To determine if you have to change planes, you must look at your flight itinerary for two specific indicators: the number of stops and the flight numbers. If you see a "Connection" or "Layover" listed with a significant time gap (e.g., 2 hours in Frankfurt), you will definitely be changing planes. In this case, you will have two different flight numbers (e.g., LH401 and LH102). However, you must be careful with "Direct" flights versus "Non-stop" flights. A non-stop flight goes from A to B with no pauses. A "direct" flight has a stop in city C but keeps the same flight number; in some cases, you stay on the plane, but in others, you are required to deplane and re-board the same or a different aircraft. The most certain way to tell is to check the change of gauge note in the fine print of your ticket. If the aircraft type changes (e.g., from a Boeing 787 to an Airbus A320), a plane change is guaranteed. Additionally, if your itinerary mentions a change of "Terminal," you are almost certainly moving to a different aircraft.