ABSTRACT
A regular flight operation usually includes takeoff, climb, cruise, turn, descend, and landing. A civil aircraft is in cruising flight for much of the duration of its flight. Cruising flight is a major part of an air mission and is defined as a straight-line flight where the velocity and altitude are often kept almost constant. The specific speeds in straight-line level flight include maximum speed, cruising speed, minimum drag speed, maximum range speed, speed for absolute ceiling, and maximum endurance speed. The straight-line sustained level flight is possible at any permissible velocity. Ceiling is defined as the highest altitude at which an aircraft can safely have a straight-line level flight. Another definition is the highest altitude that an aircraft can reach by its own engine and have sustained flight. The cost of flight for a transport aircraft can be minimized by optimizing the cruising flight.
