In three locations in the city, there are Sparrow helicopters that, when entered, will begin the "Chopper Checkpoint" missions. Completion of the mission, "Rub Out", is required to unlock them. After completion of the mission "G-Spotlight" for InterGlobal Films, a fourth and final mission will be available.
The premise is simple - navigate the checkpoint course set out for you. Unless you plan to retry these missions to beat your best time, you can take this as fast or as slow as you want. Some checkpoints are positioned close to buildings, trees and other obstacles, so taking it easy is strongly advised if your chopper skills aren't up to scratch.
The locations are listed below:
Vice Point - On an open grassy area, in the center of the apartments across the street and east of the Links View Apartments and the Vice Point Pay 'n' Spray.
Ocean Beach - On the roof of an apartment southeast of the Ocean Beach Pay 'n' Spray, accessed by helicopter or a nearby Unique Stunt Jump.
Little Haiti - On the roof of a building on the southern side of the block east of Kaufman Cabs Taxi Depot.
Downtown - At the offices where you gained access to the rooftops in the mission "G-Spotlight". Completion of that mission is required for access to it.
Your reward for each checkpoint course is $100.