Not sure if Mission Manger can work with SARapp to add a responding feature.
Once a call goes out it would be nice if members could respond to the callout from the app and show and ETA. Once they are shown as available or enroute it would allow them access to subject information so they can look for the missing person as they are heading on scene. MM could have a spot for leadership to view how many units are responding and subtotaled by unit and maybe tie it into the check-in tab for staging.