The Truth needs you to fly the jetpack, land on a train and steal whatever they least want you to get. First you'll need to know how to fly the jetpack, which isn't hard if you just did the previous mission. Make your way to the green blip on the radar which you'll find is the train. Presuming you have sub machine gun ammunition, fly over the train, and hold R1 to auto target the guards. Kill the ten or so guards all the way along the train, then land at the back and work your way forwards. Shoot the blue crates until they blow up and see if anything is inside. The first two will have nothing, the last one will have the 'green goo'. Grab it, then fly back to The Truth as the airfield. Stand in the red circle and The Truth will take the goo and leave.
Mission Passed! $20,000
The Abandoned Airfield will now generate revenue up to $10,000 a day. Drop by each day and pick up the cash. All of the airfield's missions are completed.
The Jetpack is now available from the East side of the save house!
Now that you have the jetpack, it would be a good idea to use it to help you find the horseshoes in Las Venturas. You can read more about these in a separate guide, but if you intend to get 100% completion you need all of the side objectives, and they can be pretty hard to do when you've just found random ones, so I'd suggest following a guide through all of them. The next lot of missions you have to do are Woozie's at his casino. He can be found at the Yellow Dragon on the radar.