Airspeed Indicator (ASI) Parts Lookup

One of the most critical parts of an aircraft’s instruments is the airspeed indicator. Each aircraft has specific airspeed requirements for things like takeoff, landing, and stalling that the pilot must be aware of during flight. A functioning airspeed indicator that accurately reports how fast the aircraft is therefore critical to safe operation.

An airspeed indicator can receive its information in several different ways. The most modern examples rely on computerized systems or GPS units to receive airspeed updates. For most of aviation history however, aircraft have used analog instruments that compare dynamic pressure (or ram air pressure) to static pressure.

This instrument, called the pitot-static system, is a differential pressure system that measures the dynamic air pressure from the pitot tube to the static pressure coming from a static port. Inside the instrument is a sealed diaphragm that receives both dynamic and static pressure from the pitot tube. Static pressure is also measured from inside the casing, but outside the diaphragm. The forces of static pressure both outside and inside the diaphragm cancel each other out, leaving only a measurement of total dynamic pressure, or ram pressure. As the aircraft accelerates, the dynamic pressure from the pitot tube increases, and causes the diaphragm to expand. This expansion is mechanically linked to the airspeed indicator, which displays the aircraft’s increasing speed on the indicator’s needle.

There are also different types of airspeed that must be considered. Indicated airspeed is the airspeed read directly from the indicator. It does not account for position, instrument error, or the effect that wind might have on the pitot tube. A trained pilot can account for these factors and determine the aircraft’s actual speed.

Airspeed indicators are typically marked with color-coded ranges to help the pilot fly safely and efficiently. These markings indicate certain critical ranges for operating different systems on the aircraft. The first is the white arc, which indicates the speeds at which an aircraft’s flaps can be safely used. The green arc is next, and represents the normal operating range of the aircraft, followed by the yellow arc, which pilots should only accelerate to in calm weather. Finally, is the red arc, or red line, that indicates the absolute maximum airspeed that the aircraft can sustain. High-speed aircraft, like military fighter jets, will also have Mach indicators to represent the aircraft’s speed relative to the speed of sound.

At NSN Parts Now, owned and operated by ASAP Semiconductor, we supply airspeed indicator parts and systems from top manufacturers around the world like Falcon, MGL Avionics, Mid-Continent, and Skysports.