So I'm hunting for the UFO parts and there's one on a bridge support that can only be accessed via parachute. The only chute that I know of (Ammunation doesn't stock them yet in my game) is on the top of the big yellow crane in Downtown Los Santos. So I climb up to get it. I don't want to use it so I climb back down. I have maybe three or four more ladders to go before I get back under the roof to the base of the crane when Franklin misses a step and walks off the side of the platform rather than grabbing the next ladder. He almost immediately goes into parachute mode, but I don't open it. Even though the fall will be fatal I'm curious to know if he would keep it since it wasn't opened.
Instead I get the WHAT THE f*ck of a life time when he rockets up way past the sky scrapers and never comes down. Parachute is NOT opened and the character is fully controllable. Pressing forward on the stick makes him dive down, letting off causes him to regain altitude. So I just flew from Downtown Los Santos to where the Great Ocean Highway crosses Cassidy Creek to get the UFO part. No plane. Just Supermanning it. When I got there I opened my chute and fell like normal.
Unfortunately the UFO part there is a bit tricky to get, you must parachute to it but before you can touch it your parachute hits the bridge causing you to fall to your death. It's a very small window to fit into.