Airlines, airports, and security authorities in a particular country enforce different policies on whether passengers may stay on the aircraft on routes which do not involve a change of aircraft. For example, flights that require stopover merely for refuelling usually do not permit passengers to disembark from the aircraft. On the other hand, flights where there is a change of aircraft (change of gauge) may require that passengers disembark and stay at a holding area for security reasons and a proper headcount.