Vertical glide slope control system including complementary filter

A vertical glide slope control system including a complementary filter. Complementary aircraft generated and processed signals are added to a glide slope error signal which may include distortions. The results of the summation are applied to a first order lag filter having a low breakpoint (i.e., a low-pass band). The low-pass band eliminates high frequency distortions contained in the glide slope error signal without loss of stability. Aircraft stability is not lost due to the inclusion of the complementary aircraft signals added prior to the passage of the signals through the first order lag filter.