Required Climb Rate from Gradient (the AIM Table, Live)

TERPS obstacle evaluation: when terrain or towers penetrate the standard 40:1 departure surface (152 ft/nm, protected by requiring 200), the procedure publishes the steeper gradient that clears them — '410 ft/nm to 8,400' — sometimes with a low-close-in obstacle note besides. The number is the mountain's geometry translated into your contract.

Vx maximizes gradient through the air — necessary but not sufficient. The requirement is over the ground: a tailwind on departure dilutes even a Vx climb's ft/nm (and density altitude erodes the rate itself). Compute the required fpm at your actual GS, compare with honest aircraft performance at today's weight and DA — that comparison is the go/no-go, not the speed choice alone.

Then that departure isn't available to you as published: wait for better climb conditions (cooler, lighter), use a different runway/procedure, or — where offered — the 'diverse vector area' or a visual-climb-over-airport (VCOA) option designed for exactly this. Taking off anyway and 'climbing in the hold' improvises terrain separation that the procedure was built to guarantee.

Legally no — VFR terrain avoidance is see-and-avoid. Practically, the same physics kills: a high-DA VFR departure toward rising terrain wants exactly this computation with the terrain's own gradient (our obstacle-departure tool computes it). Instrument paperwork aside, ft/nm-versus-terrain is universal aviation arithmetic.