Here is my video playthrough of the final part of the game, with all the achievements, including this one.
1. This is after you hit the waterfall, and navigate the underwater section (which can also be another achievement).
2. Once you clear the underwater tunnels, and hit an open room...
3. Get your boat above a metal structure with a blue handle on it.
4. Use the crane on the back of your boat, attach to the handle, and pull it to open the mechanism.
5. Lower your boat into the mechanism.
6. Once locked in, put it in reverse, and get the fire as hot as you can.
The boat will back out, the balloon will lift off, and lift you into the air.