Descent Planning: Optimize Your Flight Profile

The Top of Descent (TOD)

Knowing exactly when to start your descent from cruise altitude is a hallmark of professional flying. Starting too early means spending more time at lower altitudes burning more fuel. Starting too late requires a rapid, steep descent that can shock-cool the engine and cause passenger ear discomfort.

The 3-to-1 Rule

A classic aviation rule of thumb for a standard 3-degree descent profile is the 3-to-1 rule: multiply the altitude you need to lose (in thousands of feet) by 3. For example, if you are cruising at 10,000 feet and need to reach a pattern altitude of 1,000 feet, you need to lose 9,000 feet.

9 x 3 = 27. Therefore, you should begin your descent 27 Nautical Miles out from the airport.

Calculating Rate of Descent

Once you know when to start down, you need to know how fast to descend. To maintain a 3-degree path, multiply your Ground Speed in knots by 5. If your ground speed in the descent will be 120 knots, 120 x 5 = 600. You need a descent rate of 600 feet per minute (FPM).

Managing Energy

Descent planning is energy management. You are trading altitude (potential energy) for airspeed (kinetic energy). If you need to descend rapidly but cannot let your airspeed build up into the yellow arc, you must reduce power, add drag (flaps/gear if within speed limits), or perform a forward slip.

Using a descent calculator removes the mental math, allowing you to input your exact ground speed and altitude targets to find the perfect Top of Descent point and FPM rate.