Introduction
Older airplanes are fitted with so-called ‘steam gauges’, the analogue instruments that have been installed in general aviation cockpits for decades. Newer airplanes may have a ‘glass cockpit’, with instruments and information displayed digitally on a screen.
Whichever instruments you fly with, the inputs to them and how they are affected by atmospheric conditions and aircraft manoeuvring has not changed.
The system parts
This system consists of a ‘pitot tube’ and a ‘static port’. They are often combined into the same tube, but may be separate.
Instruments that use measurements from this system are the airspeed indicator, the altimeter, and the vertical speed indicator.
The pitot tube
A pitot tube contains two holes that each measure pressure from the incoming airflow. The front-facing hole measures ‘stagnation pressure’, and the side- or rear-facing hole measures ‘static pressure’. The difference between these two measurements results in ‘dynamic pressure’, which can then be used to calculate airspeed. A pitot tube with both of these holes is also known as a pitot-static tube.
Care & maintenance
Pitot tubes are very important to safe flight and must remain clean and clear. A blocked pitot tube will result in incorrect airspeed readings and endanger the flight. The pilot’s ability to read the correct airspeed is essential.
When not in use, pitot tubes should be covered with a ‘Remove Before Flight’ tag. A tube left without a cover risks being blocked by dirt or insects.
Checking the pitot tube holes are clear is part of the pre-flight checklist.
