Flight Instrument Parts Online Sourcing

Inside the cockpit there are many different mechanisms and dials that help inform the pilot about the status of aircraft. The mechanisms fall into two different categories: avionics and analog systems. This section will focus upon the analog systems that are housed on the dashboard.

First of all, it is important to understand how analog systems work. Pitot-Static flight instruments provide readings based upon the static air pressure and the dynamic pressure caused by the aircraft’s movement through the air. Airspeed indicators, altimeters, vertical speed indicators and are all powered this way.

The ASI is a differential pressure gauge that measures the difference between pitot and static pressure. The air speed indicator is directly influenced by the pitot tube. As wind blows across the nose of the plane, the total pressure (dynamic pressure and static pressure combined) is captured in the pitot tube. The pitot tube is connected to the air speed indicator via a small opening. The ASI is also connected to an alternate static source for the purpose of cancelling out the original static pressure. The result is a reading of the dynamic pressure appearing on the dial of the ASI. The ASI is calibrated in either knots or miles per hour.

There are different types of airspeeds that pilots need to be familiar with. Indicated airspeed is the direct reading obtained by the ASI. It does not reflect variables such as atmospheric density and installation. Calibrated airspeed is a reading that considers installation error and instrument error. True airspeed is corrected for altitude and nonstandard temperatures. Groundspeed is the actual speed of the aircraft on the ground.

Altimeters measure the height of an aircraft above a given pressure level. Inside an altimeter there is a stack of aneroid wafers that expand and collapse according to static pressure changes. A high static pressure results in the wafers collapsing. A low static pressure causes the wafers to expand. A metal linkage connects the wafers to the dial on the face of the altimeter. Compressed wafers equal a decrease in altitude and expanded wafers equal an increase in altitude. The pilot uses three pointers in their reading: 1,000 ft pointer, 10,000 ft. pointer, and the 100 ft. pointer.

Vertical speed indicators tell the pilot whether the aircraft is climbing, descending, or in level flight. The VSI is measured in terms of feet per minute. When the plane is level flight, the VSI reading should be zero.