Definition
A waypoint on a published instrument procedure that has a mandatory altitude restriction the aircraft must satisfy — at, at or above, at or below, or within a specified altitude window — when crossing that point.
Plain English
A point on the route where the chart tells you exactly what altitude (or range of altitudes) you must be at when you fly over it.
Context Anchor
Seen on published arrival and approach charts and in the aircraft’s navigation computer when planning a climb or descent.
Derivation
‘Constrained’ comes from the Latin constringere, meaning ‘to bind or tie tightly.’ The waypoint is ‘tied’ to a specific altitude requirement — the aircraft is not free to cross it at any altitude.
Why Pilots Care
Allows the FMS to build a vertical path that meets all restrictions while maintaining terrain and traffic separation.
Analogy
Think of it like a checkpoint on a road trip where you not only have to pass the checkpoint, but also have to arrive there at a required time. The point matters, and the condition attached to it matters too.
Intuition Check
Constrained does not mean the waypoint is blocked or difficult to reach. It means a required condition, usually an altitude, is tied to crossing that point.
Example Sentence 1
The crew programmed the descent so the aircraft would meet the constrained waypoint at or above 11,000 feet.
Example Sentence 2
Before activating VNAV the pilot verified every constrained waypoint on the arrival to confirm the profile would work.