soo, first you have to steal a Hunter from the area 69, but it's heavily guarded. Once you've reached the Hunter, make sure you took down the SAM-sites. Go into the Hunter and fly to Los Santos on top of the "Library Tower". On top there are several FBI agents with snipers, rocket launchers and M16 assault rifles, take them down with the Hunter and land in top of the building. When you've landed you have to kill the primary target: the policecommander... You can do it with the Hunter, but the policecommander has Stinger, so it would be stupid. Kill him and his guards, grabble a parachute, sail down the building and get iinto the car parked at the street. You can keep this car, it's bullet-, explosion- and damageproof ;)