You're welcome, I'm glad to help.
For Stowaway, I stay to the right of the crates until the 2nd lot of barrels come out of the back of the plane then I swerve into the plane.
If you are experiencing a timing problem & the plane takes off too quickly, you can try lowering your graphic settings to the minimum. Also quickly tapping on the 'up' or lean forward key will give some extra speed. You might try changing the setting for the frame limiter also. If you try this & you still can't do the mission you can always ask someone to do it for you.