternative ground station.

7. The data link radio system as recited in claim 6 further comprising a database containing information related to each ground station that employs the Mode A protocol.

8. The data link radio system as recited in claim 7 wherein the information in the database for at least some of the plurality of ground stations includes a radio frequency.

9. The data link radio system as recited in claim 7 wherein the information in the database further includes a geographical location of each ground station.

10. The data link radio system as recited in claim 9 wherein data link radio system receives information regarding a geographical location of the aircraft, and the secondary receiver selects one of the plurality of ground stations as the alternative ground station based on geographical proximity to the location of the aircraft.

11. A method for operating data link radio system onboard an aircraft that has a transceiver and a secondary receiver for the Aircraft Communications Addressing and Reporting System which comprises a plurality of ground stations, wherein each ground station employs either a Mode A protocol for analog communication or a Mode 2 protocol for digital communication, that method comprising:

the secondary receiver, scanning for one of the plurality of ground stations that is available and which is not in communication with the transceiver, thereby finding a alternative ground station;

storing information regarding communication with the alternative ground station; and

wherein when a ground station with which the transceiver has been communicating becomes unavailable, automatically configuring the transceiver for one of the Mode A protocol and the Mode 2 protocol employed by the alternative ground station and beginning communication with the alternative ground station.

12. The method as recited in claim 11 wherein the secondary receiver scans for an alternative ground station that employs a different one of the Mode 2 protocol and Mode A protocol than is being used by the transceiver.

13. The method as recited in claim 11 further comprising determining a location of the aircraft; and wherein the scanning selects one of the plurality of ground stations based on proximity to the location of the aircraft.

14. The method as recited in claim 11 further comprising providing a database containing a designation of a radio frequency for each of the ground stations that employs the Mode A protocol.

15. The method as recited in claim 11 further comprising providing a database containing a designation of a geographical location of each of the ground stations that employs the Mode A protocol.