Additional note on calculating ROD/ROC
The same principle can be used in all situations—regardless of altitude, including during approach.
Use feet per nautical mile (ft/NM) ÷ 60, then multiply the result by ground speed (GS) to get the required rate.(This method is more accurate and precise than using ground speed multiplied directly by the gradient.)
Example (approach):
A 3° approach is approximately 300 ft/NM
→ 300 ÷ 60 = 5
→ ROD ≈ GS × 5
(More precisely, 3° ≈ 318 ft/NM → GS × 5.3)
At higher altitude:
The same ft/NM concept applies.
Example:
Descend 6000 ft within 20 NM
→ 6000 ÷ 20 = 300 ft/NM
→ 300 ÷ 60 = 5
→ Rate = GS × 5
(500x5 =2500feet/min -high alt)
(300x5=1500feet/min -lower alt)
Another example:
Descend 12000 ft within 20 NM
→ 12000 ÷ 20 = 600 ft/NM
→ 600 ÷ 60 = 10
→ Rate = GS × 10
This method does not depend on altitude or Mach number.
If you understand it but cannot achieve the required rate, you can always use an alternative method or inform ATC.
Each pilot may have different techniques—none are wrong. It depends on what you are most comfortable using.