 Additionally, during aircraft evacuations, it has been found that the majority of overwing window exit designs of Boeing 737 (NG) Next Generation Line along with the Airbus A320, hamper evacuation in comparison with traditional floor level exits due to the inherent "step up and through motion" required of passengers as they exit the aircraft, unlike the designs of older generation wide body aircraft such as the McDonnell Douglas DC-10 and Lockheed L1011 which are all floor level.There are principally two types of overwing exits (excluding the full-sized door on the likes of the Boeing 747, which is not considered an overwing exit - referred to as a Type I exit) in use on modern aircraft.These disposable hatch type exit are called Type IIIA and Type IIIB exits.