Aviation Climb Gradient Calculator
1. Calculate Gradient from ROC
Determine your climb gradient based on ground speed and rate of climb.
2. Calculate Required ROC
Determine the vertical speed needed to meet a specific gradient requirement.
Understanding Climb Gradient in Aviation
In aviation, the climb gradient is a critical performance metric that relates the altitude gained to the horizontal distance covered over the ground. Unlike the "Rate of Climb" (ROC), which is time-dependent (feet per minute), the climb gradient is distance-dependent (feet per nautical mile or percentage).
Why Climb Gradient Matters
Pilots must calculate climb gradients primarily for obstacle clearance and to comply with Standard Instrument Departures (SIDs). Air traffic control and departure procedures often mandate a minimum gradient to ensure an aircraft stays safely above terrain or buildings following takeoff.
The Formulas
To calculate the climb gradient in feet per nautical mile (ft/NM):
Gradient (ft/NM) = (Rate of Climb × 60) ÷ Ground Speed
To calculate the required Rate of Climb (ROC) for a specific gradient:
ROC (fpm) = (Gradient × Ground Speed) ÷ 60
Gradient Percentage
The percentage of climb is calculated by taking the rise over the run. Since 1 Nautical Mile is approximately 6,076.1 feet:
Gradient % = (ft per NM ÷ 6076.1) × 100
Real-World Example
Imagine you are departing an airport where the SID requires a climb gradient of 300 ft/NM until reaching 5,000 feet. If your aircraft's ground speed during the climb is 120 knots, what is your required Rate of Climb?
- Ground Speed: 120 kts
- Required Gradient: 300 ft/NM
- Calculation: (300 × 120) / 60 = 600 fpm
In this scenario, you must maintain a vertical speed of at least 600 feet per minute to stay clear of obstacles and remain compliant with the procedure.