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function calculateRateOfClimb() {
// Get input values
var gsInput = document.getElementById('groundSpeed');
var gradientInput = document.getElementById('climbGradient');
var resultBox = document.getElementById('resultBox');
var rocResult = document.getElementById('rocResult');
var gradientPercentDisplay = document.getElementById('gradientPercent');
var gs = parseFloat(gsInput.value);
var gradient = parseFloat(gradientInput.value);
// Validation
if (isNaN(gs) || isNaN(gradient) || gs <= 0 || gradient <= 0) {
alert("Please enter valid positive numbers for Ground Speed and Climb Gradient.");
resultBox.style.display = "none";
return;
}
// Calculation: ROC (fpm) = (Ground Speed * Gradient) / 60
// We divide by 60 to convert Knots (NM per hour) to NM per minute.
var roc = (gs * gradient) / 60;
// Calculate gradient as a percentage for extra info
// 1 NM = 6076.12 feet.
// Percent = (Rise / Run) * 100 = (Gradient / 6076.12) * 100
var percent = (gradient / 6076.12) * 100;
// Display results
resultBox.style.display = "block";
rocResult.innerHTML = Math.round(roc) + " fpm";
gradientPercentDisplay.innerHTML = "Equivalent Gradient: " + percent.toFixed(2) + "%";
}
How to Calculate Rate of Climb (ROC)
Calculating the Rate of Climb (ROC) is a critical skill for pilots, particularly during Instrument Flight Rules (IFR) departures or when clearing obstacles near an airport. The Rate of Climb represents the vertical speed of an aircraft, typically measured in feet per minute (fpm).
While your Vertical Speed Indicator (VSI) shows your current performance, flight planning requires you to calculate the required rate of climb to ensure you can meet the climb gradients specified in Standard Instrument Departures (SIDs) or Obstacle Departure Procedures (ODPs).
The Rate of Climb Formula
The standard aviation formula to convert a required climb gradient (in feet per nautical mile) to a vertical speed (in feet per minute) is dependent on your ground speed.
ROC (fpm) = [Ground Speed (kts) × Climb Gradient (ft/nm)] ÷ 60
Variables defined:
- Ground Speed (GS): The speed of the aircraft relative to the ground. This differs from Indicated Airspeed (IAS) due to wind and altitude. A tailwind increases ground speed, requiring a higher rate of climb to maintain the same angle.
- Climb Gradient: The ratio of altitude gained to distance traveled, usually expressed in feet per nautical mile (ft/nm). The standard IFR minimum climb gradient is 200 ft/nm.
Why Ground Speed Matters
Many pilots mistakenly use their Indicated Airspeed (IAS) for this calculation. However, the geometry of climbing over a fixed point on the earth depends on how fast you are moving across the ground.
For example, if you need to climb 300 feet for every mile you travel forward:
- At 90 knots ground speed: (90 × 300) / 60 = 450 fpm.
- At 120 knots ground speed: (120 × 300) / 60 = 600 fpm.
As you can see, the faster your ground speed, the higher your vertical speed must be to maintain the same climb angle (gradient).
Converting Gradient Percentages
Sometimes, departure procedures express the climb requirement as a percentage (e.g., "Climb 5%"). To use the standard formula, you first convert the percentage to feet per nautical mile.
Since 1 Nautical Mile is approximately 6,076 feet:
ft/nm = Gradient % × 60.76
For a rough mental estimate, you can simply multiply the percentage by 60. For example, a 5% gradient is roughly 300 ft/nm (5 × 60 = 300).
Practical Application for Pilots
When reviewing a departure plate, look for the "Takeoff Minimums" section. If a specific climb gradient is required (e.g., "350 ft/nm to 5000"), use the calculator above with your expected ground speed.
Always add a safety margin. If the calculation shows you need 600 fpm, and your aircraft's Pilot's Operating Handbook (POH) states a maximum climb rate of 650 fpm at that density altitude, you have a very narrow margin for error, especially if you encounter downdrafts or turbulence.