Koch Chart
Density-altitude–corrected takeoff distance with a safety margin and runway-length check.
1. Airport & weather
Runway in use
2. Aircraft & margin
3. FAA Koch chart
Tick positions measured from the original FAA chart. The red line is drawn from your current temperature to your current pressure altitude; the marker shows where it crosses the middle scale. The calculator reads its takeoff and climb numbers directly from this crossing — chart and calculator agree by construction.
4. Result
- Pressure altitude
- Density altitude
- Takeoff distance increase
- Climb-rate decrease
- Corrected ground roll
- With safety margin
- Runway available
- Selected runway
- Wind component
- Runway slope
Factors this calculator does not model
The Koch chart bundles density-altitude effects on engine power, propeller efficiency, and aerodynamic lift into a single nomogram. Everything below shifts real takeoff and climb performance and is on you to account for separately — usually by adding margin.
Outside the chart's scope
- Aircraft type: chart was built for normally-aspirated piston singles. Turbocharged, turboprop, and turbine aircraft follow different curves; do not use this tool for them.
- Weight: takeoff distance scales roughly with the square of weight. POH ground-roll numbers assume max gross. Lighter aircraft do better; heavier-than-listed is not on the chart.
- Wind component: a 10 kt headwind can cut ground roll by ~20 %; a 10 kt tailwind can add ~20 %. Always use the runway aligned with the wind, and account for gusts.
- Runway slope: uphill takeoffs and downhill landings add significantly to required distance — roughly 10 % per 1 % of slope.
- Surface: dry pavement is the baseline. Grass adds 15–20 %, wet grass 25–40 %, soft/snow/standing water far more.
- Runway condition: rough, contaminated, or poorly maintained surfaces increase rolling friction beyond the POH baseline.
- Obstacles: chart gives ground roll only — total distance over a 50 ft obstacle is typically 1.5–2× ground roll, and climb gradient over rising terrain is what actually kills mountain takeoffs.
- Humidity: high humidity reduces engine power 1–3 % beyond the dry-air density-altitude calculation.
- Mixture leaning: a full-rich mixture at high DA loses significant power; the chart assumes the engine is correctly leaned for the conditions.
- Pilot technique: rotation speed, flap setting, brake release timing, and soft-field/short-field technique each move actual distance by 5–15 %.
- Aircraft condition: engine wear, propeller pitch, tire pressure, brake drag, and airframe cleanliness all degrade performance vs. a new-aircraft POH.
Limits of the digitization
- Tick positions were pixel-measured from a scan of the FAA chart. Readings are reliable to roughly ±5 percentage points on the takeoff scale near the top, where ticks are tightly packed.
- Off-scale conditions (very high DA) are linearly extrapolated past the chart's last tick — treat as worst-case ballpark, not a real reading.
- aviationweather.gov values are airport-reporting-station METARs; conditions on your specific runway can differ, especially with terrain effects.
Weather data from aviationweather.gov. Always cross-check against your aircraft's POH performance tables before flight.