Definition
Two angles whose measures add up to exactly 90 degrees.
Plain English
Two angles that, when placed together, form a right angle. If one angle is 30 degrees, its complementary angle is 60 degrees.
Context Anchor
Seen in aviation math, basic geometry, navigation problems, and aircraft or maintenance drawings that use right triangles or right-angle references.
Derivation
From the Latin complementum, meaning 'that which fills up' or 'completes.' The two angles 'complete' a right angle (90 degrees) together. Knowing this helps the term feel less abstract: each angle is the missing piece that finishes the 90-degree corner.
Why Pilots Care
Pilots may meet this term when reading training material that explains angles, triangles, or diagram-based calculations. Knowing it prevents confusion between angles that add to 90 degrees and angles that add to other totals.
Analogy
Think of the corner of a sheet of paper. If one angle takes part of that corner and another angle takes the rest, the two angles are complementary.
Intuition Check
Complementary does not mean free, extra, or merely matching. Here it means the two angles complete a 90-degree angle together.
Example Sentence 1
If the rib of a wing meets the spar at 25 degrees, the complementary angle on the other side of the right angle is 65 degrees.
Example Sentence 2
Complementary angles appeared in the wind-correction diagram, allowing the student to find the required drift angle quickly.