ESDU 88030 estimates the onset of non-linear aerodynamic characteristics by giving an empirical method for predicting the incidence and corresponding lift coefficient for either initial leading- or trailing-edge separation. The method developed treats the incidence as contributed to by three components: one from a datum plane wing, and one each from the superimposed effects of camber and twist. It is applicable strictly to aerodynamically smooth wings provided that the local effective twist does not exceed 10 degrees and will not apply when the leading-edge is rough, as with ice accretion. Wide, practical, ranges of planform and flow conditions are covered by the method (including aspect ratios from 1.4 to 12 and leading-edge sweeps from zero to 62 degrees). The method applies to any camber line slope, which may vary spanwise, as may the thickness/chord ratio, and comparisons are shown between predicted lift coefficient for the onset of separation for both leading- and trailing-edge types which show it is predicted to within 15 per cent. Comprehensive practical worked examples illustrate the use of the method, and a calculation summary sheet guides the user step-by-step through the procedure.