It is obvious how important the pitot tube is for aircraft. Birgen Air accident is one of the important examples of this. Before explaining why there are pitot tubes on the tail area in B737 types of aircraft, we need to give some information about pitot tubes;
Pitot tubes are part of the pito-static system that located in areas where the airflow of the aircraft is smooth (eg; nose, wings). The diaphragm in the pitot tube moves with the dynamic pressure it is due to the speed of the air and this movement is reflected in the scale on the speedometer. The measured value confirms each other’s values before sending the indication in the cockpit. Pitot tubes also have an electrical anti-icing system against temperatures up to -55 degrees at high altitudes.
In 737 type aircrafts, there are two pitot tubes on the dorsal fin area. These tubes send information to the elevator feel and centering unit. This is to provide artifical feeling for control column.
Moving the elevator at high angles causes sudden descending/ascending or damage to structural elements. Therefore, at these speeds, the moving range must be limited.
This limitation is provided by the elevator feel and centering unit. If the aircraft flies faster, the more force is required to move the elevator up and down and less control input is required at higher speeds. This force (artificial feeling) helps to prevent the pilot from over-controlling the aircraft at high speeds.