This end sequence is timed so I recommend reviewing this first instead of reading along.
Once in the plane, use your hand on the ladder once. Ben will walk in front of the truck and get shot at. Use your hand on the ladder again. Ben will climb up into the cockpit. Click on the middle panel. Select "Take Off". Then select "Post Take-Off". Then select "Gear". Lastly, select "Raise Gear". After a short cutscene, you will regain control of Ben on the truck.
Please note there is the opportunity to gain an optional achievement "LOOMing Seagull" before completing this achievement. If you are going for it, enter the truck cab. Click on the button just under the middle display.
Choose "Main Menu". Then select "Defense Systems". Then select "Machine Guns". Then select "Fire". The LOOMing Seagull achievement will pop. After Rip makes his comment start the real end sequence below.
Enter the truck cab. Click on the button just under the middle display. Choose "Main Menu". Then select "Defense Systems". Then select "Machine Guns". Then select "Control". Finally choose "System Off". A cut scene will show Ripburger's demise at which point you will earn the achievement. After the scene ends, walk Ben a little to the left and use your motorcycle to escape to trigger the end.