Air flight, or aerial transportation, is the transport of people and goods by means of aircraft. It is one of the most important forms of human transportation in the world, with more than a billion flights every day.

Airplanes are the largest and most advanced vehicles for carrying people in the air. They are designed to be safe, comfortable, and reliable for the passengers they carry.

The main parts of an airplane are its wings and tail surfaces, which sustain the aircraft in flight; movable surfaces that control the attitude of the plane in flight; and a power plant that provides thrust to push the vehicle through the air. Other components include an enclosed body (fuselage) to house the passengers, cargo, and crew; and a cockpit from which the pilot operates the controls and instruments to fly the airplane.

Wings of an airplane are shaped to make air move faster over the top of the wing. When air moves faster it has less pressure on the top of the wing than on the bottom, so the difference in pressure causes the wing to rise up into the air.

When a wing is lifted up into the air the weight of the aircraft is also lifted up. Because lift is heavier than weight, the wing takes longer to sink back down when it loses height.

An aircraft’s ability to lift itself up into the air depends on its fuel fraction, which is the percentage of the takeoff weight that is fuel. All animals and devices capable of sustained flight require relatively high power-to-weight ratios to generate enough lift and thrust to take off.

In a powered aircraft, thrust derives from the propulsive force of a rotating propeller; jet engines provide residual thrust by compressing air and then expanding it through combustion of introduced fuel.

The amount of energy needed to generate lift and thrust is called useful energy, which is the energy needed to overcome the drag associated with lift. Different animals and devices capable of flight vary in their efficiency of muscles, motors, and how well this translates into forward thrust.

Lift-to-drag ratios for practical aircraft range from about 4:1 for vehicles and birds with short wings to 60:1 or more for vehicles with long wings, such as gliders. Increasing the angle of attack of the aircraft relative to its forward movement also increases deflection of the wing, increasing lift but also generating additional drag.

Thrust, the force that propels an aircraft forward, derives from the propeller blades of a turbine or the rotating blades of a jet engine. All airplanes use engines to produce thrust, but some aircraft have more than one engine to increase the total available thrust for flight.

Aeronautical engineers study how to design airplanes that have low drag and a high power-to-weight ratio. They also look at ways to improve the aerodynamic properties of existing airplanes, such as by using lighter materials.

As with any form of transportation, aviation has its share of accidents. The most notorious was the crash of Trans World Airlines’ Super Constellation and United Air Lines’ DC-7 over the Grand Canyon in 1956, which killed all 128 passengers on board.