Use and Interpretation of the Aeroplane Flight Manual and Performance Charts
The AFM/POH as the legal source
The Aeroplane Flight Manual is the approved document; the POH may be a manufacturer's document with equivalent data. Performance data in the AFM is scheduled (conservative) and must be used as published. Charts are typically presented for a reference mass, ISA, sea level, zero wind, dry runway and zero slope, with correction factors applied afterwards.
Reading a chart
Identify the axes, the units, the reference conditions and the direction of the correction. A typical take-off chart has pressure altitude on one axis, temperature on the other, with a family of curves for mass and a separate wind/slope correction graph. Interpolation between curves is normal; extrapolation beyond the published envelope is not permitted. Note whether the chart gives TODR or TOR and whether the result already includes the 1.15 factor.
Corrections and traps
Apply corrections sequentially and in the order the chart specifies; a common error is to apply wind and slope corrections to the unfactored distance and then multiply, or to apply a percentage correction to the wrong base. Watch for chart units (feet vs metres, lb vs kg, °C vs °F), density altitude vs pressure altitude entry, and charts that already include a 5 kt or 50 ft allowance. Always check the limitations section for the maximum tailwind, crosswind and contaminated-runway data.
Worked example
Chart gives TODR 1,650 m at 60 t, sea level, ISA. Correction graph: −8% for 10 kt headwind, +4% for 0.8% uphill. Apply multiplicatively: 1,650 × 0.92 × 1.04 ≈ 1,579 m. Compare with TODA 1,600 m - acceptable, but only just.
Traps
Extrapolating outside the envelope; using the wrong altitude entry; forgetting the chart's built-in factor; mixing units.