Definition
On a Traffic Collision Avoidance System (TCAS) or traffic display, the vertical position of another aircraft expressed as a difference from your own aircraft's altitude rather than as an absolute altitude. It is shown as a small number near the traffic symbol, typically in hundreds of feet, with a plus sign indicating the other aircraft is above you and a minus sign indicating it is below.
Plain English
How high or low another aircraft is compared to you right now. A plus number means it's above you; a minus number means it's below you. The number tells you the difference in hundreds of feet.
Context Anchor
Seen on cockpit traffic displays and safety-system pages that show nearby aircraft around your own aircraft.
Derivation
Altitude comes from the Latin altus, meaning “high.” In this phrase, “in relation to” means the height is being compared to your aircraft, not measured from the ground or sea level.
Why Pilots Care
Allows immediate visual judgment of terrain clearance and traffic separation without converting absolute altitudes.
Analogy
It is like saying someone is two floors above you in a building. You are not naming the floor they are on; you are comparing their height to yours.
Grounding Statement
If a traffic symbol shows +05, the other aircraft is 500 feet above your aircraft; if it shows -05, it is 500 feet below you.
Intuition Check
Do not assume this is the other aircraft’s actual altitude. Here, it means altitude compared with your aircraft’s altitude.
Example Sentence 1
The traffic display showed a target at minus 03, meaning the other aircraft was 300 feet below us.
Example Sentence 2
Traffic appeared at minus 500 feet altitude in relation to your aircraft on the TCAS screen.