If final approach GS is 100 knots, what descent rate is needed to maintain a 3-degree glideslope?

If final approach GS is 100 knots, what descent rate is needed to maintain a 3-degree glideslope?

• A. 400 FPM
• B. 500 FPM
• C. 600 FPM
• D. 700 FPM

Answer: (B)

On a 3-degree glide slope, the vertical speed you need is the horizontal speed multiplied by the slope’s tangent. Convert the horizontal speed to feet per minute and apply tan(3°). Tan(3°) is about 0.0524. With a ground speed of 100 knots, the horizontal rate is 100 knots × 101.27 ft/min per knot ≈ 10,127 ft/min. Multiply by 0.0524 to get a descent rate of roughly 530 ft/min. Since the choices are approximate, 500 ft/min is the closest and best match for a 3-degree descent at 100 knots.

On a 3-degree glide slope, the vertical speed you need is the horizontal speed multiplied by the slope’s tangent. Convert the horizontal speed to feet per minute and apply tan(3°).

Tan(3°) is about 0.0524. With a ground speed of 100 knots, the horizontal rate is 100 knots × 101.27 ft/min per knot ≈ 10,127 ft/min. Multiply by 0.0524 to get a descent rate of roughly 530 ft/min.

Since the choices are approximate, 500 ft/min is the closest and best match for a 3-degree descent at 100 knots.