Definition
Magnetism in a part where the magnetic field runs along the long axis of the part, used in magnetic particle inspection to reveal cracks and flaws oriented across the part (perpendicular to its length).
Plain English
The part is magnetized end-to-end along its length, which makes any cracks running across it show up clearly.
Context Anchor
Seen in aircraft maintenance and engine inspection discussions, especially when checking steel parts for hidden cracks without damaging the part.
Derivation
From Latin longitudo, meaning length. Longitudinal simply means 'along the length,' which describes the direction the magnetic field flows through the part during this type of inspection.
Why Pilots Care
Uncorrected longitudinal magnetism creates heading errors that can lead to navigation deviations, especially on east-west courses.
Analogy
Think of a simple bar magnet: one end is a north pole and the other is a south pole. Longitudinal magnetism treats the inspected part in a similar end-to-end way.
Intuition Check
Do not read “longitudinal” here as just “front-to-back on an airplane.” It means the magnetic field runs along the length of the inspected part.
Example Sentence 1
The technician applied longitudinal magnetism to the crankshaft to check for transverse cracks before reassembling the engine.
Example Sentence 2
East and west headings revealed the largest deviation caused by the aircraft's longitudinal magnetism during the swing.