Definition
An ATC altitude restriction requiring an aircraft to be at or lower than a specified altitude when crossing a designated fix. The pilot may cross the fix at the stated altitude or any altitude beneath it, but not above.
Plain English
When you reach this point on the route, you must be at this altitude or lower — never higher.
Context Anchor
Seen in instrument clearances, arrival procedures, departure procedures, and altitude restrictions on charts.
Derivation
Cross means to pass over or through a point. Fix in navigation means a known position, not something being repaired. Together, the phrase means passing a known navigation point while meeting the altitude limit attached to it.
Why Pilots Care
Compliance maintains required obstacle clearance and traffic separation.
Intuition Check
Do not read “fix” as something to repair; here it means a named position in the sky or on a chart. “At or below” does not mean “descend as low as you want”; it means “not higher than this altitude,” while still obeying any other minimum or assigned altitude.
Example Sentence 1
The STAR required us to cross BRAVO intersection at or below 10,000 feet, so we began our descent twenty miles out.
Example Sentence 2
The published procedure requires crossing the VOR at or below 6000 feet.