During several sex scenes, actors seem to get switched without any explanation.
Chuck and Barney were supposed to install a telephone in a private jet. The plane shown was a small general aviation turboprop.
Stow-away passengers on a small airplane are not only easy to catch but also they can dangerously lower the quality of aircraft performance. It is impossible for the crew of a small airplane to miss any extra passengers especially in baggage area until after crossing Atlantic Ocean.
Small general aviation airplanes cannot cross Atlantic Ocean without making several stops for refueling along the way unless they are especially equipped with extra fuel tanks and are carrying minimal cargo including crew. In the movie, the aircraft seemed to be fully loaded along with two passengers hiding in baggage area, yet it managed to cross Atlantic Ocean faster than a jet.
If you leave the US in the afternoon, even a jet cannot reach Germany before late evening. In the movie, Chuck and Barney left after lunch break and arrived in Germany sometime around noon to have rest of the day left for their shenanigans.