The Pilot Handoff panel is used to switch the communication frequencies of your aircraft.  It displays all available frequencies while highlighting the frequency of the selected aircraft.  This frequency correlates directly with which air traffic controller has responsibility for the aircraft, and the ATC number displayed in the AC-State Information panel.  You can also use the Pilot Handoff panel for stealing aircraft under the control of other MACS stations.  To switch frequencies, simply click on the button displaying the desired frequency.  This action will cause the aircraft to transfer to the MACS station that is hosting that particular sector.

You can also steal an aircraft that is being controlled by another MACS station.  To do this, select the desired aircraft from either the All or View aircraft list.  The Pilot Handoff panel for this aircraft will highlight the current communication frequency and will have a "STEAL" button. 

Clicking the STEAL button will bring up a dialogue box confirming you want to steal the aircraft.  Click the OK button to continue or the CANCEL button to stop.  You can also stop by selecting "CANCEL" from the drop-down menu.  Once you click the OK button, the desired aircraft will now show up in your MACS station's Ctrl list. 

Notice that the aircraft's Pilot Handoff panel still highlights the frequency that was used by the aircraft before you stole it.  Now the aircraft is in a "transition" state, since it's on a Ctrl aircraft list that is on a MACS station that isn't associated with the aircraft's frequency.  At this point, you can control the aircraft any way you want, but you don't want to keep the aircraft in this transition state for long.  If you just want to quickly fix something with that aircraft, then issue the command and then click RETURN.  Clicking the "RETURN" button will send the aircraft back where it came from.  If you want to keep the aircraft permanently, then you need to click the frequency button for your own station, effectively handing off the aircraft to yourself.  By doing this, you will have full control over the aircraft.

Here you can see that after the stolen aircraft is transferred to your own MACS station, the last button in the Pilot Handoff panel will display "CONTROL" signaling you have full control over the aircraft.