Magnets with a magnetic field strength of 0.159 A/m or greater, and those that are measurably effective at a distance of 2.1 m or more, are classified as dangerous goods by the FAA and IATA for their potential to interfere with instruments on board a plane. Given their status, magnetic materials are required to be handled by those who have received and maintained training in the handling of dangerous goods.
Magnetrons
Magnetrons are devices which utilize electrical and magnetic currents to create heat output. When packed for air shipment, magnetrons must be packed so that the polarity of individual units oppose one another. This method of packing will temporarily cancel out the magnetic fields of the devices, preventing the device from interfering with the plane's instruments.
Permanent Magnets
Permanent magnets are made from materials that retain their magnetic fields unless demagnetized by environmental changes or manual intervention. When packing permanent magnets for shipment by air, keeper bars must be installed. These bars are placed around the poles of a permanent magnet to complete the magnetic circuit, preventing external metal from being affected.
Magnetic Field Strength
Permanent magnets packed to ship by air can not have a magnetic field that exceeds 0.418 A/m. A magnetic field of this strength, regardless of the use of keeper bars or other precautions, is considered unsafe for storage aboard airplanes, as it will cause significant disturbances in instrument operations. Most notable among the malfunction potential in a strong magnet is the potential for magnetic compass deflection, which endangers the aircraft, its passengers and cargo.
Compass Deflection
Permanent magnets can not produce a magnetic compass deflection of more than 2 degrees. Greater interference can produce dangerous malfunctions in a plane's compass, driving it far off course or inhibiting its ability to take off or land from optimal directions. These variances in the plane's operations have the high potential to cause a crash, endangering the lives of passengers and other nearby people.
Tags: magnetic field, magnetic fields, compass deflection, dangerous goods, keeper bars, magnetic compass, magnetic compass deflection