What does "air K9" mean? Is it a flying dog with a helmet and XTS 5000 flying overhead. Just kidding. Seriously I am not sure what this unit is. Any clarification would be appreciated.
Since the Air units and the K9s work citywide, back in the 1970s they decided to establish a specific frequency for them to always monitor rather than twirling around the dial as they went over or through different divisions, and Communications wouldn't have to go hunting for them when they were needed. They also began multicasting all urgent/emergency "hotshot" calls there too.
They first used VHF Tac 2 (154.77) for it, but because of an interference issue they soon switched to Tac 1 (154.83). When the Astro Saber III radios came along in the late 90s, they dedicated the 506.7125 freq for it and named it the "Hotshots and
Air / K-9 Hailing Channel," which became simply "Air/K9." It was originally in the Ch 21 slot, but was moved to Ch 26 when they reconfigured the patrol radios in 2004.
Here's part of the 2004 channel lineup and a now-outdated screenshot of the RTO's channel-select screen, showing Air/K9 among the frequencies (in white) automatically preselected for an "Officer Needs Assistance" call in Central Division: