SOUTH SAN FRANCISCO, Calif. — AIRSPEED: WEIGHT, DRAG, THRUST, LIFT
Federal safety investigators say the Asiana Airlines Boeing 777 that crashed at San Francisco International Airport had slowed significantly below the target landing speed of 137 knots (158 mph) well before it reached the runway threshold. An attempt in the last seconds of flight to increase speed came too late. Here's why an airplane's air speed is so important:
— For an airplane to fly, its wings must generate lift to overcome the craft's own weight, which is the force of gravity, and drag, which is the air's resistance to the movement of the plane.
— The thrust of jet engines accomplishes this by pushing an aircraft forward and causing air to flow over and under the wings.
— Air speed is critical to keeping air flowing at rates specific to each type of aircraft in order to allow the wings to generate the lifting force.
— If the airplane's air speed is too slow, the wings will stop generating sufficient lift and the craft will fall. An aircraft does not have to stop moving forward for it to lose lift.
