Performance Class B (CS-23): Use of Aeroplane Performance Data

032-03-03Pablo Asensio Martínez2026-04-011 min

Interpreting Performance Graphs

Manuals provide performance data in tabular or graphical formats. It is essential to enter the graph correctly and follow the lines accurately.

Common Variables

  • Pressure Altitude (PA): Altitude above the standard datum plane (1013.25 hPa).
  • Temperature (OAT): Outside Air Temperature. Often converted to ISA Deviation (e.g., ISA +10°C).
  • Weight: Aircraft mass at the start of the phase.
  • Wind Component: Headwind or Tailwind.

Example: Take-Off Distance Graph

  1. Enter with OAT: Find the temperature on the first axis.
  2. Move to Pressure Altitude: Follow the line to the PA reference line and parallel the graph lines to the specific PA.
  3. Move to Weight: Move horizontally to the reference line, then parallel the relevant weight lines.
  4. Move to Wind: Move horizontally to the reference line, then parallel the wind component lines.
  5. Read Result: Move horizontally to read the Take-Off Distance Required (TODR).

Corrections

Always apply corrections in the order specified by the graph (usually Temp $\rightarrow$ Alt $\rightarrow$ Weight $\rightarrow$ Wind $\rightarrow$ Slope $\rightarrow$ Surface).

Slope Correction

  • Upslope: Increases Take-off Distance (aircraft works against gravity). Decreases Landing Distance (gravity aids braking).
  • Downslope: Decreases Take-off Distance (gravity aids acceleration). Increases Landing Distance.

Surface Correction

  • Grass/Gravel: Increases rolling friction, increasing Take-off Distance.
  • Wet: Reduces braking effectiveness, increasing Landing Distance.

Interpolation and Extrapolation

  • Interpolation: Estimating a value between two known values (e.g., weight 2500 kg between 2000 and 3000 kg). Allowed and necessary.
  • Extrapolation: Estimating a value outside the range of the graph. Dangerous and usually prohibited as performance relationships may not be linear.