Plain English Meaning
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.
Full 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.
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.