Following take-off, the aircraft has to climb to a certain altitude (typically 30,000 ft or 10 km) before it can cruise at this altitude in a safe and economic way. A climb is carried out by increasing the lift of wings supporting the aircraft until their lifting force exceeds the weight of the aircraft.

Immediately after the wheels leave the ground, a plane enters the initial climb phase, which is a highly choreographed sequence of mechanical and aerodynamic changes. First, the pilot or the auto-flight system initiates "Positive Rate" and retracts the landing gear to reduce drag. Next, as the aircraft gains speed and altitude, the flaps and slats are incrementally retracted to transition the wing from a high-lift "takeoff" configuration to a more efficient "cruise" shape. At around 1,000 to 1,500 feet, the pilots perform a "Thrust Reduction" to move the engines from takeoff power to climb power, which is quieter and more fuel-efficient. The aircraft then follows a specific Standard Instrument Departure (SID) route, which is a pre-defined "highway in the sky" that ensures separation from other planes and avoids noise-sensitive residential areas. Throughout this climb to "cruising altitude" (typically 30,000 to 40,000 feet), the pilots stay in constant communication with Air Traffic Control (ATC) while monitoring engine performance and weather radar to ensure a smooth ascent into the stratosphere.