The external systematic accuracy of the HIPPARCOS positions and proper motions in the equatorial zone as represented by the subset of its bright FK5 stars is estimated by comparison with modern ground-based catalogues of 1980-1990s as well as with the most precise compiled catalogues made in the 20th century. Significant zonal and regional systematic differences between Hipparcos and ground-based catalogues have been detected for the different epochs ranging from 1920 to 1990. The most typical behaviour of the analysed differences at the epoch 1991.25 is almost absence of small-scale deviations and presence of the large-scale features. For the epoch 1920, both large and small-scale discrepancies are more pronounced reaching up to 50 mas. This gives evidence of the inferiour consistency of the HIPPARCOS system with ground-based observations comparing with the best compiled catalogues.