Bad Piggies When Pigs Fly Level 3-15 is three starred in two steps. Not using the propeller is a rocky, explosive trip down to the bottom of the chasm, while reaching the box requires very systematic use of the propeller and soda bottles during a smooth trip across the entire level.
If you have a different strategy for completing this level feel free to leave a comment below.
I used two soda bottles to avoid using the propeller — use one to go right almost immediately followed by the other to go left. Time it right to avoid the TNT, then break the ballons to drop down the right path towards the finish line.