Definition
The order in which two or more aircraft are cleared to approach to land at an aerodrome, as established by air traffic control.
Plain English
The line-up order ATC sets for arriving aircraft so each one knows when it is its turn to land.
Context Anchor
Used in air traffic control communications when several aircraft are arriving at the same airport or landing area.
Derivation
From Latin sequentia, meaning 'a following.' A sequence is simply the order in which things follow one another. In this context it is the following order of aircraft on approach.
Why Pilots Care
Your place in the sequence determines when you can land, how much fuel you need to carry, and how you manage speed and configuration on arrival.
Intuition Check
Do not read approach sequence as the flight path or approach procedure itself. Here it means the assigned order of arriving aircraft.
Example Sentence 1
Tower advised us we were number three in the approach sequence behind a regional jet and a light twin.
Example Sentence 2
Heavy traffic forced the controller to extend the approach sequence, adding ten miles to our final.