Aero gas turbines have an exhaust system that passes the turbine discharge gases into the atmosphere at a velocity and direction appropriate to the flight condition. A second nozzle exists in (high bypass) for discharging the air that has bypassed the fan. Thus it provides the thrust force required for all flight conditions except landing where the thrust reverse system may provide the dragging force needed for the aircraft to stop within an appropriate distance. For turbo-propeller engines, the major part of thrust is developed by the propeller, and the exhaust gases make little contribution.