Pitot Tube

Pitot Tube (pronounced "pee-toe") is an instrument mounted on the exterior of the aircraft that measures the total (ram) air pressure caused by the aircraft moving through the air. By comparing this with static pressure, the airspeed indicator calculates indicated airspeed (IAS).

Pitot tubes must be heated to prevent ice blockage, which can cause erroneous airspeed readings — a factor in several aviation accidents. Modern aircraft have multiple redundant pitot-static systems.