The easiest way to do this is unlock the Platnium RPG and the Lopez Mansion by completing the Hitman activities and the Carnales storyline respectively. Get a 4-star police notoriety, and run into the house. Go out on the balcony and RPG the helicopter. You will get only minor damage from the cops on the ground, and only very rarely will one enter your crib.
Use this work of art as a reference
1. locate and head to sloppy seconds on your map... (red square)
2. start killing cops til you reach 4 stars
3. hide behind the building on the lifted piece of ground (blue arrow)... you have to go between the 2 buildings across the street from sloppy seconds to get there.
4. you wont have to worry about cops if you stay near the fence because they will spawn on the other side of it... just worry about the choppers
A. shoot the pilot (if you can) not the chopper... it will crash if you kill the pilot
B. the sniper and the 44 shepherd work BEST on the pilot (1 shot if you hit him)
C. bring the rpg, shot gun, and uzi, there may be times when you can't hit the pilot
D. STAY NEAR THE FENCE... it keeps the cops on the other side, and it helps towards your chopper destruction count because if you are too far from the chopper crash it wont count