Definition
Successively lower minimum altitudes published along an instrument approach segment that allow an aircraft to descend in stages as it passes specified fixes inbound to the runway. Each step-down altitude is the lowest altitude the aircraft may be flown until the next fix is crossed, at which point a further descent to the next lower published altitude is permitted.
Plain English
On many instrument approaches, you don't descend in one smooth slope. Instead, the chart gives you a series of lower altitudes, and you can drop to each new one only after passing a specific point on the approach. These staged altitudes are the step-down altitudes.
Context Anchor
Seen on instrument approach charts, especially during nonprecision approaches and when joining the final approach course after radar vectors.
Derivation
“Step-down” describes descending in steps instead of one continuous drop. That picture helps: each published altitude is like a lower step that becomes available only after you reach the proper charted point.
Why Pilots Care
They guarantee obstacle clearance while allowing a safe, gradual descent; violating them risks terrain conflict or procedure non-compliance.
Analogy
Think of walking down stairs in the dark with a handrail: you move to the next lower step only when you have reached it. Step-down altitudes work the same way on the chart—you descend only when the procedure says the next lower level is available.
Intuition Check
Do not assume a clearance for the approach lets you descend straight to the runway. Step-down altitudes are minimum altitudes you must respect until the correct charted point is passed.
Example Sentence 1
After crossing the final approach fix, the pilot descended to the next step-down altitude shown on the approach chart.
Example Sentence 2
The controller cleared us to 3000 feet and we began tracking the step-down altitudes shown on the approach plate.