The AL channel found on the Call channel tab of the programmer is used for programming the NOAA Weather Alert channel for your location.  This channel is used for the weather alert function of the radio to monitor the weather channel "in the background" as you operate on other channels. Should activity be heard on the weather channel, the radio would switch automatically to this channel. 

You can engage the Weather Alert function through the programmer at Settings | Radio Menu Settings | Scan / Weather.  Set this option to Weather Alert to turn the function on when you program from the computer.  The function can be turned on and off through Menu item 42 from the face of the radio. 

This option is only available in the TM-271 radio and not the TM-471 (considering the weather channel frequencies are all in the 2M band).