Complex sentence: The glider and the pilot (s) can be retrieved by road from the outlanding location using a purpose-built trailer or sometimes a tow-plane can be summoned to re-launch the aircraft.
Split into simpler sentences: The glider and the pilot (s) can then be retrieved by road from the outlanding location using a purpose-built trailer. In some instances, a tow-plane can be summoned to re-launch the aircraft.