1. What is Top of Descent?

The Top of Descent (TOD) is the point in flight where a pilot should begin descending to reach the destination airport at the desired altitude. Calculating this correctly ensures a smooth, efficient descent profile.

2. How Does the Calculator Work?

The calculator uses the standard TOD formula:

Where:

• \( CA \) — Cruise Altitude (feet)
• \( DA \) — Destination Altitude (feet)
• \( DR \) — Descent Rate (feet per minute)
• \( GS \) — Ground Speed (knots)

Explanation: The formula calculates the distance needed to descend from cruise altitude to destination altitude at the given descent rate, adjusted for ground speed.

3. Importance of TOD Calculation

Details: Accurate TOD calculation is crucial for flight planning, fuel efficiency, passenger comfort, and ATC compliance. Starting descent too early wastes time and fuel, while starting too late may require steep descents.

4. Using the Calculator

Tips: Enter cruise altitude and destination altitude in feet, descent rate in feet per minute, and ground speed in knots. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical descent rate for commercial aircraft?
A: Most commercial jets descend at 500-2000 fpm, with 1000-1500 fpm being typical for passenger comfort.

Q2: How does wind affect TOD calculation?
A: Ground speed already accounts for wind. Headwinds decrease GS (earlier TOD), tailwinds increase GS (later TOD).

Q3: Should I add any buffer to the calculated TOD?
A: Many pilots add 5-10% as a safety buffer, especially in busy airspace or when ATC may delay descent.

Q4: How does temperature affect descent planning?
A: In very cold conditions, true altitude is lower than indicated, potentially requiring earlier descent.

Q5: What about step-down descents?
A: For step-down descents, calculate each segment separately and sum the distances.