Cruise

The cruise portion of a flight usally consists of heading (direction of flight) changes only. Typically a constant airspseed and altitude will be maintained until the aircraft arrives near the destination and then enters the descent phase of flight.

Aircraft are usually designed for optimum performance at their cruising speed. The designer will try to maximize the Lift / Drag (L/D) ratio of the airframe for that speed. There will also be an optimum altitude for a particular aircraft type. This altitude is usually where engine efficiency will be maximum.