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

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.