A headwind is wind blowing in the direction opposite the direction the plane is traveling. An airplane flying into a headwind must exert more force to maintain a given speed. As a result, headwinds can noticeably increase the flight time of an aircraft. A flight from Los Angeles westward to Mumbai can take as much as 22 hours, while the same flight eastward can take only 17 hours. Due to the rotation of the earth and the way the sun illuminates it, air currents tend to blow stronger west to east.
A tailwind is the opposite of a headwind and occurs when a plane is flying in the same direction as the wind. A tailwind acts as a pushing force against the airplane, requiring it to exert less energy to travel a given speed. Flights traveling with prevailing winds can take much less time than the same flight returning against the wind.
Wind shear is a rapid shift in the direction or speed of wind over a short distance. Wind shear can be extremely dangerous to airplanes. Wind shear may initially speed up an aircraft, causing the pilot to respond by reducing power, then, rapidly, the wind shear will shift and slow the plane down. The plane, now operating at reduced power, is in danger of losing altitude and airspeed if the pilot does not respond quickly.
Crosswinds are wind currents that move perpendicular to the plane. Crosswinds are particularly important during takeoffs and landings when the airplane must maintain a straight course in relation to the runway. Planes that experience extremely high crosswinds also risk structural damage. Every airplane has a maximum crosswind limit beyond which it should not be exposed. While there is no FAA regulation defining a safe crosswind, airports may close if crosswinds become extreme, such as during hurricanes.
