Aircraft Heading Indicator


For the safety and efficiency of flight, pilots have a number of aircraft instruments and avionics in the cockpit to aid in their awareness. The heading indicator, also known as a directional gyro, is an aircraft instrument that allows the pilot to know the aircraft’s heading. Heading indicators indicate both the primary heading and indirect bank of an aircraft, and they provide more accurate readings as compared to a standard magnetic compass. In this blog, we will discuss the aircraft heading indicator more in detail, explaining how they work and provide functionality.

The heading indicator operates utilizing a gyroscope which is tied to the yawing plane of the aircraft by an erection mechanism. Due to this configuration, an indication error is given by the aircraft instrument any time the aircraft yawing plane does not match the local Earth horizontal. To display such indications, the gyro axis drives the instrument display, either utilizing electronic means or a suction pump that is driven by the aircraft engine. The display of the heading indicator is a circular compass card, conveying measurements in terms of degrees.

Due to the rotation of the Earth, also known as apparent drift, the heading indicator will be faced with real drift. This can cause the instrument to become less accurate, warranting the need for a magnetic compass to reset the heading indicator periodically. To predict apparent drift, ω sin Latitude is used, also meaning that apparent drift is the highest when at the Earth’s poles. With a set latitude nut, the effect of Earth rate drift can be mitigated through the induction of real wander within the gyroscope. If this is not possible, the aircraft indicator needs to be manually set periodically during each routine in-flight check.

With higher quality aircraft heading indicators, such instruments may be slaved to a magnetic sensor referred to as a “flux gate”. Flux gates are useful as they can detect the magnetic field of Earth, allowing for the servo to correct the heading indicator automatically. With such benefits, the heading indicator does not require constant manual readjustment during routine in-flight checks and reduces the amount of workload required on the pilot’s behalf.

A remote indicating compass (RMI) is an instrument that was designed to compensate for the limitations and errors that are prevalent in early heading indicators. These apparatuses feature a pictorial navigation indicator and slaving control and compensator unit, and they are two panel-mounted. With the slaving control and compensator unit, a pilot may choose to either operate the device in a “slaved” or “free” mode. During a slaved gyro mode, the slaving meter will indicate the difference between the magnetic heading and the displayed heading. The free gyro mode, on the other hand, allows for adjustment of the compass card through a heading-drive button.

Whether you are operating in a small personal aircraft or a jumbo airliner, heading indicators and other avionics are critical to the safety of flight. When it comes time to begin sourcing the heading indicator parts and aircraft instrument components that you need for your operations, Just NSN Parts has you covered with everything you are searching for. Just NSN Parts is owned and operated by ASAP Semiconductor, and we can help you find the aviation, NSN, and electronic parts that you are searching for, new or obsolete. As a premier supplier of parts for the aerospace, civil aviation, and defense industries, we're always available and ready to help you find all the parts and equipment you need, 24/7x365. ASAP Semiconductor is an AS9120B, ISO 9001:2015, and FAA AC 0056B Accredited enterprise. For a quick and competitive quote, email us at sales@justnsnparts.com or call us at +1-714-705-4780.


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