Definition
Altitude constraints published on instrument procedures or issued by ATC that require an aircraft to cross a specified fix at, at or above, at or below, or between specified altitudes during descent. They are used to ensure terrain and obstacle clearance, traffic separation, and an orderly flow into the terminal area.
Plain English
Rules that tell a pilot what altitude to be at when crossing a particular point as the aircraft is coming down. The rules can say 'be at this altitude,' 'be at or above,' 'be at or below,' or 'stay between two altitudes.'
Context Anchor
Seen on instrument approach charts, arrival procedures, and in air traffic control clearances that include altitude limits.
Derivation
Descent comes from a Latin word meaning “to climb down.” Restriction comes from a Latin word meaning “to bind back” or “hold within limits.” Together, the phrase means that the aircraft’s downward movement is held within specific limits.
Why Pilots Care
Missing a descent restriction can put the aircraft too close to terrain, into conflicting traffic, or out of compliance with the clearance. On many arrivals the restrictions are mandatory unless ATC specifically cancels them with phrasing like 'descend via' versus 'descend and maintain.'
Grounding Statement
A descent restriction is like a floor in the sky: the aircraft may not go below it until the procedure or clearance allows it.
Intuition Check
Do not read descent restrictions as a suggestion for a comfortable descent. In instrument flying, they are required altitude limits that control where and how low the aircraft may descend.
Example Sentence 1
Cleared to descend via the arrival, the crew complied with each descent restriction, crossing WAVEY at or above 11,000 feet and ELIOT at 8,000.
Example Sentence 2
ATC added descent restrictions to keep us clear of departing traffic below.