3-Degree Descent Rate

A standard 3° descent path has a nearly fixed slope, so the vertical speed needed depends on how fast the aircraft is moving across the ground. The rule of thumb ROD ≈ GS × 5 comes from converting that shallow angle into feet per minute, and it works well for typical approach speeds in knots. It is only an approximation, but it is fast and close enough for most visual or instrument approach planning.

Use this when planning a normal instrument or visual approach to estimate the descent rate needed to stay on a 3° glide path. It is especially useful when ATC gives you a speed and you need a quick mental check of your vertical speed target.

• Using indicated airspeed instead of ground speed, which can give the wrong descent rate in wind
• Forgetting that the rule is approximate and may need slight adjustment for local conditions or aircraft performance
• Mixing up descent rate with altitude lost over distance, which are related but not the same quantity