Complex sentence: For example, flights that require stopover merely for refuelling usually do not permit passengers disembarking from the aircraft while flights where there is a change of passengers may require that passengers disembark and stay at a holding area for security reasons and a proper headcount.
Split into simpler sentences: For example, flights that require stopover merely for refuelling usually do not permit passengers disembarking from the aircraft. On the other hand, flights where there is a change of passengers may require that passengers disembark and stay at a holding area for security reasons and a proper headcount.