This mission is given to you by Devin Weston ("D" on map) and can be started by either Franklin or Trevor. Switch to Trevor and learn a bit about the facial recognition system that is on the helicopter you're controlling (as well as learn about Franklin's past deeds). Guide the helicopter to Hawick and start scanning the targets.
You won't find Chad in the first set of targets, but he will be among the second set. Once you get a positive ID on him, keep an eye on him and follow him until he leads you to the car. Once he gets to it, he'll enter the car and take off, so you will need to watch him as he speeds through traffic. Despite his speed, he isn't too hard to follow, since he has moments where he will stop for a second or two.
He'll eventually enter a parking garage and you won't be able to see him normally. However, you can trigger a mode that gives you infrared, meaning you'll see people's body heat through the walls. Use this to scan (zoom in when told to) the various heat signatures, until you've found Chad, which is when you'll switch to Franklin.
Keep your gun aimed at Chad and slowly move towards the vehicle. Quickly get inside and exit the garage, heading towards your objective. Not too long after you've exited the garage, you will get a 2-star wanted level, so you will need to lose the cops and not damage the care too much. After losing them, bring the car to the airport and then leave to finish the mission.