I mentioned AIM 5-4-20.d. before, now I'll revisit it.
d. Side-Step Maneuver Minimums. Landing
minimums for a side-step maneuver to the adjacent
runway will normally be higher than the minimums
to the primary runway.
Why would the Side-Step Maneuver Minimums "normally be higher than the minimums to the primary runway"? Look at how the minimums are derived.
5-4-20. is titled
Approach and Landing Minimums, and it discusses a. Landing Minimums, b. Obstacle Clearance, and more. Under the second sub-paragraph, we get a glimpse into
why the minimums might be higher:
b. Obstacle Clearance. Final approach obstacle
clearance is provided from the start of the final
segment to the runway or missed approach point,
whichever occurs last. Side-step obstacle protection
is provided by increasing the width of the final
approach obstacle clearance area.
The non-precision minimums for the straight-in approach do
not take into account obstacles that may affect the adjacent runway. Circling minimums for the approach would account for those obstacles, and side-step minimums would account for them, but straight-in non-precision minimums would not account for them.
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