A glider is a light aircraft with no engine, and the glider is a vehicle often seen throughout cult-TV history.
An episode of the second season is called "Reunion," and the narrative revolves around a glider. The episode begins in Germany at the start of World War II (just after the invasion of Poland). A group of friends share a picnic, and fly a glider.
But the glider disappears, with its pilot aboard.
What is found in the cockpit is genuinely disturbing; the stuff of nightmares.
Gliders have also appeared in other series, including Valley of the Dinosaurs (1974; CBS), and other series as well.