  The KDA (Kaiser, Dennett-Thorpe & Alexander, 1997) EXT model, that is, the
extension of the KDA model of FR (Faranoff & Riley) II-type source evolution,
is applied and confronted with the observational data for selected FR II-type
radio sources with significantly aged radio spectra. A sample of FR II-type
radio galaxies with radio spectra strongly bent at their highest frequencies is
used for testing the usefulness of the KDA EXT model.The dynamical evolution of
FR II-type sources predicted with the KDA EXT model is briefly presented and
discussed. The results are then compared to the ones obtained with the
classical KDA approach, assuming the source's continuous injection and
self-similarity. The results and corresponding diagrams obtained for the eight
sample sources indicate that the KDA EXT model predicts the observed radio
spectra significantly better than the best spectral fit provided by the
original KDA model.
