The KASCADE experiment measures extensive air showers. It is 100% efficient for showers which are induced by primary particles with energies above 10 15 eV to pursue its main goal, the examination of the knee in the flux spectrum at ≈ 5 · 10 15 eV. A specially adapted method to calculate two observables (Nch, the number of charged particles and Nµ, the number of muons) by means of a maximum likelihood estimate will be presented. The estimate combines different detector systems and works already at energies around the trigger threshold of KASCADE at ≈ 10 14 eV. These observables are used to reconstruct a preliminary energy flux spectrum which is compared with direct measurements and previous measurements of KASCADE at energies above 10 15 eV. The reconstruction of energy spectrum and elemental composition around the trigger threshold of KASCADE is important for two reasons. First the estimated spectrum at higher energies has to be congruent with the results of direct measurements. Second it is a cross-check of the interaction models underlying the analysis of extended air