well you can use ingame trainer's quick boost option and it will send you up as high as you want, but believe me, you don't want to go that high. When I got really high up in the sky I saw black parts of Liberty city, the edges of the map turned black. I think that's the end of draw distance or sth like this.
someone please help me!!! I really want to fly the flyus jumbo jet I have superspawner and everything else needed to fly the jet. Except the flying car wont go up and down so please someone tell me the keys Thanks