The Zeppelin NT, being designed more than 60 years after the last generation of Zeppelins were built as well as making use of advances in material science and computer-aided design, has been claimed to overcome some of the typical disadvantages of airships, such as maneuverability, safety, and economics. In particular, the propulsion system offers significantly increased safety. In standard operations with a maximum payload, the gas cells do not create enough buoyancy to make the whole ship "lighter-than-air." The negative buoyancy is overcome with the application of engine power. The buoyancy can change when traveling with a reduced payload and partially emptied fuel tanks, but typically the Zeppelin NT starts a journey with a net downward force of about ; on long trips, the airship can become lighter–than–air if much of its fuel is consumed.