[.041 Safety Wire]

A small refresher course for you guys. The airspeed of the aircraft is calculated through the difference between ram air pressure which is read by the pitot head and static pressure which is read by the static port. The pitot head is normally mounted outside of the propeller slipstream so it is in undisturbed air. The static port is usually on the side of the aircraft and operates in the boundry layer. The speed that the indicator in the cockpit shows is the IAS or indicated airspeed. The difference after taking into account the density of the outside air and several other factors is the true airspeed.