Complex sentence: If carrying out an emergency landing, the gliding range sets the absolute maximum on the distance away that a possible emergency landing site may be, though in practice it is much easier and safer to choose a much closer site.
Split into simpler sentences: If carrying out an emergency landing, the gliding range sets the absolute maximum on the distance away that a possible emergency landing site may be. In practice, however, it is much easier and safer to choose a much closer site.