Get on cheat mode (A+B+START) and go to the last islands airport and type in the level select cheat (Left, right, up, down, L, R, hold start and press a) and go to the 1 mission and you will still be at ath airport. find a helecopter and press l and r at the same time and you will be in it. (watch out for buildings!)
I found this here -http://www.cheatmasters.com/cheats/14253/G...nce_cheats.html
It's probably bullsh*t but I want to be sure, getting a Heli in GTAA would be fun.