Glidepath Rate of Descent

ROD = ground speed x 101.27 x tan(angle) ft/min, and the path itself is 6076.12 x tan(angle) ft/nm -- 318 ft/nm at a standard 3.00 degree ILS, the exact FAA TERPS figure that fixes the tangent form. At 120 kt on a 3-degree path that is 637 ft/min, which the 'ground speed x 5' rule rounds to 600. Because it scales with GROUND speed, a tailwind or a faster approach demands a higher descent rate to stay on the same path. A planning aid, not a clearance; the approach chart and the pilot in command govern.

rod_fpm = ground_speed_kt x 101.269 x tan(glidepath_angle); ft_per_nm = 6076.12 x tan(glidepath_angle). The 101.269 converts knots (nm/hr) to ft/min (x 6076.12 / 60).

Required rate of descent on a glidepath (FAA Instrument Flying Handbook; TERPS Order 8260.3), by name; the approach chart and the pilot in command govern.

The descent-triangle trigonometry is first-principles; the glidepath angle and ground speed come from the approach and the flight instruments.

Estimate. AHJ and licensed professional govern.

Field names used by the API: ground_speed_kt, glidepath_angle_deg, rod_fpm, ft_per_nm

• Tangent form the vertical rate uses tan(angle), fixed by TERPS's 318 ft/nm at 3.00 degrees (not sine)FAA TERPS 8260.3
• Ground speed drives it ROD scales with ground speed, so wind and true airspeed change the required rateFAA IFH