Definition
Two or more aircraft operating at the same altitude at the same time. The term is used by controllers and pilots to identify traffic that shares a flight level or assigned altitude, which affects separation requirements and traffic awareness.
Plain English
Aircraft flying at the same height as you. If another aircraft is at your altitude, the two of you are co-altitude.
Context Anchor
Seen in arrival, traffic, and instrument procedure discussions when comparing your aircraft’s position with other aircraft nearby.
Derivation
The prefix 'co-' comes from Latin meaning 'together' or 'with.' Combined with altitude, it simply means 'together at the same altitude' — the same way 'co-pilot' means 'pilot together with.'
Why Pilots Care
Controllers and pilots must apply lateral or longitudinal separation rules to prevent mid-air conflicts when aircraft are at the same height.
Intuition Check
Do not read co-altitude as meaning the aircraft are flying together or coordinated. Here it means they are at the same, or almost the same, altitude.
Example Sentence 1
ATC advised, 'Traffic, twelve o'clock, two miles, co-altitude,' so the pilot began an immediate visual scan straight ahead.
Example Sentence 2
The pilot spotted a co-altitude aircraft ahead and requested a slight descent to increase vertical spacing.