What is the error of a magnetic compass caused by magnetic influence from the aircraft's structure called?

The error of a magnetic compass caused by magnetic influence from the aircraft's structure is referred to as deviation. This deviation occurs because the magnetic compass is influenced by the magnetic fields generated by the aircraft's metal structure and electronic equipment. These nearby magnetic sources can distort the reading of the compass, leading to inaccuracies that vary depending on the aircraft's heading.

Pilots must be aware of deviation and can correct for it through calibration and by using a deviation card, which details the compass errors at various headings. Understanding deviation is crucial for navigation accuracy in aviation, enabling pilots to make informed decisions while flying.

Variation, on the other hand, is the difference between magnetic north and true north and is a geographic phenomenon rather than one caused by the aircraft itself. Magnetic tension and agonic error do not specifically relate to compass errors due to the aircraft's influence.