Glideslope Descent Rate Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Staying on the glidepath during an approach
Maintaining a precise glideslope angle during an ILS or visual approach requires a specific vertical descent rate that changes directly with groundspeed - flying the same descent rate at different approach speeds would drift the aircraft off the correct glidepath.
Worked example
For 120 knots groundspeed on a standard 3-degree glideslope:
Descent Rate = 120 x 101.27 x tan(3°) = 636.9 feet per minute
A widely used pilot rule of thumb approximates this as simply groundspeed x 5 for a standard 3-degree glidepath - in this example, 120 x 5 = 600 fpm, reasonably close to the more precise calculated value of 636.9 fpm, making it a handy quick mental estimate during an approach briefing.