Heading: true → compass
Compass heading steered differs from true track by three corrections:
compass heading = true track + WCA + variation + deviation
| Step | Term | Meaning |
|---|---|---|
| Start | True track | Route line direction on chart. Measure: chart-track |
| +WCA | Wind (WCA) | Wind pushes sideways, so angle into it (wind from right, crab right). Definition: nav-definitions |
| = | True heading | Direction nose must point to hold track, clockwise from true north (PHAK ch.16) |
| +Var | Variation | Angle between true and magnetic north. Result: magnetic heading |
| +Dev | Deviation | Small leftover compass error. Result: compass heading |
Definitions, isogonic & agonic lines, deviation card: variation-deviation-conversion.
Signs: true to compass, variation and deviation signed West +, East −, so chain is one addition. Mnemonic: "east least, west best".
Trap: variation applied the wrong way doubles the error instead of cancelling it; reporting the magnetic heading when the compass heading was asked (or the reverse); forgetting deviation leaves a couple degrees off.
References
- AC 100-001 glossary
- PHAK ch.16
- PHAK ch.8 (FAA-H-8083-25)