A magnetometer is a sensitive instrument that measures the Earth's magnetic field strength and direction, enabling it to determine the aircraft's heading relative to magnetic north. Installed as a stinger or towed on a cable, airborne magnetometers feed data to compatible ADAHRS processors, where they serve as a heading reference within the attitude and heading reference system and provide supplementary data for heading calculation. Their outputs are used for redundancy, helping detect and isolate sensor failure.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is a magnetometer in an aircraft?
A magnetometer is a sensitive instrument used in aviation to measure the Earth's magnetic field strength and direction. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location.
In an aircraft, a magnetometer is a passive instrument that measures the magnetic field at the point where it is installed, sampling the background Earth magnetism at about one reading per second, or one hertz. Acting as a backup to alternative heading sensors, it detects changes in magnetic strength and orientation, supplementing the magnetic compass that pilots use for navigation. While a simple magnetic compass is a mechanical magnetometer that only measures direction, the airborne unit is usually a vector magnetometer that records both magnitude and direction, helping the flight-management system correct for deviation caused by flowing electrical currents, magnetized aircraft parts, or conflicts with the Earth's magnetic field.
What does a magnetometer do in aviation?
A magnetometer is a sensitive instrument that detects changes in magnetic fields and determines magnetic heading. In aviation, magnetometers provide heading information, enable pilots to navigate safely and efficiently, and serve as the heading reference within the Attitude and Heading Reference System (AHRS). Multi-axis magnetometers measure the strength and direction of the magnetic field along each aircraft axis, after which hard- and soft-iron calibration must be completed before the unit can be accepted as the heading source.
The magnetometer's output is distributed to several cockpit indicators: the heading indicator, the Horizontal Situation Indicator (HSI) that receives magnetic-north reference from a magnetic-slaving transmitter, and the G1000 suite, whose heading display is primarily a gyroscopic instrument slaved to the GMU44 magnetic compass for continuous magnetic alignment.
How does an aircraft magnetometer work?
An aircraft magnetometer works by sensing the direction and strength of the Earth's magnetic field. Most modern installations use a fluxgate magnetometer, which consists of a small magnetically susceptible core wrapped by two coils of wire. One coil, the drive winding coil, carries alternating current that repeatedly magnetises and demagnetises the core. The second coil, the sense winding coil, has a current induced in it whenever the core's symmetry is disturbed by an external magnetic field and this current becomes the magnetometer's output signal. Like a simple compass, the fluxgate device measures the direction of an ambient magnetic field, but it does so electrically and continuously. The heading is the horizontal component of that field. Alternative technologies like proton precession magnetometers measure the resonance frequency of protons in the magnetic field, while Hall-effect and magneto-resistive elements detect deflected electrons or varied resistance in the presence of a magnetic field. Whichever sensor is fitted, the system converts the detected vector into electrical data that the aircraft's avionics can display and use for directional reference.
An aircraft magnetometer works by sensing impalpable fluctuations in Earth's magnetic field. Electronics within the measuring device determine magnetic strength, while microelectronics track infinitesimal variations in real-time. To keep the readings clear, the detector is separated from the aircraft's own magnetic disturbance; on my aircraft it was held in a surface-to-air missile that jutted from the rear. As I flew the measurements appeared graphically on a display before me.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
What are the signs of magnetometer failure in aviation?
The signs of magnetometer failure in aviation are listed below.
- If a magnetometer fails in flight there will be a slight reduction of engine power.
- Variation in voltage readings or inconsistent spark intensity can be red flags for magnetometer failure.
- Abnormal noises or vibrations may result from magnetometer failure.
- Inconsistent spark intensity can be indicative of magnetometer failure.
- Irregular operation, backfiring, or reduced power output indicates magnetometer failure.
