Calculating a standard 3-degree descent path is a fundamental skill for pilots to ensure a smooth transition from cruise to landing. A common "Rule of Thumb" is the 3-to-1 rule: for every 1,000 feet of altitude you need to lose, you should plan for 3 nautical miles (NM) of horizontal travel. For example, if you are at 30,000 feet and need to reach sea level, you should start your descent 90 NM away (30×3=90). To determine the required Rate of Descent (ROD) in feet per minute, a quick formula is to multiply your groundspeed by 5. If you are traveling at 400 knots, you would need a descent rate of roughly 2,000 feet per minute (400×5=2000). More precisely, Rate=Groundspeed×tan(3∘)×(101.27/60). In 2026, while Flight Management Systems (FMS) automate these calculations using vertical navigation (VNAV), pilots still monitor these basic formulas to verify that the aircraft is "on profile" and to manage energy effectively during the approach.