Ideal goal of the future air traffic system is recognized that every aircraft can freely fly in the sky to optimize its own performance. Since the trajectory optimization depends on aircraft performance characteristics, the performance model is one of the key elements for practical applications. As for cruise phase, it is known that a periodic dynamic maneuver is the optimum when a simple model is used, but the maneuver is not actually used in real flight operations. This paper studies what parts of the model characteristics are influential on the optimality of the periodic dynamic maneuver in cruise flight. It reveals that engine performance model and atmospheric characteristics are two influential parameters, which justify the optimality of steady horizontal flight for cruise phase.